Every autumn, thousands of perfectly healthy dahlias, geraniums and begonias go on the compost heap — not because they died, but because nobody told their owners they don't have to. Tender plants aren't annuals. Given a frost-free winter, most will come back next year bigger, earlier and completely free.
Overwintering is less work than it sounds: an afternoon of lifting and potting in October, a monthly check through winter, and a head start next May that no seed packet can match. This guide covers which plants are worth saving, the three methods that work, and the step-by-step for dahlias — the plant most people lose first.
- Act by the first proper frost — mid to late October in most areas
- Storage temp 5–10 °C, frost-free and airy: shed, garage, cool spare room
- Light dormant tubers need none; plants kept in leaf need a bright sill
- Check monthly — rot gets cut out, shrivelled tubers get a mist of water
Tender or hardy? Know what you're saving
Hardy plants — most perennials, spring bulbs, the hardy annuals you sow in autumn — shrug off frost and need nothing from you. Tender plants come from climates without winter: dahlias from Mexico, pelargoniums from South Africa, begonias from the tropics. One night below zero turns their cells to mush.
The tender list worth saving: dahlias, pelargoniums (bedding "geraniums"), tuberous begonias, fuchsias, cannas, osteospermums and salvias like 'Amistad'. True annuals — cosmos, sunflowers, zinnias — cannot be overwintered no matter what you do; they flower, set seed and finish. For those, the trick is collecting their seed instead and sowing fresh next spring.
Three ways to overwinter — pick per plant
There is no single method; there are three, and the right one depends on what the plant keeps underground.
Lift & store dormant
Dahlias, tuberous begonias, cannas — anything with a tuber or rhizome.
- Lift after frost blackens the foliage, dry, box in barely-damp compost
- Dark, frost-free, 5–10 °C — no light or watering needed
- Takes the least space: a stack of boxes in the shed
Keep in growth (or as cuttings)
Pelargoniums, fuchsias, salvias — plants with no storage organ.
- Pot up, cut back by half, keep on a bright frost-free windowsill
- Water sparingly — once a fortnight is usually plenty
- Take a few cuttings in September as free insurance
The third method is the lazy one: in mild gardens and free-draining soil, dahlias can stay in the ground under a thick 15 cm duvet of mulch. It works until the winter it doesn't — one wet freeze and they're gone. If your soil sits wet, lift.
Lifting and storing dahlias, step by step
Dahlias are the test case: get these right and everything else is easier. Wait for the first frost to blacken the foliage — it signals the tuber to go dormant.
- Cut down the blackened stems Leave 10–15 cm of stem as a handle. Label it now — every dahlia tuber looks identical by February.
- Lift with a fork, not a spade Start 30 cm out from the stem and lever gently. Tubers snap easily, and a snapped neck cannot regrow.
- Dry upside down for two weeks Shake off the soil and stand the clump stem-down somewhere airy so moisture drains from the hollow stems.
- Box in barely-damp compost or sand Tubers touching neither each other nor the box sides, crowns just proud of the surface, in the frost-free spot you chose.
- Check monthly, replant in May Cut out any soft rot; mist shrivelled tubers lightly. Pot up in April for an early start, plant out after the last frost.
Common mistakes
- Waiting for a "proper" frost forecast. The first frost often arrives unannounced. Have boxes and compost ready from early October.
- Storing tubers wet. Skipping the two-week drying stage is the number one cause of rotted boxes in January.
- A heated living room. At 20 °C plants either break dormancy or dry to a crisp. Cool is the whole point: 5–10 °C.
- Watering dormant plants on schedule. A dormant pelargonium needs a mean sip a fortnight at most; kindness kills more than frost does.
- No labels. Come spring you'll want the dark reds at the back of the border — not a lucky dip.
Frequently asked questions
Can I leave dahlias in the ground over winter?
In mild areas with free-draining soil, yes — cut down after frost and cover with 15 cm of mulch. On clay or in cold gardens the risk of a wet freeze is too high; lifting is the only reliable method.
Do overwintering geraniums need light?
Yes — unlike dormant tubers, pelargoniums keep their leaves and need a bright, cool windowsill. If you have no space, take cuttings instead: ten young plants fit on the sill one parent plant occupies.
When can tender plants go back outside?
After your last frost — mid May for most of Britain and the Netherlands. Reintroduce them gradually over a week or two, exactly as you would harden off seedlings.
Is overwintering worth it, or should I just buy new plants?
A stored dahlia starts the season as a multi-stemmed clump that flowers weeks earlier than any new purchase. That said, dahlias, geraniums and begonias also grow surprisingly easily from a spring sowing — seed is the cheapest insurance policy there is.
An afternoon's work in October buys you a border that's a month ahead next June — and plants that get better every year. For the gaps that winter leaves anyway, browse our geranium, begonia and full flower seed collections, or dig deeper in the growing guides library.
