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Perennials

Dahlias: Lift ‘Em or Leave ‘Em?

To lift or not to lift, that is the question! Dahlia growers have been divided on this for some 200 years. Are there reasons why it is advisable to lift dahlia tubers, or are we just making a lot of extra work each fall?

Many gardeners, myself included, opt to leave dahlia tubers undisturbed for years. In my case it comes down to time, space to store, and “what would I do with that many tubers if I divided them?” Here in the Puget Sound region, gardeners with good drainage are lucky enough to be able to leave them in the ground if we choose to. Tubers left in the ground usually bloom about 2-3 weeks earlier than tubers lifted and replanted. Eventually dahlia clumps will grow overcrowded and will need to be lifted to be divided.

Gardeners in cold winter areas (or who have soggy soil in winter) don’t have the luxury of choice. These gardeners must lift and store their tubers. Also, if you’re a serious dahlia grower who wants exhibition-quality blooms to show at garden clubs or fairs, it’s a different story. If you have those ambitions, I think starting with new rooted cuttings or tubers each spring gives you the very best chances of raising exceptional flowers.

The best time to lift your tubers is in late October or shortly after we have the first hard foliage-killing frost. Frost or not, lifting tubers is okay by late October. If frost blackens the foliage, it is important to lift your tubers reasonably quickly; once the protective foliage is gone, it is easier to get damage on the tubers. On the other hand, lifting your tubers too early (say early October) may result in immature tubers that have a tendency to shrivel and dehydrate.

Lift or leave, your dahlias will start flowering mid to late July and continue through late October or frost. Dahlias are truly the only bulb or tuber I can think of that gives you such a plentiful array of rainbow colored flowers for so long. Enjoy!

Here are some tips on fall dahlia care.

1. Around late October, remove the remaining flowers.
2. Cut back all stems to 8-10 inches.
3. If you’re lifting them, dig them up with a spade or digging fork, being careful not to injure them.
4. Label each clump with a tie on label, or mark each tuber with a Sharpie.
5. Let the dug tubers dry in a well ventilated area out of direct sunlight. Putting them on open weave plastic flats allows good air circulation.
6. Remove dry soil from tubers.
7. Take a box, line the bottom with a plastic bag, and put a 1” – 1 1/2” layer of peat moss, vermiculite, or dry compost over the plastic. Arrange the tubers so they don’t touch and cover them with an additional 1” – 1 ½” layer.
8. Store through the winter at about 40º F. Keep dry. Check periodically for softness or mold; remove any bad tubers.
9. Replant your lifted tubers in mid April to mid May for best results.
10. If you choose to leave the tubers in place, don’t let the hollow stem ends fill up with water; the water can freeze and ruin your tubers.
11. If you leave the tubers, be sure to protect them from slugs (Sluggo and Worry Free are good products) and wireworms (Bayer Complete Insect Killer).

By Ken Plante
Skylights Autumn 2006 Vol 21, No. 3

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