How to Overwinter Tender Perennials: Dahlias, Cannas, Elephant Ears
How to overwinter dahlias, cannas, and elephant ears — when to dig, how to cure and store tubers and rhizomes, cold frame options, and how not to lose an expensive collection to winter rot.
When to do this
The signal is the first light frost. A light frost (<28°F for a few hours) kills back the foliage of dahlias, cannas, and elephant ears without damaging the underground storage organs. This dormancy signal is actually useful — plants that have experienced this first frost are better prepared for dormant storage than plants dug before any frost. Per Penn State Extension, "dig dahlia tubers after the first killing frost blackens the foliage" but "before a hard freeze (below 25°F for more than a few hours) damages the tubers." In zone 7a Long Island, this typically means mid-to-late October, though 2023 was notably late — I didn't dig mine until November 3.
Do not wait: frozen tubers are usually unrecoverable. A single hard freeze to the storage organs, not the foliage, ends the collection. Mark your calendar for the first expected frost and be ready.
What you need
- Garden fork for digging (spade damages more tubers) — search "digging fork garden" for options
- Bucket of water and stiff brush for cleaning
- Sharp knife or pruners for dividing
- Sulfur dust or garden lime (for treating cut surfaces)
- Perlite, dry peat moss, or barely moist vermiculite for storage medium
- Ventilated crates, bins, or mesh bags for storage
- Labels — this is critical; all tubers look identical in spring
Dahlias: step-by-step
Step 1: Cut back foliage
After the first frost blackens the foliage, cut plants back to 4–6 inches above ground. This reduces moisture loss and makes digging easier. Leave the stubs — they help you locate the clump.
Step 2: Dig carefully
Insert the garden fork 6–8 inches from the main stem and lever upward. The tuber clump is larger than the plant looks above ground. Work around the clump from multiple sides rather than digging straight in, which breaks necks (the connection between tuber and old stem — each tuber needs a piece of neck with an eye to sprout). A broken neck tuber is not useless, but it won't sprout reliably.
Step 3: Rinse and inspect
Wash the clump with a firm spray of water. Remove soil and damaged or rotten tubers. Per University of Minnesota Extension, "shriveled, mushy, or completely hollow tubers will not survive storage" — cut them away, dust the cut with sulfur, and set aside healthy tubers.
Step 4: Cure (dry down)
Place cleaned clumps upside down (to allow moisture to drain from the hollow stems) in a cool, airy location for 5–7 days. This curing step is important — it toughens the skin and reduces moisture content before storage. Per Penn State Extension, "adequate curing reduces storage rot significantly."
Step 5: Divide if desired (optional)
You can divide the clump now or in spring. Spring division, when eyes are more visible as they swell, is easier and more reliable for identifying viable tubers. For large collections that need the space, fall division with sharp clippers and sulfur-dusted cuts works too. Each division must have: at least one healthy tuber, a piece of neck, and at least one visible eye (small, pointed pink or yellow bump near the neck).
Step 6: Pack for storage
Pack divided or whole clumps in ventilated crates or mesh bags with barely moist perlite, peat, or vermiculite between them. The medium should feel just slightly damp — if you squeeze it and water comes out, it's too wet. Too wet = rot. Too dry = desiccation. Per University of Minnesota Extension, "40–50°F and 40–50% humidity is ideal — a basement, unheated garage, or root cellar" works well. Check monthly and remove any rotted tubers immediately before rot spreads.
Cannas: step-by-step
Canna rhizomes are more forgiving than dahlia tubers. Cut back foliage to 6 inches, dig the rhizome clump with a fork (they're usually shallower than dahlias — 6–8 inches down), rinse, and allow to cure for 3–5 days. Per University of Minnesota Extension, cannas are "one of the easiest tender perennials to overwinter" because their thick rhizomes are less prone to desiccation than dahlia tubers. Store at 45–55°F in barely moist peat or vermiculite, or simply store the entire dry clump in paper bags or mesh bags without medium. Check in January and February for signs of rot.
Elephant ears (Colocasia, Alocasia): step-by-step
Two genera, different storage behavior. Colocasia esculenta (taro): stores similarly to canna — large corns (starchy corms) that prefer somewhat more moisture during storage than dahlias. Store at 50–60°F in slightly moist peat. Per UF IFAS Gardening Solutions, "elephant ear corms should not be stored completely dry — they are prone to desiccation." Alocasia species: more cold-sensitive; bring rhizomes indoors to a warmer storage location (55–65°F) to prevent chilling injury. Some growers overwinter small Alocasia as houseplants — move pots indoors before frost to a bright, indirect-light location and reduce watering to monthly through winter.
Cold frame storage as an alternative
For zone 6–7 gardeners, a cold frame (simple wooden box with a glass or polycarbonate lid) over an in-ground planting of cannas and elephant ears can keep ground temperatures above 28°F through winter in many years without digging. Per Penn State Extension, "cold frames can extend the effective hardiness by approximately one zone." The risk: an unusually cold winter kills the in-ground stock. Keep a separate in-door backup of key varieties when using cold frame overwintering as the primary method.
How this fits my Long Island schedule
Dahlias are the treasure of my zone 7a cutting garden — I grow about 30 varieties on the south side of my property. The first October frost is my trigger. I cut everything back on frost day, then spend the following Saturday digging, rinsing, and labeling. Everything goes into a wire-rack shelving unit in my basement (which stays at 48–52°F through winter). I check monthly, remove the occasional soft tuber, and by late March they're showing eyes and ready to start in containers under grow lights in the garage. The whole system took two seasons to dial in. The key insight was that the storage medium should feel like a wrung-out sponge, not wet earth — wetter than I was doing originally, which had caused desiccation, but much drier than my first instinct.
Common mistakes
Storing in plastic bags sealed airtight: without airflow, condensation builds and rot spreads through the entire collection within weeks. Always store in ventilated containers. Not labeling before storage: all dahlia tubers look identical by March. Invest in waterproof labels written with a Sharpie before you lose track of variety names. Waiting until the foliage fully collapses on its own before digging: by the time foliage dies naturally in zone 6–7, hard frosts have usually already occurred, risking frozen tubers.