Overwintering is the practice of keeping plants alive through winter so they grow again in spring — bringing tender plants indoors, protecting hardy plants in the ground, and storing bulbs, tubers, and container plants where the cold cannot kill them. It is the skill that turns annual spending on new plants into a garden that returns each year, and it is mostly a matter of knowing what each plant needs and giving it to it before the first hard frost. This guide explains what overwinters where, how to protect plants in the ground, how to bring tender plants indoors, and how to store bulbs and tubers through winter.
The first thing to understand is that overwintering is different for every plant, and the difference is hardiness: how much cold a plant can survive. A plant that is hardy in your zone can stay outside with a little protection. A plant that is tender in your zone must come indoors or be stored. And a plant that is borderline may survive a mild winter outside and die in a cold one. Knowing your zone, and knowing which of your plants are hardy in it, is the foundation of overwintering. Check your zone pages in our planting calendar and, if you are unsure about a plant's hardiness in your area, check your local extension service.
What overwinters where, by zone band
In the coldest zones, roughly zones 3–5, winter is long and hard, and only the hardiest perennials, shrubs, and trees survive outdoors without serious protection. Tender plants must come indoors or be stored, hardy plants need a thick mulch layer, and container plants need to be brought into shelter, since a pot freezes far harder than the ground. In the middle zones, roughly zones 6–8, many perennials and shrubs survive outdoors with mulch and a little protection, tender plants still need shelter, and hardy vegetables such as kale and leeks can be harvested through winter under cover.
In the mild zones, roughly zones 9–10, frosts are light and short, and many plants that are tender elsewhere survive outdoors with a row cover or a mulch layer on cold nights. Tender perennials, citrus, and tropical plants still need protection on the coldest nights, and container plants should be moved to a sheltered spot. In frost-free zones 11–13, overwintering is hardly needed at all: the garden grows year-round, and the work is managing heat and rain rather than cold. The pattern is simple: the colder your zone, the more you bring in and the more you protect.
Protecting plants in the ground
Hardy perennials, shrubs, and trees that stay outside need their roots protected. A thick mulch layer around the base insulates the soil, keeps it from freezing and thawing repeatedly, and stops the freeze-thaw heaving that pushes shallow-rooted plants out of the ground. See our mulch gardening and fall mulching guide guides for mulching. Keep the mulch away from the stems and trunks themselves, so bark stays dry and rot does not set in.
Tender shrubs and perennials that are borderline in your zone can be protected with fleece, burlap, or straw wrapped around them, and with a mulch mound over the crown. Roses can be mounded with soil or compost over the graft, and vulnerable shrubs can be wrapped loosely in fleece on the coldest nights. Water the soil before a hard frost, since damp soil holds warmth better than dry soil, and do not prune tender plants in fall — the top growth, even if it dies back, protects the crown, and pruning should wait until spring. See our winter gardening guide for the cold season in detail.
Bringing tender plants indoors
Tender plants that cannot survive your winter — many herbs, geraniums, citrus, tropical houseplants, and tender perennials — should be brought indoors before the first hard frost, not after it. Check them for pests first, since bringing pests indoors is a common mistake, and pot them up if they are in the ground. Give them the brightest spot you have, water sparingly through winter, since growth slows and the soil dries slowly indoors, and keep them away from radiators and cold draughts.
Container plants are the most vulnerable of all, because a pot has far less soil than the ground and freezes through quickly. Bring containers into a frost-free shed, garage, or greenhouse, or cluster them together against a sheltered wall and wrap the pots in bubble wrap or hessian. Even hardy plants in pots need protection in cold zones, since their roots are exposed to the cold in a way that roots in the ground are not. Our container gardening guide covers container care, and our season extension guide covers shelters.
Storing bulbs, tubers, and roots
Some plants overwinter best out of the ground, stored cool and dry. Tender bulbs and tubers such as dahlias, cannas, and gladioli should be lifted after the first light frost, dried, cleaned of soil, and stored in a cool, frost-free, ventilated place — in boxes of dry compost, sand, or shredded paper — where they will not rot or dry out completely. Check them through winter, removing any that are soft or mouldy before they affect the rest.
Hardy bulbs such as tulips, daffodils, and garlic stay in the ground over winter, and they need the cold to flower or grow well in spring. Root crops such as carrots and parsnips can be left in the ground under a thick mulch and dug as needed, provided the ground does not freeze solid — see our harvest storage guide for storing the harvest. And perennials that die back in winter need no storage at all: their roots survive underground, and they return in spring, especially if they are mulched.
Spring: bringing plants back out
Overwintering ends in spring, when the frost risk has passed and plants can go back outside. Harden tender plants off gradually — a week or so of longer spells outdoors in shelter — before planting them out, since a plant moved straight from indoors to the open garden will check or die. Unwrap protected shrubs, remove winter mulch from the crowns of perennials so new growth can come through, and check stored bulbs and tubers for shoots before planting them out. See our spring gardening guide for the season, and keep a record of what survived, what did not, and what you will do differently — our garden journal guide explains how that record pays off next winter.
Common mistakes
The most common mistake is leaving tender plants out until the first hard frost, when it is too late. The second is bringing pests indoors with the plants — check them first. The third is overwatering indoor plants through winter, when they need far less water. The fourth is leaving container plants outside in cold zones, where their pots freeze through. The fifth is piling mulch against stems and trunks, which causes rot. And the sixth is pruning tender plants in fall, removing the growth that would have protected the crown. Bring tender plants in early, check for pests, water sparingly, protect containers, and prune in spring.
Frequently asked questions
When should I bring tender plants indoors?
Before the first hard frost, not after it. Watch the forecast through fall, and bring tender plants in while the weather is still mild, so they adjust to indoors without a cold shock.
Can I overwinter plants in a garage?
Yes, if the garage stays frost-free and the plants get some light. A garage suits dormant bulbs, tubers, and container plants, but leafy plants that are still growing need a bright spot, such as a windowsill or a greenhouse.
How do I store dahlia tubers over winter?
Lift them after the first light frost, dry them, clean off the soil, and store them in a cool, frost-free, ventilated place in boxes of dry compost, sand, or shredded paper. Check them through winter and remove any that are soft or mouldy.
Will mulch alone protect a tender plant?
No — mulch protects roots, but it will not save a tender plant from a hard frost. Tender plants need shelter indoors, in a greenhouse, or under a heavy cover, and mulch is a complement to that, not a substitute.
What overwinters in zones 11–13?
In frost-free zones 11–13, almost everything overwinters outdoors, since there is no frost to survive. The work there is managing heat, rain, and pests rather than cold, and the garden grows year-round. If you are unsure about a plant's hardiness in your zone, check your local extension service.