A quick guide to growing dahlias in Okanogan County and the Inland Northwest.
Location.
Select a location for your dahlias that receives at least 6 to 12 hours of sunlight. Dahlias grow best in full sun, although in our hot dry climate, some afternoon shade can help the blooms to last longer.
Planting.
Dahlias do best in neutral soils with a pH between 6.5 and 7. We generally have alkaline soil in the Okanogan, so it may be best to amend soil to correct for high pH. A soil test will identify potential issues with pH and recommend fertilization needs.
It is best to plant dahlia tubers after all danger of frost has past (the same time you would plant tomatoes). It definitely varies by year, but plan for ~May 15-ish. Memorial Day is a safe bet.
Dahlias can grow tall and have large flowers so they require staking. It is best to install the stake at the time of planting to avoid damaging the tuber or roots later. Dig a hole 4 to 6” deep and pound a 4’ piece of rebar into the ground on one side. Lay the tuber on its side with the eyes pointed upward at the base of the stake. If the dahlia tuber started sprouting and the sprout broke off, don’t worry, it will grow another. Tomato cages also make excellent supports for smaller dahlias. Spacing between plants is generally 2′, but you can plant 12-18″ apart with smaller growing varieties.
Unless the ground is extremely dry, do not water the tuber until foliage extends above the surface. The most common reasons for dahlia tubers to rot before sprouting is due to: 1) planting too early in cold soils and 2) watering too much early on.
During the growing season.
Water. After the plant is up, dahlias enjoy moist soil. Water deeply multiple times per week, particularly during the hot times of summer.
Fertilizer. A well balanced fertilizer is best. Avoid high nitrogen fertilizer as this will promote excessive foliage growth, increased pest issues, and tubers that don’t store well over winter.
Stopping/Topping. When your dahlias reach 12” tall, pinch off the center shoot to promote bushier plants with more lateral branches.
Disbudding. To promote the largest flowers, remove the first and second pairs of side buds below a main flower bud. The plant will direct more energy into the main growing bud.
Cut Flowers. The best time to cut flowers is during the cool morning. Place the bottom of the stems in very hot water (160 degrees, not boiling) and leave until cool. This will help seal the stems and your flowers will last 4-5 days.
Keep your plants dead-headed to promote continued flowering. Dahlias respond well to cutting; the more flowers you cut, the more the plant will produce.
Insects and pests.
The most common problems with dahlias in our region are spider mites, thrips, aphids and earwigs. Slugs can also eat young tender plants.
Promoting good growing conditions and healthy plants is the best defense.
For a good offense, do an internet search for control of specific insects.
Digging and storing tubers.
October generally marks the end of the growing season in the Okanogan and dahlia foliage will die back after the first frost. If left in the ground, the tubers will freeze over the winter and die. To store your tubers for next year, cut the stock a few inches above the soil line and dig up the clump. Take care to not damage the tubers. Wash the dirt off the tuber clump with a hose and let dry in a location protected from frost. At this point you can either divide the tuber clump in the fall or wait until spring.
Divide tubers with a sharp knife so that each tuber has at least one ‘eye’ on the stem. There are nearly as many methods of saving dahlia tubers over the winter as there are dahlia growers. The most popular are tubers stored in cardboard boxes or plastic bags and then covered in vermiculite, peat moss or wood shavings. The ‘saran wrap’ method also works well. Whichever you choose, store them in a dark, cool location ~38-50 degrees; a well house, root cellar or cool basement all work fine. Protect from freezing and check in on them a couple times during the winter.
Northwind Dahlias 