Many herbs look finished once cold weather sets in. Often the roots underneath are still alive. Overwintering means protecting hardy herbs where they stand, and lifting tender ones into pots before hard frost. Sorting your herbs correctly matters more than any single technique below.
What you need
Gather these before the weather turns:
- Sharp pruners or scissors
- Mulch such as straw, bark chips or shredded leaves, 3 to 4 inches (8 to 10 cm) deep
- Pots with drainage holes, one per tender herb you plan to lift
- Fresh potting mix
- A hand trowel or fork for lifting root balls
- A bright windowsill or a cool, frost-free room for winter
- Your average first frost date
When to overwinter perennial herbs
Start once nights regularly dip toward freezing. Act before a hard frost blackens leaves. Hardy perennials tolerate a light frost or two without harm. Sage, thyme and oregano are common examples. Chives and most mints qualify too. There is no need to rush them at the first cool night. Tender perennials cannot survive freezing ground. This is why rosemary, bay and lemon verbena are usually grown as annuals in cold climates. Lift these before the first hard frost is forecast. Don't wait until after it happens. If you are unsure how cold your winters get, check your local frost dates first. The same herb can be a reliable perennial in one climate. In another climate, it may only survive as a tender annual.
Step 1: Sort your herbs into hardy and tender
Walk your herb bed and sort each plant into two groups. Do this before anything else. Hardy perennial herbs have tough or woody roots that survive freezing ground in most climates. Sage, thyme and oregano are common examples. Marjoram and chives are two more. Mint, peppermint and catnip round out the list. Winter savory also qualifies. Left in place with a little protection, these herbs die back on top. They resprout from the base each spring. Tender perennials are usually grown as annuals in cold gardens, because their roots cannot survive a hard freeze. Rosemary and bay are two examples. Lemon verbena and scented geranium are two more. This holds true across most areas. Mild, frost-free climates are the exception. There, some tender types survive outdoors all year. Weigh this list against your own conditions, and don't follow it blindly. Getting the sorting right matters more than anything else here. A hardy herb left in the ground usually needs only mulch. A tender one left in the ground is likely to die.
Step 2: Cut back stems at the right time
Once top growth has been touched by a light frost, cut hardy perennial herbs back. Remove about one-third to one-half of their height. Use clean, sharp pruners. Make each cut just above a set of leaves or a bud. Leave woody-based herbs like sage and thyme with some green growth. Bare, leafless wood is slower to resprout in spring. Soft-stemmed herbs like mint and catnip tolerate a harder cut, closer to ground level. They regrow readily from the roots. Hold off on cutting back tender perennials you plan to lift. Prune these only lightly until they are settled indoors. Cutting back removes the soft growth that winter wind and cold damage most easily. It also makes mulching the crown afterward much easier.
Step 3: Mulch the roots of in-ground herbs
After cutting back, spread mulch over the root zone of every hardy perennial herb staying in the ground. Aim for a layer 3 to 4 inches (8 to 10 cm) deep. Straw, shredded leaves and bark chips all work well. Keep the mulch a couple of inches (about 5 cm) clear of the crown. This stops the base of the plant sitting in constant damp. Mulch insulates the soil and buffers roots against sharp temperature swings. It also reduces freeze-thaw heaving, which can push shallow-rooted herbs like thyme and chives partly out of the ground. In an exposed spot, add a loose layer of evergreen boughs or horticultural fleece over the mulch. Leave the mulch in place through winter. Pull it back gradually as new growth appears in spring.
Step 4: Lift tender perennials into pots
Before the first hard frost, dig around each tender perennial with a trowel or fork. Keep as much of the root ball intact as you can. Choose a pot only slightly larger than the root ball. Make sure it has drainage holes. Settle the plant in with fresh potting mix, then water well. Let the pot drain fully before moving it anywhere. Lifting is easiest with herbs that were already container-grown over summer. You can simply bring the whole pot indoors. Herbs grown directly in soil suffer some root disturbance. Handle them gently while firming them into their new pot. Trim off any damaged or overly long stems at this point. Avoid heavy pruning, though. The plant needs its remaining leaves to keep growing indoors.
Step 5: Settle potted herbs indoors for winter
Place lifted pots in the brightest spot you have, ideally a south-facing windowsill. Keep them in a cool room rather than next to a heat source. Most tender herbs are comfortable at 55-65°F (13-18°C) over winter. Warmer, drier indoor air pushes them to stretch and drop leaves. Water only when the top inch (2.5 cm) of soil feels dry. Overwatering in low winter light is a more common cause of loss than underwatering. Turn pots roughly once a week if light comes mainly from one direction. This keeps growth even on all sides. Expect growth to slow right down over winter. This is normal. Potted herbs are not meant to put on much new size until spring returns.
Common problems
Leaves turn black and mushy after a frost
This is frost damage, not disease. It usually affects only the soft top growth that was not yet cut back or protected. Leave the blackened material in place until the thaw. It offers a little extra insulation to the crown below. Trim it away once temperatures settle. Most hardy perennial herbs resprout from lower down the stem or from the base. Lasting harm is rare.
Bare stems show no new growth by mid-spring
Scratch a stem lightly with a fingernail. Green tissue just under the bark means the plant is simply slow to wake up. Dry, brittle wood means that part has died. This can affect a single stem or the whole plant. Give woody herbs like sage and thyme extra weeks of settled warmth. They are often the last herbs in the garden to show fresh growth.
Potted herbs wilt and drop leaves indoors
This is usually a reaction to the move, not a sign of a sick plant. Lower light, drier air and a warm room together stress a herb that spent summer outdoors. Move the pot to the brightest spot available. Keep it away from radiators and heating vents. Water only when the top inch (2.5 cm) of soil is dry. Some leaf drop in the first few weeks indoors is normal. Most plants settle once they adjust.
Plants heave partly out of the soil in late winter
Repeated freezing and thawing can push shallow-rooted herbs upward. Thyme and chives are especially prone to this. It exposes roots to cold, drying air. Firm the plant gently back into place by hand as soon as the soil is workable. Top up the mulch layer afterward, to cushion it against further heaving.
What to do next
Once nighttime temperatures settle reliably above freezing, start hardening off any indoor herbs. Set them outside for a few hours a day, increasing the time gradually over one to two weeks. Pull mulch back from hardy perennials as fresh growth appears at the base. Feed all your overwintered herbs lightly once they are growing strongly again, to support healthy new leaves.