Lift dahlias, cannas and gladiolus once a frost has blackened the foliage, and no later than a week or two after it. At the Newark weather station, the first 32°F freeze arrives between November 4 and November 16 (NOAA NCEI U.S. Climate Normals 1991-2020). That puts digging at roughly the second week of November through the end of the month. Suburban and hill-country gardens freeze one to two weeks sooner, and their digging moves earlier by the same amount.
Do you have to dig them up in New Jersey?
Yes. The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places New Jersey between zones 6a and 7b. No part of that range is mild enough to leave all three plants in the ground the way you would a daylily. Plan to dig dahlias, cannas and gladiolus every fall.
The USDA system rests on a single variable, the average annual extreme minimum temperature. It tells you how cold the worst night of a typical winter gets, and it is a useful sorting tool. A second number shows what a normal winter feels like. At Newark, the mean daily minimum of the coldest month is 25.5°F (NOAA NCEI Climate Normals 1991-2020). That is an average, so an ordinary January includes plenty of nights colder than that. The soil does not stay frozen all winter, but it freezes and thaws repeatedly, and it freezes deepest in the northern counties and on higher ground.
Dahlia tubers, canna rhizomes and gladiolus corms are all swollen storage organs full of water. When that water freezes, ice crystals rupture the cells, and the tissue turns to mush as soon as it thaws. Cold, waterlogged soil does similar damage even without a hard freeze, especially in heavy clay, which holds water around the roots through a wet New Jersey winter.
The three do not share the same risk. Cannas are the most forgiving. In the warmest, most sheltered pockets, such as a city garden against a south-facing wall or a spot near the shore, a canna under a thick layer of mulch sometimes comes back. That is a gamble you can afford to lose only if the plant is cheap and easily replaced. Dahlias and gladiolus corms are less tolerant of frozen ground, and the northern counties and the hills, with an earlier first frost and colder soil, are where lifting is not optional for any of the three.
Hardy spring bulbs follow different rules. Tulips, daffodils and crocus need winter cold and are meant to stay put. Which Spring Bulbs Survive Your Winter sorts out which bulbs belong in the ground all year and which belong in a box.
When to lift them
The signal is a frost that blackens the foliage. A light touch of frost that nips a few leaf edges is a warning, not the cue. Once the leaves turn dark and limp, the plant has stopped feeding the underground parts, and the tubers, rhizomes and corms are finishing their growth. Lift them within about a week or two after that blackening frost.
What is the lifting window in New Jersey?
Counting from the first fall freeze at Newark, November 4 to November 16, the window runs from about the second week of November to the end of the month. That reference figure comes from an airport station, though, and most gardens differ from it. Suburban and rural sites typically see the first fall frost one to two weeks earlier, and more at elevation. For those gardens, the lifting window opens in the final days of October or the first days of November and runs into mid-November.
The colder the spot, the earlier the work. A garden in the northern hills will freeze before one in the Newark area, so the shovel comes out sooner there. Your own county’s first-frost range is the number to plan around, and the First and Last Frost Dates in New Jersey page gives a place to check it. Your county extension office can tell you how local frost compares with the airport reading.
Why not lift them earlier?
Lifting early feels like the safe move, because it beats the cold. It backfires. While the foliage is still green, the plant is pulling sugars down into the tubers and thickening their skins. Tubers dug during that period are immature. Their skins are thin and scuff easily, and their flesh holds more water than it should. They cure poorly, and a month later they are soft in the box.
Cutting a green stem also leaves a fresh wound at the crown, where rot gets in. Waiting for the frost lets the top die back by itself, and the tubers then sit in cool soil for a few days to a week or two while the skins firm up.
Waiting too long is the opposite mistake. Once the ground begins to freeze solid, tubers start to be damaged, and a wet spell can rot them while you wait. If frost is forecast and the foliage is still green, cover the plants overnight with a sheet or row cover. Because the first frost usually comes well before the first deep freeze, that buys you time to let the foliage finish dying back before you dig.
How do you lift each one?
Cut dahlia and canna stems back to a short stub. Push the fork in well out from the stem and lever the clump up gently, since tubers snap at the neck and a broken neck rarely heals. Lift gladiolus by loosening the soil around the plant and pulling the whole plant out with the corm attached. Shake off the loose soil and move everything somewhere sheltered from rain and frost. Do not leave anything in the sun or in a pile where it can heat up.
Storing them over winter
Cure first, clean lightly, then store the bulbs cool, dark and slightly moist, so they neither rot nor shrivel. The three plants do not want exactly the same conditions, and the differences are why a single storage method fails with one of them.
How do you cure and clean them?
Curing means letting the surface dry in a sheltered, airy place that stays above freezing, such as a garage corner or a covered porch. Dahlia tubers are ready when the skin feels dry and set, and canna rhizomes follow the same cue. Gladiolus corms take longer. They are ready when the husks are papery and the old corm pulls away easily from the new one. Brush off soil with your hands, and skip the hose, because a wet tuber is where rot starts. Trim any broken or mushy parts and label each clump. Dahlia varieties are easy to mix up by spring.
How do dahlias, cannas and gladiolus differ in storage?
| Plant | What you store | Packing | Moisture |
|---|---|---|---|
| Dahlia | Tuber clump | Box or crate with a loose, barely damp medium such as wood shavings or peat | Slightly moist; tubers shrivel fast if dry |
| Canna | Rhizome clump | Similar packing, with a little more air around it | Barely damp; too wet and the rhizomes rot |
| Gladiolus | Corm, old base removed | Mesh bag or paper bag, hung or in a shallow tray | Dry and airy; moisture invites mold |
Dahlias are the most prone to drying out, because their thin skins lose water readily. Cannas sit in the middle, and the rhizomes are tougher. Gladiolus corms are a different kind of storage organ, closer to a dry onion. They keep best in open, dry air, away from damp packing.
For all three, the spot should be cool, dark and above freezing. A basement or an interior closet works well. An unheated garage is riskier than it looks. With the Newark coldest-month minimum at 25.5°F, a detached or poorly insulated garage can freeze in a normal January and destroy everything in the box.
How often should you check them?
Check the stored bulbs regularly from late fall until spring. It is the habit that saves the most of them. Look through each box. A tuber that has gone wrinkled and light needs a small mist of water on the packing. A soft, dark or moldy spot should be cut away with a clean knife, and the cut surface left to dry before the piece goes back in. If a box smells musty, replace the medium with something drier. Gladiolus corms that feel soft or show gray mold should be pulled out before they spread it.
What goes wrong
Most losses come from four problems, and each one leaves a clear sign.
- Rot. The tuber feels soft, smells sour and may show gray or white mold. It comes from storing them wet, packing them before they have cured, or leaving broken skin untrimmed. Cure thoroughly, keep the medium barely damp, and give each box some air.
- Shriveling. Tubers turn wrinkled, light and leathery, and eventually will not sprout. The storage spot is too dry or too warm. A light mist on the packing during the monthly check fixes it early. A shriveled tuber that is still firm inside can usually be saved.
- Lifting too early. Tubers dug while the foliage is still green have thin skins, and they decay in storage even when everything else is done right. Wait for the frost to blacken the leaves, then lift within about a week or two.
- Leaving them in the ground too far north. The colder parts of New Jersey, meaning the northern counties and higher ground, have an earlier first frost and colder soil than Newark. Heavy mulch there does not make up for it, and the clumps are usually soft by spring. Even in a milder garden, wet clay is a hazard on its own.
One cheap safeguard is to mark each clump before it goes into storage, especially when you lift several dahlia varieties. Once the tubers lose their tops, they all look alike, and a mix-up only shows when the blooms open in summer.
Common questions
Can I leave dahlias in the ground in New Jersey if I mulch them heavily?
It can work in the mildest, best-drained gardens, but it is a risk. Winters here freeze and thaw the ground repeatedly, and wet soil rots tubers as readily as cold does. In the northern counties and on higher ground, with earlier frost and colder soil, it fails often enough that lifting is the sensible default. If you want to experiment, leave a single clump in the ground and store the rest.
Do I wash the tubers before storing them?
Brush off loose soil, but do not rinse them. Surface water slows curing, and wet tubers are the ones that rot first. If a clump is caked with heavy clay, let it dry and then knock the soil away. Dahlia and canna clumps can keep some clinging soil without harm. It helps hold a little moisture.
When do I plant them back out?
Plant after the last spring frost has passed and the ground has warmed. These plants are tender, and a late frost will kill new shoots. The First and Last Frost Dates in New Jersey page can help you find your county’s spring range. Dahlias are best divided in spring, when you can see the growing buds on the crown.
Do tulips and daffodils need lifting too?
No. Tulips, daffodils, crocus and other hardy bulbs stay in the ground and need winter cold to bloom. See Spring Bulbs for the full picture, and Planting Spring Bulbs in New Jersey for timing in the state. More fall jobs are collected in the New Jersey guides. The tender bulbs you lift in November come back out in spring, while the hardy ones are planted in the fall for the following year.