It's time to plant dahlia tubers! Like anything really spectacular in the garden, growing dahlias takes some special effort. It's taken me a few years to get the hang of it, but I'd like to share a few tips that made all the difference in my level of success here in zone 8 in Southern Oregon. I struggled for a while because our climate is hot and dry in the summer and dahlias, being native to the mountains of Mexico, like a more moist and moderate climate. My primary obstacles to sucess initally were soil fertility, drought, tuber, stem and flower pests, and trellising. So, here's what I do now to address those and other important steps in the growing process:
Plant Early. If you can start your bulbs in a greenhouse, I recommend planting your bulbs in 1 gallon pots (if you can’t, plant just when danger of frost has passed). Fill your pot nearly full with soil and place bulbs in the pot near the top with any “eyes” that you see facing up. Dahlia eyes are reminiscent of potato eyes. Cover lightly (1”) with soil and water deeply to begin. But don’t overwater while they’re in the pots as they can rot! After that initial watering let the soil surface dry out before you water again. I start my dahlia tubers in the greenhouse in April, 4-6 weeks before our last Spring frost. This early start under cover allows me to beat the slugs in the field because, by the time I plant them out, the dahlias have enough growth to withstand slug predation. Also, a dusting of diatomaceous earth (D.E.)when I plant them helps deter the slugs who do show up. If I'm overhead watering, I reapply the (D.E.) regularly.
Plant Into Fertile, Well-Composted Soil. Or plan to regularly fertilize your dahlias. I give plants a liquid drench of seaweed or fish tea weekly during their bloom period if I’ve planted into less fertile parts of my field. Well-balanced fertility will lead to healthy plants that are more resilient to pests. Water deeply and regularly during both the vegetative and blooming stages.
Pinch. This is the key to more plentiful stems on your dahlias. At 8-12 inches, pinch back the center growth tip by making a clean cut with sharp snips. The dahlia will recover with multiple side branches that lead to more flowers. Sometimes dahlias will have 2-3 robust stems instead of a single one; pinch back all of these. It’s hard to do at first, but worth it in the long run!
Exclude Pests. If you can’t stand to see little bites stolen from your perfect dahlias, I recommend bagging blooms with mesh “organza” bags. It sounds tedious, but it’s way more effective than any organic spray, and once you get the hang of it, about as fast. Put these on just as buds begin to grow plump. Then, have a plan for gopher control. Plant in an area of your garden where you don’t see gopher activity, or be ready to trap. It’s also possible to plant into DIY cages made from hardware cloth. Just remember, if you’re dahlias are really thriving, they could produce 6-12 tubers the same size that you planted, so make your cage big enough to let them grow as big as they’d like. Also, I lift my dahlias in the fall (after our second frost) and store them in the winter to protect them from critters.
Stake Your Dahlias. On the farm we trellis the dahlias horizontally with Hortonova brand netting, but they can also be staked individually or corralled as a group with t-posts and string running the perimeter of your beds. Do it early!!! It’s no fun to try to stake a blooming dahlia after it has already fallen.
Harvest. Hurray, this is the very exciting moment you’ve anticipated so hopefully. When you make cuts, go deep! Taking a long stem, even if you wind up cutting off some smaller side buds, encourages the plant to make more long stems. It will likely result in a larger abundance of flowers too. If you don’t regularly harvest for bouquet making, plan to deadhead spent flowers. Deadheading is vital for promoting the plant’s creation of new flowers.
≈ by Stacey Denton