Finally, the warm days have brought the tubers to life. My divisions (tubers) along with the few that I was able to buy from dahlia specialists are now in trays with potting soil and some vermiculite. Pot clumps from the commercial sellers like Brecks are somewhat behind. If yours are like mine, have patience. Put them in pots or trays with packaged potting soil, sprinkle them a bit and leave them in a warm place.
If you care about names, buy or make some wired plant tags and keep them with the tubers or clumps. Label with widely available Sharpie markers - choose permanent and industrial. Or for labels that will last for years, opt for a label maker with outdoor, thermal tape.
The soil in our garden is dry. There has been very little rain in the past month. This is a good time to put stakes into the ground. In most areas dahlias will grow to 4-5 feet tall, so they will need a metal, plastic, or wooden stake to keep them stable. Small container dahlias can be planted into pots, 10 inches or bigger, or directly into the ground.
Dahlias can be planted in any garden bed where you can grow tomatoes. At the start, the dahlia plant will be fed from the tuber. Later it will put out roots. Rarely, a plant will not make roots and it will stop growing when nutrient from the tuber is exhausted. If that happens gently dig out the tuber and check for roots. Dahlias grow roots near the ground. A handful of time-release or general fertilizer, scratched into the surface will be sufficient. Do not put the fertilizer under the tuber. It will do more harm than good.
Plant the dahlia about two or three inches below the soil surface with the eye or shoot facing up. Do not make it struggle to find light. If the shoot has leaves, do not bury them. You can always fill in later as the plant grows. Remember the tag.
On the first weekend in May our local farmers market had stands filled with blooming container dahlias. Many were doubles with closed centers, and one had a red and white cactus form plant. Container-size dahlias are short, have a long blooming period and grow well on terraces, balconies, or in the front of the garden. An ADS article on growing container dahlias is available below. The techniques, including the removal of spent blooms, are typical of those for other outdoor plants. If you dig the clump out after a frost, they will overwinter like the taller cousins.
Current weather forecasts illustrate the variability of Spring weather conditions across the country. Here in Northern Virginia, we can start planting without much risk of frost. Even if Jack Frost makes one last appearance, new shoots will sprout from the tuber. If you have rooted cuttings, let them grow indoors for a few more weeks.
Many instructions recommend planting the tuber four to six inches deep with fertilizer under the tuber. That will make the shoot struggle to break ground, particularly if there is a lot of clay. A better approach is to lay the tuber flat with the base of the shoot two to three inches below the surface. If the tuber has leaves, don’t bury them. Leave a saucer shape around the plant and fill it in as the plant grows. Dahlias are surface feeders, and their roots will grow an inch or two below ground level. Sprinkle the fertilizer around the plants, but not against them. Fertilizer spread under the tuber may do damage to the tuber which will feed the plants before the roots develop.
Make sure you put a stake in at planting time, so you won’t impale the tuber later in the season. If you care about plant names attach a tag to the stake and make a chart in case the tag is lost.