If you stored dahlia tubers over the winter, by now you should have removed them from storage and checked their viability. Each tuber must have an eye or it will not grow. Most dahlia suppliers have stopped sales on-line by now, but you can check dahliaaddict.com to see what’s available. If you haven’t purchased varieties you want for this season, local dahlia societies will be selling tubers soon. [Rhode Island Dahlia Society’s annual tuber sale will be held May 5th at 1:00 p.m. at the North Kingstown Community Center in Wickford.]
Bring your tubers into a warm area. This will help them to “eye-up”; that is, begin showing the eyes (the growth points). If you prefer to start your dahlias indoors rather than planting directly into the ground, use any good potting mix as a planting medium. (I like general purpose ProMix with mycorrhizae.) The mix should be slightly damp, not wet, because dahlias can rot or develop poorly if the soil is too wet at planting.
Start your dahlias about six weeks before you plan to plant them outside. Plant each tuber horizontally (or at a slight angle if the pot isn’t large enough) 2 to 3 inches deep. Keep your pot in a warm place (60 degrees or more). Many varieties will poke through the surface after a week or two. Once the plants have sprouted, water them regularly. They should be grown under lights kept four to six inches above the plants to keep them from becoming spindly.
The next step is to prepare your garden. If you are growing dahlias for the first time, you will need to select a site for your dahlia bed. Dahlias need six to seven hours of direct sunlight daily for optimum growth but will do reasonably well with four hours of sunlight a day (although they will bloom later). The richer the soil is in organic material, the better the blooms will be from your plants. Make sure the area you select drains well. Dahlias require a lot of water while growing but the tubers do not like to sit in water. So, good drainage is essential. A soil test at this time would be valuable if you haven’t done one for a while. Soil that is too acidic or too alkaline will hinder the plant’s ability to absorb the nutrients it needs. Soil pH of 6.5 will ensure that your dahlias will efficiently absorb the necessary nutrients from the soil.
Stop by next month for a few tips on what to do in May!