Dig dahlias, cannas and gladiolus in Delaware once a frost has blackened the foliage, within about a week or two. At the Wilmington reference station, the first 32°F freeze arrives between October 26 and November 7, so lifting runs from late October into November. Gladiolus can come up a little sooner, once the leaves yellow. Colder, higher or more rural gardens should expect the whole sequence to start earlier.
Do you have to dig them up in Delaware?
The USDA Plant Hardiness Zone Map 2023 puts Delaware in zones 7a to 8a. That system rests on one number, the average annual extreme minimum temperature, and it says nothing about how wet the soil is or how long a cold snap lasts. Still, the verdict is clear enough: in most of the state, these plants come up each fall. Where the ground stays unfrozen under mulch, they can sometimes stay put. Delaware’s ground does freeze in a normal winter.
NOAA’s 1991-2020 Climate Normals for Wilmington give a mean daily minimum of 25.6°F in the coldest month. That is an average, so individual nights run lower, and the top few inches of soil, where dahlia tubers, canna rhizomes and gladiolus corms sit, cool right along with the air. All three are fleshy storage organs full of water. When that water freezes, ice crystals rupture the cells, and the thaw leaves mush. Nothing about it looks wrong until spring, when nothing comes up.
The colder end of the 7a to 8a range lies up north and inland, and the milder end toward the southern and coastal parts of the state. That is where the line falls. In the northern reaches, lifting is not a debate. In the milder southern and coastal pockets, some gardeners get cannas through under a thick mulch in an easy winter, and a few get dahlias through in a sheltered, well-drained bed. It is a bet, not a method. A single hard January can erase a collection built over years.
A practical compromise for anyone tempted to test their luck: lift most of each variety and leave one clump behind under mulch as an experiment. If it sprouts in spring, you have learned something about your own yard. If it does not, you lost one clump instead of the whole planting. Plan to lift all three every fall in Delaware and treat anything that survives in the ground as a bonus.
Tulips and daffodils are a different story, since they are built for cold ground. Which Spring Bulbs Survive Your Winter covers that side of the bulb world.
When to lift them
Wait for the frost to do the signaling
The cue is a frost that blackens the foliage. Dahlia leaves and canna leaves go limp and dark, and the plant stops feeding the underground parts. NOAA’s 1991-2020 normals for the Wilmington airport station (USW00013781) place the first 32°F freeze between October 26 and November 7, a band that covers the 30 to 70 percent probability range. Lift within about a week or two after the first frost blackens the tops, which at the reference station means late October into November.
That band comes from an airport weather station, and gardens do not behave like airports. Suburban and rural plots often see the first fall frost one to two weeks earlier, and more at elevation. So a garden in the higher, colder northern part of the state will usually be lifting earlier than a garden near the coast. Check your own county rather than treating the Wilmington range as a statewide promise. The First and Last Frost Dates in Delaware page is a useful place to compare, and the wider Delaware guides cover the rest of the seasonal calendar.
Once the tops are black, cut the stalks down to a few inches, loosen the soil in a wide circle with a garden fork, and lift from the outside in. Prying at the stem is how dahlia necks snap, and a tuber without a neck will not sprout.
Why lifting early backfires
Pulling tubers in September because the beds look ragged feels tidy. It is also how storage rooms fill with rot. Until frost shuts the plant down, the foliage is still moving sugars and starches into the roots, and the skins are still thin. Tubers lifted at that stage are immature: they hold extra water, they do not cure properly, and they either shrivel or go soft within weeks. A tuber that has finished its season, by contrast, has a firmer skin and holds up in a box for months.
Waiting has limits, though. A week or two is the window, not the whole of November. Leaving them through repeated hard freezes lets cold reach the crown, and sodden fall soil adds its own rot risk.
Gladiolus run on their own clock
Gladiolus corms do not need the frost signal in the same way. Lift them when the leaves yellow and brown, which for many plantings arrives before dahlias are finished. Late-planted ones may still be green when the first frost comes. Either way, dig them before the soil turns cold and heavy. Once the beds are empty, fall is also the moment to plant the hardy kinds, as laid out in Planting Spring Bulbs in Delaware.
Storing them over winter
Cure first, clean lightly
Fresh from the ground, all three need to dry before they go into a box. Set them somewhere sheltered, airy and out of the rain, such as a garage bench, a covered porch or a shed, until the surface skin feels dry to the touch. For dahlias and cannas, that usually takes a few days. Brush off loose soil with your hands or a soft brush. Washing is a matter of taste: a gentle rinse followed by thorough drying shows you what you have, but a clump left with a little soil clinging to it stores just as well. What matters is that no wet mud goes into the box.
Dahlia stems are hollow, and water that sits in the cut stalk runs straight into the crown. Turning clumps upside down for a short stretch lets it drain before packing.
The three do not want the same thing
Cool, dark and slightly moist is the right target for dahlias and cannas. Gladiolus corms break the pattern: they want to stay dry.
| Plant | After lifting | Packing | Moisture |
|---|---|---|---|
| Dahlias | Dry the surface, leave clumps whole or divide later | Cardboard box or ventilated crate with wood shavings, peat or vermiculite | Slightly moist, never wet |
| Cannas | Cut stems back, dry briefly, leave a little soil on | Crate or box with barely damp peat or shavings | Slightly moist; rhizomes shrivel fast if dry |
| Gladiolus | Cure in a warm, airy spot, remove the old shriveled corm | Paper or mesh bags with air movement | Dry |
Whatever the plant, the place has to stay above freezing and out of the light. An unheated basement, a closet against an interior wall or an insulated corner of a garage can all work. Given that the average low in Wilmington’s coldest month is 25.6°F, a detached shed or an exposed garage wall can drop below freezing on the worst nights. Pick the spot with that in mind.
The monthly check
Storage is not set-and-forget. Open every box once a month through the winter and look at each piece. A tuber that has turned soft or smells sour should come out immediately, along with any packing material it touched. A wrinkled one is telling you the air is too dry: a light mist on the packing, not on the tuber itself, usually fixes it. Gladiolus bags that feel damp need a day out in open air. Ten minutes a month is the difference between a collection that comes through and one that is lost by March.
What goes wrong
Rot is the most common loss. Tubers turn soft, brown or gray at the neck or the tip, and a sour smell or fuzzy mold follows. The cause is too much moisture, poor airflow or storing before the surface dried. Prevent it by curing first, using only barely damp packing and sorting out bad pieces at every monthly check. Cut away small soft spots on a dahlia or canna with a clean knife and let the cut dry before returning it to the box.
Shriveling is rot’s opposite. The tuber wrinkles like a raisin and goes light in the hand. Usually the room is too warm or too dry, or the packing dried out completely. A little moisture in the packing and a cooler spot slow it down. Wrinkled gladiolus corms are the exception: those are fine dry, and the thing to check is firmness, not wrinkles.
Lifting too early produces both problems at once, because immature tubers have thin skin and extra water. The first sign is often a cluster of soft, discolored tubers by midwinter. The fix comes the next fall: wait for the blackened foliage.
The last mistake is geographic. Advice written for the Deep South, or for the coast of the Carolinas, often says to leave cannas and even dahlias in the ground under mulch. In Delaware, with a coldest-month average low of 25.6°F in Wilmington and colder winters farther north and inland, that advice borrows a milder region’s margin. When in doubt, lift, and keep any in-ground experiment small.
Common questions
Can I leave cannas in the ground in Delaware?
Sometimes, in the milder southern and coastal parts of the state, under a thick layer of mulch in a well-drained bed. Colder, wetter or more inland gardens should lift them. If you try it, keep a few rhizomes in storage as insurance.
What if the first frost is only light?
Wait. A frost that nips a few leaves while others stay green has not shut the plant down. The signal is foliage that has been blackened, and the first 32°F freeze at the Wilmington reference station falls between October 26 and November 7, so a light nip can come first in colder gardens.
Do gladiolus need to be dug every year in Delaware?
Generally yes. Gladiolus corms are tender, and a few survive mild winters in sheltered spots, but plantings left in the ground tend to decline. Lifting also lets you remove the old spent corm and separate the small cormels.
Where should I keep the boxes?
Choose a cool, dark place that stays above freezing. An unheated garage or shed can dip below freezing during cold snaps, since the average low in the coldest month at Wilmington is 25.6°F. A basement or an interior closet is the safer bet, and a thermometer left in the spot costs very little.