Growing Dahlias is hard work but very rewarding.

I have grown dahlias for a lot of years and I am still learning how to be successful at propagating this plant from tubers. Dahlias come in various nuances of colors, sizes, and forms and they bloom starting in June continuing to November. Last year I had about 150 Dahlias. They are a bit perplexing and difficult at times, but the rewards are so great that the effort to deal with these cantankerous tubers is worth it.
One good thing about living in California, you don’t have to dig your dahlia tubers to keep them from freezing like my mother used to do where I grew up in New Jersey. My mother only had a few dahlias and perhaps digging a few and storing them in the cellar each year was enough of a workout.
I am hard-pressed to dig all the dahlias that I grow. Last year I dug all of them, but this year I dug only half. It is a chore to wash off the black adobe clay from the tubers, label and store them in wood shavings until this spring when they will be divided to replant or give away. Dahlias tubers left in the ground over the winter are well established and know when to start growing and they bloom sooner than newly planted tubers. If you like early blooms, and who doesn’t leave some in the ground. The downside of not digging them is that some may rot if the winter is particularly wet which is not the case this winter. Hence I am hoping that the four rows I didn’t dig will be blooming early.
Tubers should be planted 2-3 feet apart with 4 feet between rows to allow access. They will need to be staked and tied as they grow, so best to plant the stake at the same time that the tuber is planted so the tuber is not impaled by the stake if done later. Tomato cages can also be used to confine the plants. I like to mix compost into the planting hole which enhances growth without chemical fertilizers. Just planted tubers should not be watered heavily but once plants are growing about 1 inch of water per week is good. I use a drip system with 2 GPH emitters and water for an hour every other day or about 6 gallons per plant per week.
Unfortunately, there are always pests lurking to ruin your dahlia garden. When the first shoots appear they are food for snails, slugs, and earwigs. These pests can be thwarted by using snail and slug bait. If you have pets the best bait contains iron phosphate which unlike metaldehyde baits will not harm your pets. You can also deplete the population by hunting them by flashlight at night. Earwigs can be thwarted by placing some diatomaceous earth in a ring around the young shoots or they can be trapped using tuna fish cans or cat food cans with ¼ inch of oil preferably fish oil in the bottom with the cans buried at ground level. It is also a good idea to deny them hiding places beneath boards or mulch if possible.
Later in the season, the pests are thrips and spider mites. When you want to enjoy the blooms these critters want to enjoy the dahlia leaves. I found that spraying the foliage with water helps control their abundance as mites don’t like moist conditions and they along with thrips can get washed off. Insecticidal soaps and Neem oil solutions can also be used. It is good to stay on top of this or the plants will suffer and blooms will be less too. It is also good to keep a sticky trap in the garden to monitor for thrips abundance and keep on top of it. For more information on pest control see: http://ipm.ucanr.edu/.
Keep flowers deadheaded or preferably your vases full. To encourage larger blooms it is good to disbud the two side buds and leave the main bud. It also a good idea to head cut the new plant at 12 inches to encourage early-branching which will result in more blooms later. It is also good to thin older well-established dahlias if there are many weak shoots they should be removed to enhance energy going to the main stems.
More info and videos on dividing and storing Dahlias is at Swan Island Dahlias at: http://www.dahlias.com. Happy dahlia gardening.

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: http://sjmastergardeners.ucanr.edu/CONTACT_US/.

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