How Do I Protect Tender Plants from Frost and Get Them Through Winter?

Tender plants are those that cannot survive any frost — a single night below 0 °C will kill them. This category includes most of the most productive summer vegetables as well as many ornamentals prized for summer displays. Protecting them through late autumn and getting them safely through winter is a core skill for any gardener wanting to maintain a continuous growing programme.

What Counts as a Tender Plant?

In vegetable growing, the main tender crops are tomatoes, peppers, aubergines, cucumbers, courgettes, squashes, beans (French and runner), basil, and sweet corn. Among ornamentals, dahlias, cannas, gladioli, pelargoniums, salvias from warmer climates, and most tropical-origin houseplants kept outside in summer are tender. The defining characteristic is origin from frost-free climates — these plants have evolved no mechanism to cope with ice formation in their cells.

Short-Term Protection: Covering in Place

For a single cold night forecast with no sustained cold period, covering tender plants in place is the simplest response. Drape horticultural fleece or frost cloth over the plant, ensuring the cover reaches the ground to trap warm air from the soil. Weight or peg edges. For large tender plants in the ground — a dahlia clump, a group of runner beans — use garden canes to support the fleece so it forms a tent rather than lying on the foliage.

Moving Tender Container Plants Under Cover

The great advantage of growing tender plants in containers is mobility. As autumn approaches and nights cool, move pots to a sheltered porch, cold frame, unheated greenhouse, or conservatory on cold nights. A garage (even unheated) provides several degrees of protection against a brief sharp frost and is usually enough for a tender plant in a large pot to survive a UK winter. Make sure plants receive adequate light — too dark and they will drop leaves and weaken, but most tender plants tolerate dim winter conditions in a dormant or semi-dormant state.

End of Season: Cutting Back and Storing

Dahlias, cannas, and gingers should have their top growth cut back after the first frost, then the tubers or rhizomes lifted, dried briefly, and stored in a frost-free location in trays of dry compost or sand. Do not store in airtight containers — moisture builds up and causes rot. A cool but frost-free shed, garage, or cellar at 5–10 °C is ideal. Check monthly through winter and discard any rotting pieces before they spread.

Pelargoniums and Overwintering Bedding Plants

Pelargoniums (commonly called geraniums) are one of the most common tender perennials kept over winter. After flowering, cut back by one third, remove all dead material, and pot up individually. Overwinter in a frost-free greenhouse or cool bright windowsill at 5–10 °C, watering very sparingly (once every three to four weeks). They will look straggly by late winter but rebound vigorously once temperatures rise and days lengthen in March.