Dahlia Growing Information
Planting:
If you have purchased dahlia tubers, if it’s too early to plant them, you may wish to place them in a ziploc-style plastic bag with the wood shavings in which they were received. DO NOT seal the plastic bag; leave the top open to moderate humidity. Keep this bag in a cool, dark place in your home until you’re ready to plant. If your tubers look a bit wrinkly, don’t worry, they will still grow! A very light mist can help if the tubers are getting too dry.
Dahlias grow and flower best in a well-drained, sunny site. They like warm weather and will not tolerate frost. Plant dahlia tubers outdoors after your last frost date (typically the first weeks of May in the Okanagan), when the soil has warmed. Most dahlias will flower from August until frost.
To plant, dig a 6-12” (15-30cm) deep hole and amend the soil with compost. If the soil drains poorly, mix in some fine gravel. Backfill the hole with the amended soil and plant the tubers 2-4” (5-10cm) deep, and about 1-3’ (30-100cm) apart, depending on the final size of the variety. Tubers may be watered in at planting, but to prevent the tubers from rotting, minimal water should be provided before green growth shows above the soil. Growth begins in 14 to 20 days.
Growing:
Tall varieties, such as dinnerplate dahlias, may need support or staking to keep the heavy blooms from falling over. To create a bushier plant with more flowers, you can pinch off the top growth of the dahlia shoots above the third set of leaves while plants are still young.
Fertilize dahlias monthly with a water-soluble, organic fertilizer that is formulated for flowers. Avoid using a high-nitrogen fertilizer, or you'll get lots of green growth but few flowers. You may wish to mulch with straw or shredded bark to reduce weeds and retain moisture. Once growing, dahlia plants will need to be watered regularly. Feel free to cut blossoms for indoor flower arrangements and remove old blossoms to encourage more branching and flower production. Although they have a relatively short vase life, dahlias are some of the most beautiful cut flowers.
Overwintering:
In the Okanagan, dahlia plants are annuals, and tubers left to overwinter in the ground will freeze and die. If you would like to enjoy your dahlia plants year after year, the tubers can be dug up and overwintered.
In fall, after the first frost has blackened the foliage, cut off all but 2-4” (5-10cm) of top growth, and carefully dig tuber clumps without damaging them. Allow the clumps to dry for a few days in a frost-free location, out of direct sunlight. Once dry, remove excess soil and use sharp pruners or flower snips to remove damaged tubers from the clump. If you want to increase your stock, you can also divide the clumps; just make sure that each tuber or clump of tubers has at least one eye or it will not sprout next spring.
Store tubers in a ventilated box or basket. Fill the box with slightly moistened sand or vermiculite and place it in a cool, dry location. Don’t let your tubers freeze! The ideal temperature for storing tubers is 4-7° C (39-45° F). Check tubers periodically through winter for rotting and drying out. If the tubers appear shriveled, mist them lightly with water. If any start to rot, trim and dispose of the rotted portion of the clump so it won't spread. When warm weather arrives, you can plant the overwintered tubers and begin the cycle again.