Dahlias and gladioli bloom magnificently until the first frost, but then it is over: their tubers come from warmer regions and freeze in our ground. Whoever wants to keep them must dig them up and store them frost-free over winter. Done right, the same tubers sprout again every year and even grow larger over time.
Four steps lead safely through winter: dig up, dry, store and divide in spring. This article shows you each of them, so your dahlias last many years.
Digging up after the first frost
Wait with digging up until the first frost has blackened the foliage, usually between weeks 42 and 46. Until then the plants still draw energy into the tuber store, which strengthens them for the next year. Cut the frosted foliage back to a hand's width.
Then lift the tubers carefully with a digging fork, in a wide arc around the plant so you do not pierce them. Shake off coarse soil, but do not wash the tubers, that promotes rot. Treat gladiolus corms the same way.
Drying and storing
Let the dug-up tubers dry off for a few days in an airy, frost-free place, best upside down so residual moisture drains from the stems. Only once the surface has dried do they go into winter storage.
Store the tubers cool, dark and frost-free at about five to ten degrees, for instance in the cellar. Bed them loosely in dry sand, coir or newspaper so they do not touch. That way they stay plump without rotting. Check them a few times over winter and sort out soft or mouldy pieces.
Cut back the foliage
Wait for the first frost and cut the blackened foliage back to a hand's width above the ground. With several varieties, mark the name on the stub.
Lift carefully
Push the digging fork in a wide arc around the plant and lift the whole clump out. Do not pull on the stem, or it tears from the tuber.
Clean and let dry
Shake off coarse soil without washing. Let the tubers dry for a few days upside down in an airy, frost-free place.
Store frost-free
Bed the dry tubers in sand or paper and store them cool, dark and frost-free. An unheated cellar or a frost-free garage is ideal.
Check over winter
Look in a few times. Cut away rotten spots generously, lightly moisten shrivelled tubers. That way they reach spring healthy.
Dig up after the first frost, dry well, store cool and dry. Whoever lifts and divides the tubers yearly makes a whole bed from one dahlia over the years.
The core rule for overwintering
Frequently asked questions
Do you have to dig up dahlias every year?
In most regions yes, because dahlia tubers are not hardy and freeze in the ground. Only in very mild wine-growing areas do they sometimes overwinter outside with a thick mulch layer. Safe is digging up and frost-free storage.
When do I dig up dahlias and gladioli?
When the first frost has blackened the foliage, usually weeks 42 to 46. Until then the plant still draws nutrients into the tuber. Afterwards cut the foliage back and lift the tubers carefully.
How do I store dahlia tubers correctly?
Cool, dark and frost-free at about five to ten degrees, for instance in the cellar. Bed the dried tubers loosely in dry sand, coir or paper so they do not touch, and check occasionally over winter.
Why do my stored tubers rot?
Usually because they were stored too moist or the store is too warm. Let the tubers dry well before storing, do not wash them and provide a cool, airy store. Cut away rotten spots at once.
How do I divide a dahlia tuber?
Best in spring when the eyes are visible. Split the clump with a clean knife so that each piece carries a section of crown with at least one eye. Pieces without an eye do not sprout and go on the compost.
