Dahlia planting
I started planting my dahlias this week now that the calendar has turned to June. The hot weather in the past few days has warmed the soil and we seem to be past the risk of frost (knock on wood!). It is really important to wait until the soil is warm when planting dahlias as cool or cold soil will delay growth and can increase the risk of your tubers rotting. Once conditions are favourable, dahlias grow like a weed! Here is a look at our dahlia planting and growing procedures.
I usually plant my dahlias in a bed that has been used for spring bulbs like tulips. As we rip out the spent tulip bulbs, we weed thoroughly, then amend the bed with fresh compost, granular organic fertilizer and alfalfa pellets for a quick nitrogen boost. The bed is raked smooth and then ready for tubers.
I plant my tubers in a spot that receives full sun. I dig a wide but shallow hole, about 2-3” deep. I place my tuber in the hole with the sprouted eye facing up and the tuber lying on its side. Dahlias also do really well in pots.
I space my dahlias 12” apart but for home gardeners 18” to 24” is ideal.
Dahlias need support. Their hollow stems snap easily in windstorms or even just from the weight of the flowers once they start blooming. We use rebar with baler twine to construct support around our plants but tomato cages also work well. Some larger varieties like dinner plate dahlias will be too big for a tomato cage and will need sturdy stakes with twine to keep their stems from snapping.
If your dahlias have just barely sprouted when you plant them, don’t water too heavily. Once you see lots of green leafy growth, make sure they get watered regularly if there is no rain. We fertilize regularly with liquid fish emulsion and a liquid bloom promoter once we see flower buds forming.
Pests to be aware of: pretty much everything! Thrips, grasshoppers, slugs, caterpillars, you name it, they love dahlias! I keep the soil under my dahlias clean of weeds and mulch to discourage slugs. As for grasshoppers, they love to eat the dahlia buds and flowers. When there is heavy grasshopper pressure, we bag all our buds with organza bags to ensure perfect blooms. Fortunately dahlias are very productive so even if a few blooms get munched on, there are more that are untouched. The same bagging technique protects against thrips and caterpillars. I do not spray with any pesticides and am able to produce lots of beautiful blooms with the organza barriers and ensuring our soils are healthy.
As your dahlia grows, you may want to pinch out the central stems once it reaches about 12-18” tall. This will encourage a bushier plant. I confess I do not do this as it delays the first blooms by 2 weeks or so. Instead, I cut that first central bloom quite deeply and it does the same thing, encourage side shoots. In our short growing season, I am reluctant to delay blooming with pinching. Before we had hoophouses for growing dahlias in, 2 or 3 weeks might be my entire outdoor dahlia season. If you have the ability to protect your dahlias from frost, pinching might make sense.
The last thing to do is enjoy the show! Dahlias come into their prime once the nights are cooler but the days are still warm, usually late August or early September. Make sure to cut some of those blooms for yourself to enjoy after all the hard work of pampering these divas of the garden.