Protecting Plants from Summer Heat

Scorching days have arrived! All but the hardiest of us wilt when outdoor temperatures hit the 90s and 100s, and we seek refuge in air-conditioned places or in water-cooled outdoor areas. Plants don’t have that luxury; they’re literally rooted where they are, and they sometimes need our help to deal with the Central Valley sunlight and heat.

Summer weather can damage plants by stripping them of the moisture they need or by exposing them to more heat or light than they’re adapted to handle. Higher than usual air temperatures, intense light, and overheated or too-dry soil can harm a plant’s leaves, stems, and roots. Wind can further worsen the effects of hot air.

Like humans, plants rely on water partly to cool themselves: we sweat, plants “transpire.” Transpiration is the process by which plants absorb water through their roots, move this water upward through the part of their vascular system called xylem, then lose this water through tiny pores called stomata on the leaf surfaces. The transpiration rate rises in hot temperatures; a plant’s water loss generally doubles with every 18-degree increase.

Plant species vary in the amount of water they need to resist heat and maintain good health (hence their classification as low, medium, or high water use). New plant growth, tender seedlings, fruits and vegetables, and cool-season annuals are particularly susceptible to sun-related damage.

Plants exhibit different levels of heat damage, and it’s important to know the distinction. Wilting is the drooping or shriveling of plant tissues that occurs when they lack sufficient water; it’s reversible if plants are watered in time. (Large-leaved plants will usually wilt a little during peak daytime heat even with adequate water, but will recover when temperatures cool.) Heat stress is when plants begin to suffer irreversible heat-related damage; at this stage, some plants will try to conserve water by dropping leaves or buds. Sunburn (or “leaf scorch”) is when a plant’s leaves or non-woody parts are permanently and severely harmed by excessive heat or sunlight; leaves develop dried brown patches or margins and they eventually wither and fall off. Sunscald is the cracking, discoloration, and warping of bark that occurs when the trunk or branches of a woody plant get too much sun exposure; the damage is permanent and very harmful since it increases the plant’s disease susceptibility.

Follow these simple guidelines to minimize heat damage:

  • Conserve soil moisture and protect plant roots from excessive heat by covering bare ground with a 2- to 4-inch-thick layer of organic mulch—wood chips, shredded bark, leaves.
  • Don’t place inorganic mulches—sand, pebbles, rocks, shredded rubber—or black-tinted mulch near plants in sunny locations (with the exception of desert-adapted plants), because these materials collect and radiate heat.
  • Follow the principle of “right plant, right place.” Select plants adapted to our Mediterranean climate and choose planting locations with proper exposure. (No shade-loving plants in full sun!)
  • Don’t heavily prune trees and shrubs in summer, because this can suddenly expose tender bark to the sun’s intense rays. It also encourages a flush of heat-sensitive new growth and places additional energy and water demands upon heat-stressed plants.
  • Avoid planting during peak summer heat; this stresses plants and compromises their chances of successful establishment. Delay planting until fall, or (if you must plant this season) wait until a cooler spell, plant in the evening, and water deeply after planting.
  • Keep potted plants well watered and (if possible) move them to shadier locations. Use light-colored or plastic containers, which absorb and transmit less heat than dark-colored containers or those made of ceramic, cement, or metal. Hydrogels (water-retaining polymer granules) can be mixed into potting soil to help hold moisture.
  • Whitewash trunks of young trees to help prevent sunscald. Mix equal parts water and white interior latex paint, then apply it from 1 inch below ground to at least 2 feet above ground.
  • Use strategically placed shade cloth to shelter plants.
  • Ensure that plants receive appropriate and consistent levels of water, and check irrigation systems for proper operation. Do this yourself, or enlist the services of a Qualified Water Efficient Landscaper (

Just in case you’re wondering, it’s a myth that water droplets act as miniature magnifying glasses and burn leaves. Overhead watering generally should be avoided for water conservation and disease prevention purposes. . . but sometimes wilting plants (like us!) appreciate a cool sprinkling on a hot summer day.

For gardening related questions, call the UC Master Gardener office at 209-953-6112, or use our website:

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Nectar Guides: How Bees Find Food

Bees see the world differently than humans. The top image shows Black-Eyed Susans as we see them, the bottom as bees see them

Humans love flowers because of their beautiful colors, intriguing shapes, or lovely fragrance. From the plant’s perspective, however, these qualities are more about function than aesthetics. Plants dependent upon pollinators such as bees must make themselves attractive; insects dependent upon plants for nectar or pollen must be attracted to their source.

This last point seems obvious. How could a bee not see a flower? They can, of course, see flowers, though not in the same way humans do. Bees have a total of five eyes: three ocelli, simple eyes located on top of the head, and two large compound eyes, located at either side of the head. The compound eyes have thousands of lenses each, and create a world of movement and light, rather than distinct shapes and outlines.

One amazing thing these eyes do is allow bees to see ultra-violet light, which is invisible to humans. This is important for pollinators because many flowers have “nectar guides”, meaning patterns or markings on the flower that guide bees to a reward of nectar, pollen, or both. Some flowers have nectar guides that are visible to humans, such as Foxglove or Alstroemeria, while other flowers that appear to be a single color reveal their nectar guides only under UV light. One example is Black-Eyed Susan, pictured above. The chemical compounds responsible for these patterns, flavonols, also absorb UV light, protecting the delicate reproductive parts of the flower from harmful mutations that might render a plant sterile.

Bees can see nectar guides from a distance, but these markings are less about attracting pollinators from far away than about telling them what to do when they arrive. The distinctive patterns, which can take the form of spots, streaks, or “bull’s eyes”, make pollinating activities more efficient. Pollinators can move quickly from flower to flower, making it more likely they will return to that same species if they have learned how to forage on it effectively. Studies have shown that nectar guides decrease the amount of time a pollinator spends per flower, which allows them to pollinate more flowers total, a bonus for plant and pollinator.

Nectar guides are also good for discouraging certain behavior, namely nectar robbing, which is when a pollinator takes food from a flower without “paying” for it. For example, if our native Valley Carpenter Bee cuts into the base of a flower and sips out the nectar without touching the reproductive organs, the flower won’t be pollinated. Since guides are generally on the inside of the flower, bees will tend to go in that direction first if they can fit inside the flower (Carpenter Bees are too big, so nectar robbing is their only choice for many flowers they encounter). Keep in mind that although nectar robbing is common, it doesn’t necessarily prevent pollination. Some theorize that flowers may be pollinated in spite of the bee not being directly inside the flower; “legitimate” pollinators are also forced further away to find another patch of flowers, preventing inbreeding of plants.

Not all plants have distinct nectar guides. Scent is another option for attracting pollinators; bees have a very strong sense of smell, 100 times stronger than us! Experiments have shown that bumblebees can carry the scent of anise (fennel) flowers back to their colony, and release it, along with their own pheromones, to give their sisters a clue about what to look for (they don’t necessarily do dances, like honeybees, to indicate where exactly the food source is).

Pollinators and plants make a good team, forming a mutually beneficial relationship in which each provides an essential service to the other. Nectar guides are integral to this relationship, an ingenious method for getting food to the bees and bees to the food. This process may be only partly visible to humans, but happy, well-fed bees can only be good news for us!

If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website.



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Caring For Your New Water-Wise Garden

Mulch conserves water and adds a finished look

This past summer, the California Department of Water Resources began offering rebates to San Joaquin County residents for replacing existing turf with edibles or ornamental water-wise perennials. These programs, along with a growing sense of ecological responsibility, have inspired many to move into a different genre of plants, leaving behind the familiar Hydrangeas and Bermuda Grass. If your garden has become a “terra incognita” of Deer Grass, Foothill Penstemon, and Texas Ranger, the absence of experience may cause you to revert to familiar watering, pruning, and fertilizing regimens. However, your new landscape may require a new mindset and different cultural practices to keep it healthy and beautiful.

Before you do anything else, get up close and personal with your plants. Determine each plant’s natural cycle throughout the year: Will it drop its leaves in winter? In summer? When does it bloom? Does it like full sun or part shade? Does it tolerate heavy soil? The learning curve is always high for newbies; this is normal, as is the “editing” a new garden receives to determine which plants are best suited to the quirks of your garden conditions.

Besides considering the conditions a plant needs to be happy, there are other aspects of water-wise gardening to think about:

Irrigation is one of the trickiest elements in any landscape, and a new water-wise garden may require you to rethink how you apply water. Many traditional landscape plants are thirsty in our climate, allowing a lot of fudge room for excess water. Low-water plants are not always as forgiving, as they are native to regions with little to no rain during the summer. Most will need some supplemental water, just not several times a week like your lawn did.

How much and how often to irrigate depends on many factors, including plant species, soil type, weather, and much more. Some basic principles include providing water to the entire root zone, and preferably just beyond, encouraging roots to grow outward. Extra water is necessary during the first 1-2 growing seasons to develop a healthy root system, which is essential for future drought tolerance.
See Yerba Buena Nursery’s webpage on plant establishment for more tips:

Mulch is essential to water-wise gardening. All mulches help retain soil moisture, though other benefits depend on the material. Organic mulches such as bark chips are best for most situations, providing organic matter, which improves soil structure. Succulent plants prefer gravel.

Getting the thickness of the mulch right is important as well. Thin layers provide no benefits, whereas thick layers can prevent rain water and oxygen from reaching the soil. Large bark chips (2” or more across) have a naturally porous structure, so a 3”-4” layer is good. Smaller chips and shredded materials are dense, so 2”-3” is about as thick as you want to go.
More information on mulching can be found at:

Pruning is a big topic. However, understanding your plants’ life cycles can tell you a lot about how to prune. Some pruning guidelines will be familiar: herbaceous perennials need to be cut to the ground; winter-deciduous species can be pruned during their dormant period. I recommend pruning water-wise evergreens (plants that retain leaves all year) after they flower, allowing time for pruning wounds to heal before the rains come to prevent stem rot.

Water-wise plants typically despise the shearing we foist upon traditional landscape plants such as Indian Hawthorn and Boxwood, which are better adapted to the excess irrigation necessary for this practice.

Fertilize your water-wise plants only if there is a severe deficiency in the soil. Plants that evolved in lean soils should grow at a moderate pace, so look for fertilizers with low analysis to avoid rapid, weak growth that attracts pests and shortens the plant’s life-span.
For help in reading fertilizer labels see the following website:

More tips on water-wise gardening can be found at
If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website at


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Keeping weeds under control

Last week I wrote about some of the weeds and invasive plants I have had to deal with. This week I will present some ways of dealing with weeds in your gardens. One of the most important ways to deal with weeds is to keep them from going to seed. Weeds produce lots of seeds per plant, often thousands to over 2 million in the case of purslane, a common garden weed. Unfortunately, land that has been left to the weeds like my vegetable garden was before I started gardening, builds up a weed seed bank in the soil.

These seeds remain dormant until changes in temperature, light, oxygen, moisture or other factors induce the seed to break dormancy and germinate when conditions are favorable for their survival. Hence seeds deep in the soil, with no light and perhaps no oxygen, remain dormant. However, with tillage to bring them to the surface they germinate.

Seeds on the soil surface typically have a much shorter lifespan than deeply buried seeds, because they are exposed to many organisms and processes that cause their death which include rodents, insects, soil-borne pathogens, UV radiation and other mechanisms. Deeply buried seeds of some weeds may remain dormant and viable for up to 60 years.

Another approach to control weeds in the garden and landscape is to irrigate to germinate their seeds and then remove them by a shallow cultivation. Doing this two of three times in the spring will greatly reduce weed abundance.

An approach which works in sunny gardens is to solarize the soil in July and August. The soil is thoroughly irrigated and UV resistant clear plastic is laid over the damp soil and sealed at the edges for 4-6 weeks to increase soil temperatures to about 140 ºF. This will kill nematodes, pathogens and weed seeds down to a depth of about 6 inches. Solarization will kill the seeds of some perennials like bindweed, but not their roots and rhizomes. Afterwards the soil should not be tilled deeply or new seeds from the weed seed bank will be brought up to germinate. Vegetables definitely thrive better after solarization as there are fewer pathogens and it enhances the breakdown of organic material to provide plant nutrients.

In the landscape, shade is the enemy of weeds so shrubs, groundcovers, and mulch will usually keep weeds at bay. Mulching to a depth of 3 inches not only saves weeding but conserves water as well. I am not a fan of landscape fabric having found it harmful to my rose garden’s health, but when I landscaped my wife’s studio, it was a necessary evil to keep bindweed at bay.

Bindweed (Convolvulus arvensis) is a perennial weed which reproduces by seeds, but once established comes back to haunt us every spring making it difficult to deal with. Bindweed is a Eurasian native that first invaded San Diego County in 1884. It has since become established throughout California below 5000 ft. It was declared the worse weed in the West in the first quarter of the 20th century. Roots can go 14 feet deep and roots and rhizomes from one plant may have many shoots above ground. For more information on dealing with this weed see:

Nutsedge can be controlled by diligently removing young plants before tubers are formed

Another perennial that is hard to deal with is yellow nutsedge (Cyperus esculentus). It produces   tubers on underground stems (rhizomes) that grow as deep as 8 to 14 inches below the soil surface. Most tubers occur in the top 6 inches and these tubers can form new plants. If tubers are not retained when dug out with the plant, buds on the tubers sprout and grow to form new plants.

Tubers rather than seeds are the main source of new plants. Removing young plants with 5 to 6 leaves before they develop tubers is a smart way of eliminating this weed. This requires a lot of diligence and persistence. It can be a problem in lawns and landscapes as well. Nutsedges will emerge through bark or rock mulches and I have seen them penetrate landscape fabric as well. For more information on nutsedges see:

As a last resort there are some herbicides which may help control weeds in some places and circumstances, but not in food growing areas or around roses or other ornamentals that are highly sensitive to some herbicides. Glyphosate has been listed as probably causing cancer by the World Health Organization, so use with caution. More information on weed control and benign herbicides can be found here:

If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website:

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Weeds and invaders-the gardener’s nemesis

It was a fairly wet winter here with 16 inches of rain so far. Consequently, weeds have done well and I am fighting hard to get things under control. Common Mallow (Malva neglecta), Redstem filaree (Erodium circutarium), barley foxtail (Hordeum jubatum) which also could be named the veterinarian’s mortgage lifter, field bindweed (Convolvulus arvensis), scarlet pimpernel (Anagallis arvensis) and yellow nutsedge (Cyperus esculentus) seem to be everywhere and my garden in particular shows inadequate weeding.

My mother’s definition of a weed still works for me. A weed is a plant you don’t want. It is a plant in the wrong place. It could be a rose in your corn patch or a corn stalk in your roses, but if you don’t want it there—it is a weed. But the agriculturist’s definition is: a valueless plant growing wild, especially one that grows on cultivated ground to the exclusion or injury of the desired crop. That definition can work for gardeners too.

A good example is the violets which I love in my lawn and landscape but not in my strawberry patch. I have one old strawberry row that I had intended to rototill under, but I never got around to it and now it is invaded by violets. Strawberries are present now so rototilling will need to wait until I am done eating them.

I have played ‘whack a mole’ with weeds for years it seems. I have dug out nutsedge roots and tubers and have come to agree with the adage that the only way to get it out of your life is to sell the farm, but, unless you move to an apartment, it will likely be at your next place too. Alkali mallow or Sida Mallow (Malvella leprosa or Sida hederacea, depending on your favored taxonomist) is another persistent perennial weed that comes back each year though I cut it off each time it comes up, I cannot kill it because it has deep roots that I suspect are all from one underground root system as is the case with bindweed.

At one of our Master Gardener training sessions on weeds, the instructor informed us that he controlled bindweed by whacking it every time it reared its face and after 2 years eliminated it by starving the root.  Hence, I have tried that approach, but my problem seems to be a garden much larger than the instructor’s.

In the turf areas I pretty much tolerate all manner of plants with the one exception of dandelions. They are fine except for the fact they bloom fast and release seeds that soon become more ‘bloomin’ dandelions. Being perennial, they come back year after year to bloom again. Another ‘whack a mole’ plant to deal with.

In my landscape I have some plants that have naturalized and are impossible to eradicate.  One is Bermuda buttercup (Oxalis pes-caprae) which is a South African bulb now common to inland and coastal landscapes in winter and spring. The flowers are pretty but it is everywhere. At least my chickens like to eat it.

Some of my invasives are no doubt on the ‘please do not sell list’ handed out to nurseries by Plant Right, a non-profit San Francisco group ( ) that works with retailers to prevent invasive plants from making their way from nurseries to our gardens. One on their list is Periwinkle (Vinca Major), an ornamental that, like Bermuda grass, is very invasive. According to UC IPM website, species that rapidly colonize an area are often called exotic invasives. The important biological difference between invasive plants and garden weeds is the ability of invasive plants to disperse, establish, and spread without human assistance or soil disturbance. Because of this, they are much more problematic in natural environments than are typical weeds. Shade tolerant Vinca major has taken over large areas under redwoods on the north coast and it is trying to take over my landscape, but so far I have kept it stymied for 40 years, but not eliminated.

Another invasive that has naturalized in my landscape is Italian arum (Arum italicum). It multiplies by seed and bulblets, so I pull all the seed stalks each year, but the bulbs are difficult to deal with effectively. Covering them with a board for 2 years can work, but that is hard to do a big scale. I see this Arum advertised in nursery catalogues and wince at the garden misery it will bestow on the unlucky buyer.

The year is young and crabgrass, pigweed, lambsquarter and others will be germinating soon to keep gardeners like me off the streets and out of the bars. Happy weeding!

If you need help identifying weeds or suggestions for controlling them, this IPM website will help:

If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website:

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Three Water-Wise Plants for Summer Color

With our spring temperatures already rising at times into the mid- to high-80s, this summer promises to be another hot one. Even the hardiest gardeners try to escape the worst of our midday Central Valley summer heat and the punishing sun. Yet while we might wilt, some plants keep plugging along and even thrive under such tough conditions.

Here are some beautiful and unique plants that—once well-established—can handle low-water conditions and summer heat and still provide long-lasting summer color.

Russian Sage (Perovskia atriplicifolia)

The common name of this plant is strangely misleading: it doesn’t come from Russia (it’s native to south-central and southwestern Asia) and it’s also not a true sage (but like others in the Salvia genus, it does belong to the mint family). It’s a vigorous, heat-loving plant adapted to well-drained, nutrient poor soils, producing numerous, upright, 3- to 4-foot-tall stems with a fine-textured, feathery appearance. The foliage is grayish-green, pleasantly aromatic, and pest-resistant; the tiny, fuzzy blooms are lavender-blue and appear in long sprays at the ends of the stems.

This plant is wonderful for a pollinator-friendly garden, since it attracts honeybees, butterflies, and other beneficial insects. It’s also an excellent selection for the back of a perennial border, especially since it’s partly deciduous and should be cut down nearly to the ground in late winter or early spring.

The most common Russian Sage cultivar is the award-winning ‘Blue Spire.’ Another excellent selection is Silvery Blue Russian Sage (P. atriplicifolia ‘Lissvery’), which has silvery leaves, a smaller mature size (up to 20 inches tall), and flowers from mid-summer until fall; it appears on the UC Davis Arboretum’s “35 Low-Water Plants” list. Yet other great performers are the compact cultivars ‘Lisslitt’ and ‘Little Spire,’ which grow only 1½ to 2 feet tall and don’t flop over, and ‘Lacey Blue,’ with large blue-purple flowers.

Marshall’s Oregano (Origanum ‘Marshall’s Memory’)

This is an unusual and highly ornamental oregano that—unlike culinary oregano—also produces pretty flowers. It’s a tough, heat-loving plant that will even tolerate south- and west-facing exposures. This stunning herb is one of the plants included on the UC Davis Arboretum’s “Durable Delights” plant list.

This type of oregano only needs deep watering once every couple of weeks. It can be grown either in well-draining garden soil or in pots. The pruning needs of this plant are minimal; to renew, simply cut it back almost to the base in winter.

Marshall’s oregano produces bright green early spring growth, which develops into a low-growing (under 1 foot tall) mass of medium green, scented leaves. The long-blooming plants are covered from summer to fall with tiny, delicate flowers ranging from deep pink to reddish-purple. Butterflies are attracted to the nectar in the flowers, and the flowering stems can be used for dried flower arrangements. Simply harvest the blooming stems when most of the flowers have colored but before they begin to dry at the base, then bundle the stems together and hang them indoors for a few days to dry.

Coronation Gold Yarrow (Achillea ‘Coronation Gold’)

This low-water-use perennial plant is excellent for use in hot-summer climates. It’s a tall-growing plant (up to 3 feet high) with delicate-looking, deeply-cut, greenish-gray leaves and tiny, bright golden-yellow flowers borne in flat-topped clusters. (A similar variety called ‘Moonshine’ is shorter, with lemon-yellow flowers and grayer foliage.)

This yarrow thrives in summer sun and can tolerate many types of garden soils, including clay. It’s reliable performance, brilliant show, and minimal maintenance requirements have earned this plant a spot on the “Durable Delights” plant list.

Coronation Gold Yarrow begins blooming in early summer and continues for several weeks. Unlike many other yarrow varieties, it is sterile, and will not reseed itself in the garden. Beneficial pollinators visit its flowers for both their nectar and pollen. The blooming stems can be cut for use in fresh flower arrangements; they also superb for dried arrangements if harvested just before the flowers fully open and then hung to dry.

For gardening-related questions, call the UC Master Gardener office at 209-953-6112, or use our website:

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It’s Time to “Celebrate Spring!”

This is the time of year when gardens burst into full glory, with plenty of fresh spring growth, gorgeous blooms, and wonderful scents! (My enthusiastic note is tempered with a sympathetic nod to allergy sufferers, for whom this beautiful time of year can also be the most miserable.)

The show this season is even lovelier than in past years, thanks to our more normal winter rainfall and periodic spring showers. It’s a perfect time to get out and enjoy the colorful sights in your own garden and in your local surroundings.

If you’re looking for a fun and scenic little adventure without having to travel far, plan to attend an upcoming event presented by the San Joaquin County UC Master Gardeners: the 2016 Garden Tour. The theme of this year’s tour is “Celebrate Spring!”

The tour (a biennial event) will be held on Sunday, May 1 from 10:00 a.m. to 4:00 p.m. at various locations within the city of Stockton, and it promises to be an enjoyable, inspiring, and informative event.

This year’s garden tour features seven privately owned gardens and one public garden with three distinct areas, all in central Stockton for convenient access. Here’s a list of some of the many garden elements and features you can expect to enjoy during the tour:

  • A water-wise garden incorporating color, form, texture, and artificial turf
  • A lush and shady garden with an Asian flair
  • A scenic, woodland-type garden with a pond and expansive views
  • A terraced, bird-friendly back yard with garden art and an herb garden
  • A highly varied garden with entertainment spaces and whimsical features
  • A bountiful organic garden filled with vegetables and numerous fruit trees
  • One public garden that highlights different plant types: edibles, roses, and valley-appropriate California natives

In addition to the sheer enjoyment offered at each location, there will also be many educational resources available to tour-goers. Certified UC Master Gardeners will be available at each site to lead demonstrations, explain displays, and answer gardening-related questions. Free educational handouts relevant to each tour location will be provided. Important plants within each garden will be labeled with common name, scientific name, and cultural information for the benefit of visitors. Various University of California horticultural publications and San Joaquin Co. UC Master Gardener journals will be available for purchase either by cash or check.

Tickets to the 2016 Garden Tour are only $20.00 each if purchased in advance. The cost increases to $25.00 apiece if you buy tickets on May 1, the day of the event; all ticket purchases that day must be made at the University of the Pacific, Robb Family Garden, 1081 W. Mendocino Avenue.

Garden Tour tickets can be bought directly from the UC Master Gardener program in two ways:

  • At the UC Master Gardener Office, 2101 E. Earhart Avenue (off of Arch-Airport Road near the Stockton Airport). The office is open Monday through Friday from 8:00 a.m. to 5:00 p.m.
  • Online by credit card at the San Joaquin County UC Master Gardener website: April 24 is the last day to purchase tickets online and have them mailed to you. Tickets purchased online after April 24 will be held at a will call table at UOP’s Robb Family Garden (address above).

Tickets will also be available for purchase (cash or check) from UC Master Gardeners on April 23, 24, and 30 from 10:00 a.m. to 2:00 p.m. at two local nurseries:

  • Delta Tree Farms, 12900 N. Lower Sacramento Road, Lodi
  • Quail Lakes Nursery, 3404 Shadowbrook Drive, Stockton

Once you purchase tickets, you’ll receive a detailed brochure listing all the garden locations and their major features. The brochure also includes a map for general navigation. Light refreshments and water (for refilling personal water bottles) will be available at select garden sites.

Treat yourself to an inexpensive and fun day, and help support a valuable cause! Proceeds from the 2016 Garden Tour will help fund UC Master Gardener education and gardening outreach activities in San Joaquin County.

For gardening or tour-related questions, call the UC Master Gardener office at 209-953-6112, or use our website:


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Irrigation Tips for Water-Wise Gardens

Orchid Rockrose is a drought-tolerant, evergreen shrub with large, pink flowers in spring. It is widely available and easy to care for.

If scheduling irrigation were as simple as peeking out the kitchen window to see if things “look dry”, the Master Gardener program would barely be able to justify itself. Most of the problems we encounter stem directly or indirectly from water-related issues, especially with so many drought-tolerant plants and their mysterious water needs popping up all over town.

Drip irrigation has become very popular, but like any other cultural practice, must be done correctly to be effective. Because root systems are much larger than most people realize, a common mistake is to place one drip emitter next to a new plant and walk away forever, never adding new emitters to expand along with the ever-expaning roots. It’s important to encourage this expansion, which is key to the plant’s tolerance of drought.

Irrigation should be sufficiently deep (and wide) so that the entire root system is hydrated. Exactly how deep depends on the plant: ornamental grass and herbaceous perennial plant roots are in the top 8-12”, and the majority of shrub and tree roots are in the top 18-24”. A tool such as a screwdriver or trowel will allow you to check soil moisture several inches down. Scheduling will depend on many factors such as the time of year, your soil type, whether you have drip or pop-up spray, and the flow rate (measured in gallons per hour for drip and per minute for spray). Running drip for 10 minutes will barely wet the top 1/2” of soil, encouraging roots of ornamentals to grow right near the surface, making them more prone to drought. Help with drip irrigation can be found on the Sonoma County Master Gardener’s website:

Many water-wise plants do quite well on 2-3 deep waterings a month after a couple of growing seasons to get them established, but you will have to experiment to find the best schedule for your site conditions. Soil should be allowed to dry slightly between waterings for drought tolerant plants, though never to the point it becomes dusty. Bare soil can form a water-repellant “crust” on the surface, which increases run-off from irrigation (and rain); applying a 3-4” layer of organic mulch such as bark to the soil surface will both prevent this crust and retain more soil moisture.

What about California native plants? They evolved in our climate, so why should you water them at all? This seems logical enough; unfortunately, native plants are dependent on a compatible soil environment to hold and deliver this water to them. Decades of human activities have completely changed this environment, meaning no one has native soil, and everyone must provide at least some supplemental irrigation. Other factors contributing to the need for irrigation include groundwater depletion, less than average rainfall, and the fact that most homes are built high above grade so rain washes down gutters rather than recharging the local aquifer.

There are a small number of natives that do not require any supplemental irrigation, but they are accompanied by a strict requirement for excellent drainage. If working with your sandy soil is like a trip to the beach, go ahead and try xeric plants intolerant of heavy soil such as Flannel Bush (Fremontodendron californicum) or Woolly Blue Curls (Trichostema lanatum); Stocktonians are more likely to build bricks than sand castles with their soil, so it’s better to stick with less fussy plants that require irrigation now and again.

Improving drainage will increase rainwater percolation into your soil, which acts as a reservoir for the dry months, thereby reducing irrigation needs. The best way to achieve this is to improve soil microbial life by lightly mixing a 1” layer of compost into your soil and applying an organic mulch to the surface (do not mix it into the soil). You can also install a rain garden, which is basically a depression in the ground that gives rainwater a place to linger while it percolates into the soil. Plants selected for this area can take seasonal flooding but do not require as much water in the dry months. See this link for more details:

With all this talk about water-wise plants needing irrigation, you might be worried about not watering them enough, which brings me to my last point: you can definitely overwater water-wise plants, and unlike species adapted to wetter climates, they will not be as forgiving. Soil biology is easily altered by temperature and moisture, and certain pathogens thrive in hot, damp soil that water-wise plants never developed resistance to. You may see them initially growing faster with extra water, but don’t be fooled; this rapid growth is likely to be weak and susceptible to pests, and the stress of those soil pathogens will probably shorten the plant’s life considerably. Keep in mind that wilting leaves can be a sign of both over- and under-watering; the best way to know what’s happening is to check the soil. If it’s soggy, let the soil dry out a little before watering again.

If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website:

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What You Need To Know About Landscape Fabric

Landscape fabric never stays in place

Many products claim they can end your weed woes. One such item is landscape fabric, a semi-permeable material made of woven polypropylene laid directly on the soil. For areas to be planted, slits are cut into the fabric where plants are to be placed.

Please don’t be fooled by the fix-it-all façade of this infamous product. Although landscape fabric offers some weed prevention, there are many long-term factors to consider:

The weeds will be back, even if you sprayed with herbicide, and they will be even more difficult to remove when their roots intertwine with the fabric. Landscape fabric can block some weeds, but others will germinate from underneath, or in soil that gradually collects on top.

Polypropylene is non-biodegradable. Unfortunately, this does not mean it will stay completely intact forever. Eventually it will break up into irritating shreds without any benefits to the soil.

Soil life is inhibited. Organic mulch placed on the surface will provide few soil benefits when there is fabric in the way. Fungal threads residing in soil that normally grow up into mulch for decomposition act as a “glue”, keeping mulch in place. Landscape fabric blocks this natural process, causing a “mobile mulch” effect, wherein bark is blown away in dry weather and floats away in storms. Air circulation is also reduced, which is another death-blow to soil organisms. If you have had landscape fabric down for years, you will often find sickly pale-colored, rock-hard soil underneath, signs of soil lacking in abundant life.

Slower rain percolation happens when the soil becomes dead, hardening into an impermeable medium turning rainwater into run-off. With rain being so scarce, it’s important to capture this precious resource on-site to help recharge the aquifer.

Applying fertilizer and compost is difficult because you have to pull back the fabric to apply anything and then put it back down again. Who wants to do this every year? Of course, the lack of oxygen destroys the soil life necessary for utilizing these amendments and making nutrients available to your plants, rendering compost and fertilizer moot.

Roots are unhappy because they cannot grow well in soil lacking microbial life and oxygen. The only air and life is near the surface, which is where you find shrub and tree roots after a few years under landscape fabric. Roots close to the surface are much more prone to drought stress than deep-rooted ones. This can be combatted by placing drip irrigation under the fabric, but keep in mind the difficult in inspecting and maintaining a system that is essentially buried.

It’s ugly. Eventually your garden will look like a discount bin of of frumpy, black shirts half-buried in dirt. Mulch is often used to cover landscape fabric, but what’s the point of having both? Frumpy fabric won’t provide any weed prevention (unless you have weeds with fashion sense). Using 3″-4″ of organic mulch alone is better in the long term.

Landscape fabric is required under gravel pathways and in drainage installations, where permeability is desired, but soil health is not important. There will still be some weeds, but this is unavoidable in any case, no matter what advertisers say! Even if you are not convinced to avoid placing landscape fabric under your plants, avoid using plastic sheets under ornamentals, as the problems listed above will be multiplied tenfold, particularly when it comes to aesthetics and soil health.

Alternatives to weed control often involve changing cultural practices, though it always depends on what the problem is. Whether you are battling a few Dandelions or a platoon of Yellow Star Thistle, begin by properly identifying the plant(s). See the UC Integrated Pest Management website for advice on how to deal with different species:

Weed management queries and other gardening related questions can be directed to the UC Master Gardeners at 209-953-6112. More information can be found on our website:


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Make garden space by growing upward

A metal pyramid hosts a Mandevilla 'Alice Dupont'

Back yards in today’s subdivisions tend to be on the small side, though I have lived in a couple of homes built in 1912 that had small back yards as well. Of course gardens don’t need to be limited to back yards as the trend is to make every part of the property bloom with plants other than lawn. However, as gardeners we have to make do with whatever our garden spaces are. One way to cope with limited garden space is to grow upward using trellises or other techniques.

If you are growing grapes, black berries, kiwis, luffas, chayote, pole beans, peas, cucumbers, tomatoes, cantaloupe or Dahlias, it is either necessary and/or possible to grow them vertically on trellising, stakes or cages.  Of course growing cantaloupes on a trellis is a little tricky in that melons need to be supported by slings attached to the trellis.

Trellises can be made from lots of material.  Wood, bamboo, PVC pipe, scrap metal, iron or copper pipe, old netting, or woven wire fencing can all be pressed into service.  If using wood, cedar, cypress, redwood or other rot resistant varieties are best. The kind of material and stoutness depends on the plants involved. For example, if you are trellising kiwis, you will need a substantial trellis, perhaps of steel pipe, as the crop from a single kiwi plant can weigh over 200 lbs.  Similarly, Wisteria vines can be stout and vigorous requiring a strong structure.

Trellises for beans, peas or sweet peas can be wire, string or netting. I use old sheep fencing that I attach to stakes for my peas. For beans I use an old modified swing set which is strung with sisal twine that works quite well. However, a simple teepee built of wood can also be used for beans and peas. A chayote trellis also needs to be stout for a heavy crop and I repurposed some old steel 2 inch well pipe for mine.

Tomatoes are best when caged or grown on a trellis to keep fruit from the molds and other destroyers lurking on the soil. There are several approaches that work for tomatoes and the one I prefer is to make cages from concrete reinforcing wire or heavy woven wire. Cages that are about 6 ft. tall and 18-20 inches in diameter are good for indeterminate varieties like Ace and Early Girl which can top 6 ft.  If you are growing determinate types like Shady Lady, Roma or Celebrity, a 3.5 ft. high cage will work. If you are lucky, you might find a commercial tomato cage that works, but I have had little luck.

Many flowers also grow upward. Large, fragrant evening-blooming moon flowers can be trained on string to fences, posts or a trellis. Climbing roses, sweet peas, Passion vine, Mandevilla, Clematis, Wisteria, Honeysuckle, morning glories and trumpet vine all require something to climb on. My Chinese Wisteria is on a trellis fashioned out of old pipe that was lying around the homestead. I also have a Japanese Wisteria trained as a tree, supported by a steel stake. There is also the option of letting vines such as Clematis and morning glory climb on shrubs or trees.

A Japanese Wisteria (floribunda) trained as a tree with a steel stake for support.

I have two trumpet vines (Campsis radicans) which are very attractive to hummingbirds. One is fixed to a 14 ft. post in my yard and the other is growing on an old walnut tree and has been there for over 50 years. It blooms in the top of the walnut and drops spent, attractive flowers on my patio each summer.

We can also espalier fruit trees along a south facing fence or wall, creating a more two dimensional effect to conserve space for other plants. Pears and Apples lend themselves well to espalier but stone fruits such as plums, apricots and peaches on dwarf rootstocks can also be trained with proper attention to pruning.  It may take more time to train these plants, but it is a challenge that is rewarding with tasty fruit from a small space.

To provide a place to climb can be also be an opportunity to use or fashion some art in the garden. I have built 3 pyramidal trellises from scrap steel. They have a rustic, artsy look to them. One of them hosted a Mandevilla ‘Alice DuPont’ this past summer and the other one a Clematis.  Since not everyone can weld, it is also possible to make attractive pyramid trellises using wood. Whatever your whimsy or your medium for trellising, have fun growing up.

A note for gardeners: Delta College has plants for sale on Fridays from 10 AM to 3 PM at their greenhouse. On April 16th from 9AM to 3PM, Linden Community Garden Club has its annual plant sale at the Methodist Church in Linden, features herbs, tomatoes, peppers, perennials and many other plants.

If you have a gardening related question you can contact the UC Master Gardeners at 209-953-6112. More information can be found on our website:


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    Lee Miller

    Lee Miller is a University of Delaware graduate and retired fisheries biologist, he gardens on 10 acres and makes wine each year with the help of a cadre of friends. However, his first love is gardening and he grows various fruit trees, heirloom ... Read Full

    Marcy Sousa

    Marcy Sousa is the San Joaquin County UC Master Gardener Program Coordinator. She is a Stockton native and enjoys teaching others about gardening. She has her bachelors from Stanislaus State in Permaculture. She has been with the program since 2007. Read Full

    Nadia Zane

    Nadia Zane is a UC Master Gardener, a landscape designer and Stockton native. She has a fondness for California native plants and sustainable landscaping, which she utilizes in her work for Native Beauty Garden Design. She is a member of the CA ... Read Full
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