Dazzling Dahlias and How to Grow Them
Dahlias are a family of flowers known for their tall, ultra-vibrant blooms that are popular for cut flower arrangements. Most varieties have voluminous, pompom flower heads with satisfyingly symmetrical petals, but others are flat like daisies or have layers of petals in contrasting colors and shapes. They’re native to Mexico, and while most regions in the United States can only grow them as annuals, our climate is warm enough to grow dahlias as perennials, provided we use proper winter protection. Here’s how you can grow them yourself for a garden bursting with summer color and gorgeous cut bouquets!
How Long Do Dahlias Bloom?
Dahlias typically begin to bloom in late spring, and with the proper techniques, you can encourage them to keep blooming for up to five months! How do you make dahlias bloom for a long time? The trick is to deadhead the spent blooms. Deadheading will stop your plant from directing its energy toward keeping those old flowers alive and instead will focus on producing a fresh set of blooms.
Growing Dahlias: Seeds vs. Tubers
While you can technically grow dahlias from seeds, it takes a lot longer that way, so we recommend planting tubers instead. In colder climates, people plant dahlias in spring; then, once they’ve finished blooming, they’re dug up and safely stored over the winter so you can replant them in the following spring. However, in California, we can leave the tubers underground over the winter as long is the area is not over-irrigated. It helps if you spread a generous layer of mulch across the soil surface to help insulate the tubers from dipping temperatures.
Unlike spring-blooming bulbs and tubers that you plant in winter, summer-blooming flowers like dahlias are planted in spring once temperatures begin to rise. While it certainly is not common to encounter frost in California, the weather has been unpredictable in recent years. So, if you’re getting ready to plant your dahlia tubers, make sure there aren’t any upcoming cold spells or freak storms in the forecast.
Planting Dahlia Tubers
Six weeks before planting, loosen up the soil 12 inches deep, and mix in plenty of fresh compost, as well as some balanced organic fertilizer. When it’s time to start planting, plant your tubers six inches deep, with their “eyes” facing upward. Depending on your chosen variety, your dahlia tubers should be 2-4 feet apart, so double-check the planting instructions before going ahead.
After planting, water generously and spread a layer of bark or shredded wood mulch across the soil surface; this will help retain soil moisture and stop weeds from germinating. As summer progresses, you’ll want to top up your mulch with a fresh batch, as it naturally breaks down, enriching the soil below over time.
As your dahlias grow tall, you’ll want to prevent them from falling over. To keep them upright, stake the stems once they reach 12 inches. Each dahlia can grow more than one stalk, but if you want the biggest, brightest blooms possible, it helps to pinch off any extra shoots.
Fertilize your dahlias again in July with a balanced organic fertilizer labelled for flowers or roses. Remember to deadhead those spent blooms once they fade—this will help encourage repeat blooming! Once fall comes to an end, and your dahlia has finished blooming for the year, cut back the foliage to 3 inches high, then apply a thick layer of mulch.
There are so many incredible dahlias for sale in California, and if you do decide to plant them this year, you’ll be amazed by how long they bloom. Visit Roger’s Gardens to see all our top picks for 2022!
For more information, check out our videos Lew Whitney's Secrets to Growing and Maintaining Dahlias and How to Grow & Maintain Dahlias with Steve Hampson.