October arrives, the first frost forecast appears, and your garden is full of plants that have never met a British winter: the dahlias still flowering, the olive in its pot, the banana you bought on holiday optimism. Tender plants — those that cannot survive frost — need a winter plan, and “hope for a mild one” is not a plan. Every year, thousands of pounds’ worth of beloved plants die in the first cold snap for want of an afternoon’s preparation.
This guide explains how to overwinter tender plants safely: which plants need help, the three main strategies, timing, and the mistakes that kill more plants than frost itself.
Which Plants Are Tender? (Know Your Enemy: Frost)
“Tender” means damaged or killed by frost — roughly, anything rated below your area’s winter minimum. Common tender plants in UK gardens: dahlias, cannas, begonias (tuberous), gladioli, bananas (Ensete/Musa), tree ferns (fronds hardy, crown needs protection), olives and citrus in pots, pelargoniums (geraniums), fuchsias (tender varieties), agapanthus (some), cordylines (young ones), and most “exotic” impulse buys. Half-hardy plants survive light frosts but not hard ones; hardy plants need nothing.
Know your local frost dates: first frosts typically arrive October–November (earlier in Scotland and inland, later in coastal south-west), last frosts March–May. The RHS publishes regional guidance, and your own garden’s microclimate matters — a sheltered walled garden can be a full hardiness zone warmer than an exposed hilltop. When in doubt, protect: the cost of unnecessary fleece is pennies, the cost of a dead olive is £80.
Strategy 1: Move Them Indoors
The safest option for the most tender plants: pelargoniums, citrus, tender fuchsias, and anything in pots. The ideal is a frost-free, light, cool space — an unheated greenhouse, conservatory, or bright porch kept above 1–5°C. Cool matters: warm centrally-heated rooms cause weak leggy growth and pest explosions; plants want dormancy, not a second summer.
Before moving in: inspect for pests (greenfly, red spider mite — treat now, not in January when they have colonised the windowsill), cut back leggy growth by about a third, reduce watering sharply (most overwintering plants want barely-moist, not wet — overwatering indoors kills more than cold does), and ensure good air circulation to prevent mould. Check monthly through winter: water sparingly only when dry, remove dead leaves, watch for pests. A good garden shed can work for dormant plants if it stays frost-free — insulate with bubble wrap and add a small frost-guard heater on a thermostat for the coldest nights.
Strategy 2: Lift and Store Dormant Plants
Dahlias, cannas, begonias and gladioli are best lifted after the first frost blackens their foliage: cut stems to ~15cm, lift carefully, dry for a few days, remove loose soil, and store the tubers/corms in trays of barely-damp compost, sand or vermiculite in a frost-free, dark place (shed, garage, under-stairs cupboard) at 5–10°C. Check monthly for rot or shrivelling — remove affected tubers immediately, mist lightly if shrivelling.
The common failure is storing too wet (rot) or too warm and light (premature sprouting in February, producing weak growth). Label everything — every gardener has planted a tray of mystery tubers in spring. Start them back into growth in March–April in pots indoors, planting out only after the last frost. This method is reliable, cheap, and the reason Victorian gardeners grew such spectacular dahlias.
Strategy 3: Protect In Situ
For plants too big to move — tree ferns, cordylines, olives in the ground, agapanthus — protection where they stand. The techniques: mulch crowns deeply (15–20cm of bark, straw or compost) after the first frost; wrap trunks and crowns with horticultural fleece (several layers, tied securely — fleece breathes, unlike plastic which cooks plants on sunny days and traps moisture); pack tree-fern crowns with straw before wrapping; and move vulnerable pots against the house wall under the eaves (the warmest, driest spot).
Fleece is the overwintering hero: cheap, reusable for years, and effective to several degrees below freezing. Buy a big roll in autumn — every garden centre stocks it, and it sells out before the first hard frost. For pots, wrap the pot itself (roots are less hardy than tops — a plant hardy in the ground may die in a frozen pot) or group pots together and wrap the group. Which? tests garden protection products if you want comparisons.
Timing and the Mistakes That Kill Plants
Act on forecasts, not the calendar: the first hard frost warning is your deadline for lifting and moving, not “sometime in November.” But do not rush tender plants indoors in September either — they benefit from autumn light and cool (not freezing) temperatures that harden growth. The sweet spot is after the first light frosts, before the first hard freeze.
The biggest killers, ranked: doing nothing (optimism is not insulation); overwatering indoors (dormant plants in wet compost rot — when in doubt, do not water); wrapping in plastic (condensation, mould, cooking on sunny winter days — always use breathable fleece); bringing plants into hot rooms (weak growth, pests); and planting out too early in spring (one late May frost undoes the whole winter’s work — harden off gradually and watch forecasts). Get these right and your success rate soars. For wider garden planning, see starting a vegetable garden and making your garden look nice cheaply. BBC Gardeners’ World offers seasonal reminders throughout autumn.
Spring: Bringing Them Back Out
Overwintering is only half the job — spring reintroduction kills almost as many plants as winter neglect. The rules: wait until after the last frost (not the average last frost — the actual forecast; a single late May frost undoes everything), harden off gradually (a week of increasing outdoor time, starting with sheltered daytime hours), and resume watering and feeding progressively as growth restarts. For lifted tubers, start them in pots indoors in March–April so they are sturdy plants by planting-out time, not fragile sprouts meeting the real world for the first time.
Resist the spring tidy-up urge with in-situ protected plants: leave fleece on until nights are reliably frost-free, remove winter mulch gradually rather than all at once, and inspect for damage before assuming the worst — many apparently dead plants resprout from the base weeks later. Patience in May saves replacements in June.
Conclusion
Overwinter tender plants by choosing the right strategy per plant: move the most tender indoors to a cool, light, frost-free space with minimal water; lift and store dormant tubers dry and dark at 5–10°C; protect the rest in situ with deep mulch and breathable fleece. Time it to the first frost warnings, avoid the classic killers (overwatering, plastic wrapping, hot rooms, early planting-out), and your dahlias, olives and bananas will greet spring alive.
Frequently Asked Questions
When should I bring tender plants inside?
After the first light frosts but before the first hard freeze — typically October–November depending on region. Watch forecasts rather than the calendar.
Can I leave dahlias in the ground over winter?
In mild coastal areas with heavy mulching, sometimes — but lifting and storing is far more reliable across most of the UK. One hard winter can wipe out an in-ground collection.
What temperature kills tender plants?
Most tender plants are damaged below 0°C and killed by sustained -2 to -5°C. Half-hardy plants tolerate light frosts (-1 to -3°C briefly) but not hard freezes.
Is fleece or plastic better for wrapping plants?
Fleece, always — it breathes, insulates and can stay on for weeks. Plastic traps moisture (causing rot and mould) and overheats plants on sunny winter days.
