But which ones to choose and how should you care for them?
Now is the perfect time to order dahlia tubers, because they’re listed from January onwards. If you delay, the best varieties inevitably get snapped up, as I know to my cost! This year supplies are more limited than usual, because the Dutch harvest suffered from a wet summer, just as we did. Most dahlia tubers are commercially grown in the Netherlands and large growers supply many different bulb companies. The likelihood is you’ll be getting the same thing from the same grower, but not necessarily at the same price. So shop around to find the best deal.
What to do when tubers arrive
Once tubers arrive, store them somewhere cool and frost-free. If you have a heated greenhouse, it’s possible to pot them up in the next month, but the tubers won’t put on much growth until the weather heats up. Don’t force them by over-heating your greenhouse, because the plants will just get leggy and spindly. If you have an unheated greenhouse or conservatory, it’s best to wait until late April before potting tubers up.
Select pots that just about accommodate one tuber, because tuber mass varies from variety to variety. Some make very small tubers; others are large and knobbly. Once the dahlias begin to shoot, be prepared to cover them on cool nights – bubble wrap is excellent. Feeding isn’t necessary at this stage. Once your dahlias show flower buds, you can apply a high-potash food such as Vitax Q4. Don’t use quick-release, nitrogen-rich feeds as they promote leafy growth at the expense of flowers.
You can take cuttings from the new growth, but always leave some stem above the tuber so it can reshoot again. Cuttings root easily in gritty compost. Many gardeners pinch back the growth tips on their potted dahlias to make their plants bushier once they reach about 30cm in height. I begin to harden dahlias off in the second half of May by placing them outside during the day. I grow 100 on my allotment and I only move them back if a frost threatens, but outdoor days toughen up the stems and leaves. Keep an eye out for slugs in the evening – dark-leafed dahlias are especially popular with gastropods!
Do I leave them in the ground?
I’m often asked whether it’s a good idea to leave dahlias in over winter. I’m not in favour of it for three reasons. Dahlias emerge later than most perennials, often not reshooting until the middle of June. Their late arrival leaves an enormous gap in the flower border and, by the time the dahlias come through, most perennial plants are way ahead. Dahlias don’t enjoy pushing up through taller plants. Left in, dahlias make large tuber masses over time but bear fewer flowers, so they’ll need dividing anyway. The third reason is that a really cold winter can see them off.
How to grow them in a border successfully
The method used at Great Dixter really works. They leave gaps in the borders and fill them with spring bedding such as wallflowers, tulips and spring bulbs in autumn. These come out at the end of May, then the dahlias go in. You can also make a cutting garden. I dedicate several beds on my allotment to dahlias, but they also contain gladioli, cosmos, mallows and Verbena bonariensis. Their upright presence saves me having to use stakes.
PHOTOS: GAP, SHUTTERSTOCK