Hardy or Tender? What Survives a Frost

Every autumn the first frost sorts a garden into two halves. Some plants come through it looking exactly the same. Others collapse overnight into black, soggy leaves. Which half a plant is in is its hardiness, and knowing it tells you what to cover, what to bring in, and what you can simply leave alone.

This guide explains the words you'll see on seed packets and plant labels (hardy, half-hardy, tender) and the RHS's more detailed H1a to H7 scale, then sorts the common UK crops and garden plants so you know where yours stand before the frost arrives.

Hardy, half-hardy and tender

Gardeners have long sorted plants into three rough groups. They're the words you'll see most, and for everyday growing they're all you need. The hardiness glossary entry has the short definition; here's what each means in practice.

Hardy plants survive frost and cold outdoors all year. You plant them, and they're still there in spring. In the veg garden that means kale, leeks, parsnips, Brussels sprouts, winter cabbage, garlic and overwintering broad beans. Many of them taste sweeter after a frost.

Half-hardy plants cope with cool weather but not a hard frost. They go out once the frosts are over and finish in autumn. Courgettes, French beans and a lot of summer bedding fall here.

Tender plants need warmth and no frost at all. A single frosty night kills or badly damages them, and many sulk in cold well above freezing. Tender crops include tomatoes, peppers, chillies, aubergines and basil.

The line that matters most is the frost line. Half-hardy and tender plants both need to wait for your last frost in spring and come in (or be written off) before your first frost in autumn. The frost date checker shows when both typically fall where you live.

The RHS hardiness ratings, H1a to H7

The Royal Horticultural Society uses a more detailed scale, which you'll see on plant labels in garden centres and on the RHS's own plant pages. Each rating is a band of the lowest winter temperature a plant can take. These are the bands as the RHS hardiness rating page gives them:

The "plain English" column is our summary, not the RHS's wording. The RHS page gives each band its own short description, and is worth reading if you're choosing ornamental plants.

Two things are worth knowing about the scale:

• It's about the coldest night, not the average. A plant rated H3 might sail through ten mild winters and then die in the eleventh, when one night drops lower than usual.
• The useful line for most gardens is around H3. Plants rated H1a to H2 aren't frost-hardy at all: they're the "tender" group above, and they need to come in. H3 plants are the borderline ones, worth a sheltered spot, a mulch or a fleece on the coldest nights. From H4 up, in most UK gardens, you can leave them be.

Which common plants are which

Here are the plants most UK growers ask about, sorted by how they cope with frost. This is general guidance: varieties differ, and a label with an RHS rating on it trumps a list like this.

Tender: bring in, or treat as a summer crop

• Tomatoes, peppers, chillies and aubergines. Killed by frost. Grow them as summer crops, or bring a favourite chilli plant indoors: see overwintering chillies.
• Basil. Blackens in cold well before frost. A windowsill plant from autumn on.
• Cucumbers, sweetcorn and squash. Finished by the first frost; harvest before it.
• Dahlias. The leaves blacken in the first frost; the tubers underground can be lifted and stored.
• Pelargoniums (the "geraniums" of summer pots) and tender fuchsias. Need a frost-free place over winter. Overwintering tender plants covers all three.
• Citrus and most houseplants you put outside for the summer.

Half-hardy: out after the last frost, in before the first

• Courgettes, marrows, French and runner beans. Go out once frosts are over; finished when they return.
• Most summer bedding, such as petunias and busy lizzies.

Borderline: usually fine, worth help in a hard winter

• Rosemary, sage, thyme and oregano. Most established plants are hardy enough in a normal UK winter, but they hate winter wet. Drainage protects them better than fleece. See overwintering Mediterranean herbs.
• Some fuchsias. Hardy shrub fuchsias stay out all year; trailing and bedding kinds are tender. Check the label.
• Young plants of anything. Even a hardy crop is more vulnerable as a seedling.

Hardy: leave them out

• Kale, leeks, parsnips, Brussels sprouts, swede and winter cabbage. Stand in the ground through winter; lift as you need them.
• Garlic and autumn onion sets. Actually need the cold: garlic forms a proper bulb of cloves only after a cold spell. See planting garlic in autumn or spring.
• Overwintering broad beans, sown in autumn. See sowing broad beans in autumn.
• Fruit bushes and trees, such as apples, currants, gooseberries and rhubarb. The plants are hardy; it's spring blossom that a late frost can catch.
• Chives and mint, which die back and return in spring.

What makes a plant more (or less) hardy

A rating tells you how much cold a plant can take in good conditions. In your garden, a few things push that up or down.

Wet. Cold, waterlogged roots kill plants that would survive the same cold in dry soil. That's why Mediterranean herbs die in a soggy winter, and why good drainage counts for as much as shelter.

Pots. In the ground, roots are insulated by the soil around them. In a pot, they're surrounded by cold air on every side and can freeze solid. A plant that's hardy in a border can die in a container. Protecting pots and containers from frost explains how to help them.

Shelter and position. A spot against a south-facing wall stays warmer than an open, windswept bed. Frost pockets (hollows and the bottoms of slopes, where cold air settles) are colder than the rest of the garden.

Age and softness. Young plants, and the soft, sappy growth that late feeding pushes out, are the first to blacken. Established plants that have slowed down for winter are tougher. Gradually hardening off seedlings in spring toughens them for the same reason.

Cover. Fleece, a cloche or a cold frame can carry a borderline plant through a cold night. It won't save a tender one through a whole winter outdoors. How to protect plants from frost explains what each cover can and can't do.

What to do with this

Before the first frost, walk round the garden and sort what you're growing into the groups above:

1. Tender plants: pick the crops, then bring in anything you want to keep.
2. Borderline plants: give them the best spot you have, good drainage, and fleece on hard nights.
3. Hardy plants: leave them to it.

What to do before the first frost turns that into a week-by-week checklist, and the frost date checker tells you how long you've got.