Temperature divides herbs into two camps: the hardy perennials that survive winter outdoors, and the tender annuals that are killed by the first frost. Rosemary, thyme, sage and chives will stand through a cold winter and come back in spring. Basil is killed by a single light frost, cilantro bolts at the first sign of heat, and lemongrass must be brought under cover before autumn ends. Knowing which camp each herb belongs to is the difference between a herb garden that lasts for years and one that has to be replanted every spring.
This guide covers frost tolerance, heat and bolting, and how to overwinter herbs in cold and mild climates. Use our frost date calculator for your local dates, and check your local extension service for the hardiness guidance that fits your area.
Tender herbs: killed by frost
Tender herbs are the summer annuals. Basil is the most tender of all: it is damaged by temperatures just above freezing and killed by even a light frost, and it sulks badly in cold soil — a basil plant set out too early will sit still for weeks and may never catch up. Lemongrass is similarly tender and must be brought indoors or under cover before the first frost. Cilantro and dill tolerate a light frost once established, but they are grown as annuals and are sown fresh each year. Stevia and borage are also tender and are grown as annuals in most climates.
Sow or plant tender herbs only after all danger of frost has passed and the soil is warm. Start basil indoors a few weeks before the last frost, harden it off, and plant it out when the nights are reliably warm. In autumn, harvest tender herbs before the first frost, or bring them indoors: a pot of basil can live on a sunny windowsill for weeks after the outdoor plants are gone, and lemongrass can be overwintered in a pot in a bright, frost-free place. Keep a fleece handy in spring and autumn, so a forecast frost does not catch your tender herbs unprotected.
Hardy herbs: survivors of winter
Hardy herbs are the perennials that come back year after year. Thyme, sage, oregano, chives and mint are hardy in most temperate climates and will survive winter outdoors, dying back in autumn and regrowing in spring. Rosemary is hardy in mild climates but is damaged by hard frosts in cold areas, especially in wet soil — cold and wet together kill rosemary far more reliably than cold alone. Lavender is hardy in most temperate climates if it is in free-draining soil, but it too suffers in cold, wet winters. Parsley is a biennial: it survives one winter, flowers and sets seed in its second year, and then dies.
Hardy does not mean indestructible. A hardy herb in a pot is more exposed to cold than the same herb in the ground, because the roots are above ground and the compost can freeze solid. Move potted rosemary and lavender against a sheltered wall in winter, wrap the pots in fleece, and raise them off the ground. In the ground, a gravel mulch around Mediterranean herbs keeps the crown dry, which helps them survive a cold, wet winter far more than any amount of covering. Do not feed hardy herbs late in the season — soft new growth is the first thing frost damages.
Heat and bolting
Heat is the other end of the problem, and it affects herbs differently from frost. Cilantro bolts — sends up a flower stalk and stops producing useful leaves — as soon as the weather warms up, and once it has bolted it cannot be reversed. Sow cilantro in spring and again in late summer for an autumn crop, give it afternoon shade, and keep the soil moist. Dill and parsley also bolt in heat, though more slowly than cilantro. Basil flowers in heat, and flowering ends useful leaf production, so pinch the flower buds off as soon as they appear.
Warm-season herbs such as basil and lemongrass love heat and grow fastest in warm weather, but even they wilt in extreme heat and need steady water. Mediterranean herbs such as rosemary, thyme and oregano are naturally heat-tolerant and cope well with hot summers, provided their soil drains freely. In a heatwave, water herbs deeply in the morning, mulch to keep the soil cool, and give soft herbs a little afternoon shade — our guide to mulch types explains the options.
Overwintering herbs
In mild climates, most herbs can be left outside all winter with little protection. In cold climates, tender herbs must come indoors or be treated as annuals, and even hardy herbs need a little help. Bring basil and lemongrass indoors before the first frost, and keep them on a sunny windowsill. Rosemary in a pot can be brought into a cold conservatory or an unheated room with a sunny window — a hot, dry living room is worse for it than a cold, bright one, because dry air makes it drop leaves and attracts spider mites. Thyme, sage and chives can usually stay outside, but protect their pots from freezing solid.
In the ground, leave the foliage of perennial herbs standing over winter — it protects the crown from frost, and it can be cut back in spring. Do not cut rosemary or lavender back hard in autumn, because the new growth will be damaged by frost. In spring, wait until you see new growth before you cut back winter damage, because a stem that looks dead may still be alive at the base. If you are unsure whether a herb will survive winter in your area, check your local extension service for the hardiness guidance that fits your climate.
Microclimates: warm walls and sheltered corners
A garden is not one temperature — it is a patchwork of microclimates, and using them well can extend the herb season by weeks. A south-facing wall stores heat during the day and releases it at night, so herbs planted against it — rosemary is the classic wall herb — survive frosts that kill the same herb in the open garden. A sheltered corner out of the wind is warmer than an exposed bed. A raised bed warms up earlier in spring than ground-level soil. And a cold frame or cloche can keep parsley and chives picking through winter in mild climates.
Use microclimates deliberately. Plant tender herbs in the warmest spot, and hardy herbs where they will get the sun and drainage they need. Avoid frost pockets — low spots where cold air collects on still nights — for tender herbs, and avoid planting rosemary where water collects, because cold and wet together are what kill it. A thermometer in different parts of the garden on a frosty morning will show you the differences, and they are often larger than you would expect.
Common mistakes
The most common temperature mistake is planting basil out before the last frost, so a single cold night kills it. The second is leaving lemongrass outside into autumn and losing it to the first frost. The third is keeping rosemary in a hot, dry living room over winter, where it drops leaves and attracts spider mites — a cold, bright room is better. The fourth is cutting woody herbs back hard in autumn, so soft new growth is damaged by frost. And the fifth is sowing cilantro once in spring and expecting it to last all summer — it bolts in heat, so sow a little every few weeks and again in late summer for autumn.
| Herb | Frost tolerance | Heat tolerance | Overwintering |
|---|---|---|---|
| Basil | None; killed by light frost | Loves heat; wilts if dry | Indoors on a sunny sill; or treat as annual |
| Lemongrass | None; killed by frost | Loves heat | Pot indoors in a bright, frost-free place |
| Cilantro, dill | Light frost once established | Bolts in heat | Sow in spring and late summer; annuals |
| Parsley | Light frost; biennial | Bolts in heat | Survives one winter; flowers in year two |
| Rosemary | Hardy in mild climates; damaged by hard frost | Very heat-tolerant | Outside in mild areas; cold bright room in cold areas |
| Thyme, sage, oregano, chives, mint | Hardy in most temperate climates | Heat-tolerant | Outside; protect pots from freezing solid |
| Lavender | Hardy if soil drains freely | Very heat-tolerant | Outside in free-draining soil; cold and wet kills it |
Frequently asked questions
Which herbs survive winter outside?
Thyme, sage, oregano, chives and mint are hardy in most temperate climates and survive winter outdoors. Rosemary and lavender are hardy in mild climates but suffer in cold, wet winters. Basil and lemongrass are tender and must come indoors before the first frost.
When can I plant basil outside?
Only after all danger of frost has passed and the soil is warm. Basil is damaged by temperatures just above freezing and killed by even a light frost, so harden it off and plant it out when nights are reliably warm.
Why did my cilantro bolt?
Cilantro bolts in heat — it sends up a flower stalk and stops producing useful leaves, and it cannot be reversed. Sow it in cool weather, give it afternoon shade, keep the soil moist, and sow a little every few weeks and again in late summer.
How do I overwinter rosemary?
In mild climates, leave it outside in free-draining soil against a sheltered wall. In cold climates, grow it in a pot and bring it into a cold, bright room — a conservatory or unheated room — for winter. A hot, dry living room makes it drop leaves.
Can herbs grow in a heatwave?
Mediterranean herbs such as rosemary, thyme and oregano cope well with heat if their soil drains freely. Basil and lemongrass love warmth but need steady water. Soft herbs such as cilantro and parsley bolt in heat — give them afternoon shade and mulch to keep the soil cool.