How to Overwinter Tender Plants When You're Short on Space

The frost question

Somewhere between now and November, depending on where you live and how autumn develops, the first frost will arrive.

Tender plants need a plan before it does.

The RHS advises protecting tender plants at the first warning of frost, usually between September and November. Its advice on overwintering tender plants by lifting and mulching covers the timing in detail. That makes September the useful planning month, even if your garden is still looking distinctly summery.

The standard solution is straightforward if you own a greenhouse. Lift the plants. Bring them under glass. Keep them frost-free until spring.

If your growing space consists of a balcony, courtyard, patio or small garden and your winter storage consists of a windowsill and perhaps a shed, that advice becomes considerably less helpful.

The question isn't simply how do I overwinter my tender plants? It's which bits of them actually need saving?

That changes things.

Don't find room for the whole plant if a cutting will do

This is probably the most useful trick for a small-space gardener.

Many tender perennials can be propagated from cuttings before winter, allowing you to preserve a plant without finding indoor space for the mature specimen.

Pelargoniums are an obvious example. Tender fuchsias can be propagated too, as can suitable tender salvias and a range of other perennial plants.

There is another advantage beyond space. Older plants of some tender perennials can become increasingly woody with age, and the RHS notes that young plants raised from cuttings can be preferable to repeatedly retaining ageing parent plants.

So taking cuttings isn't simply the emergency option for people who don't own a greenhouse. It can be a sensible way of renewing your plants at the same time.

A mature container plant might occupy a substantial section of a windowsill or frost-free room. Several young cuttings occupy very little. Keep the varieties you actually care about and let propagation do the space-saving.

Our propagation guide covers the technique properly, but the principle is simple: choose healthy non-flowering growth, prepare the cutting correctly for the plant you're propagating and establish it in a suitable free-draining growing medium.

Pelargoniums are particularly convenient because their cuttings generally don't need the humid enclosed conditions used for many other softwood cuttings.

Once rooted, keep young plants somewhere bright and frost-free. A cool, bright spare room or windowsill can often be more useful than a very warm living room, where low winter light combined with high temperatures can encourage weak growth.

Dahlias: you don't need to keep the plant growing

Dahlias offer a different solution. The part you need to preserve is underground.

Once frost has blackened the foliage, the tubers can be lifted for winter storage. Cut back the stems, lift carefully to avoid damaging the tubers and remove loose soil before storing them somewhere cool, dry and frost-free.

A frost-free garage, shed or cool porch can work. A warm cupboard inside a centrally heated house is less suitable simply because it may be considerably warmer than necessary.

Dormant tubers don't need light. Check them occasionally through winter and remove anything showing serious rot before it affects neighbouring material.

There is an even easier option for container-grown dahlias. If the pots themselves can be moved somewhere frost-free and protected from excessive winter wet, you can leave the tubers in their containers rather than lifting them individually. For a small collection, that may be considerably less work.

The important thing is that the tubers don't freeze and aren't left sitting saturated through winter.

Cannas are slightly different

Cannas also have underground storage organs, rhizomes, but don't treat them exactly like dahlias.

You don't need to wait for frost to damage the foliage before deciding what to do.

In colder or exposed gardens, container-grown cannas can be moved under cover as temperatures fall. Alternatively, the rhizomes can be lifted and stored frost-free for winter.

Again, this is useful for small-space growers because a large summer plant can become a comparatively compact dormant rhizome.

That's the general strategy worth remembering: if a plant can spend winter dormant, don't devote valuable indoor growing space to keeping its summer foliage alive.

Some plants just need a better position

Not every pot needs to come indoors.

Some plants are hardy enough to remain outside but become more vulnerable because they're growing in containers. Roots in pots are more exposed to fluctuating temperatures than roots protected by a large volume of ground.

So for plants that are reasonably hardy but would benefit from some protection, improve the position first.

Move containers away from the most exposed part of a balcony or patio. A sheltered position beside the house can reduce exposure to wind and frost. Group containers where practical to give them some mutual shelter. Raise pots on feet if drainage is poor so that the compost doesn't remain saturated through wet winter weather.

And protect the container itself where necessary. Insulating material such as bubble wrap around a pot can help protect the root zone, and hessian can be used over the top if you don't want to look at bubble wrap all winter. The RHS guide to overwintering tender plants by wrapping explains the technique.

Fleece serves a different purpose: it protects the above-ground plant during cold spells. It doesn't necessarily need to remain wrapped around a plant throughout winter, so remove or loosen temporary protection during milder weather where appropriate.

Reduce the feeding

Plants entering dormancy or much slower winter growth don't need to be pushed into producing soft new growth. So as your tender plants slow down, stop routine feeding — our guide to feeding plants properly explains why growth rate should drive the routine.

Watering should reduce too. A plant using very little water can sit in wet compost for a long time, and excessive winter moisture is a common reason overwintered plants fail.

That doesn't mean letting every plant become completely dry. Cuttings and plants retaining active foliage still need appropriate moisture.

The point is to respond to the plant's growth rather than continuing the summer routine because Thursday has always been watering day. A pelargonium sitting somewhere cool in December isn't using water at anything like its July rate.

Check the compost before watering. If in doubt, our guide on how to water plants properly covers the finger test.

Don't cut everything back

Autumn creates a powerful urge to tidy. Resist some of it.

The RHS advises leaving the previous season's growth on certain more tender plants until spring, with penstemons being a familiar example. The old stems provide some protection to the plant beneath during winter.

Cutting everything neatly to ground level in September can therefore remove useful protection just before the plant needs it. For borderline-hardy plants remaining outdoors, spring is often the better time for the major cut-back.

The dead stems may not be beautiful. They have a job.

Decide what's actually worth saving

This is the part that matters most if you genuinely don't have much room.

You don't have to overwinter everything.

Some plants deserve the effort. A named variety that's difficult to replace. A plant with sentimental value. Something expensive. A particularly good specimen. A variety you've grown for several years and know performs well in your conditions.

Those are easy decisions.

The tray of inexpensive bedding plants bought on impulse in May is different. Yes, you may be able to keep every pelargonium alive until next year. That doesn't automatically mean you should.

If saving twelve mature plants means every windowsill in the house is crowded from October until April, take cuttings from the two or three you actually want and reclaim the space.

Likewise, don't devote six months of care to a plant that struggled all summer and wasn't particularly good when conditions were favourable.

Small-space gardening is partly about editing. Winter makes you do it honestly.

Work out what your frost-free space actually is

Before moving anything, identify the spaces available to you.

A bright windowsill? Useful for cuttings and small plants.

A cool spare room? Potentially excellent for plants that need light but don't need tropical warmth.

A frost-free garage? Useful for dormant material and plants that don't need to remain actively growing.

A shed? Only if it genuinely remains frost-free. A thin-walled garden shed can become almost as cold as the garden outside.

A sheltered outdoor wall? Useful for hardier container plants that need protection from exposure rather than indoor conditions.

The important distinction is between frost-free and simply under cover. A roof stops rain. It doesn't necessarily stop freezing temperatures.

What to do this month

Start with an audit. Walk around the garden, patio or balcony and identify the plants that are genuinely tender. Pelargoniums, tender fuchsias, dahlias, cannas, begonias and tender salvias are obvious candidates, but check anything you're uncertain about rather than relying on how exotic it looks.

Then divide them into groups.

Plants worth taking cuttings from. Do those now, while light levels and temperatures still give them a reasonable opportunity to establish.

Plants that will spend winter dormant. Prepare the storage space, but don't necessarily lift them yet. Dahlias can wait until frost blackens the foliage.

Plants that can remain outside with protection. Work out where the sheltered winter position will be and check that pots drain properly — our piece on autumn planting in pots explains why drainage and root exposure matter more in containers.

Plants you aren't keeping. Make that decision now too.

Then reduce feeding as growth slows and start adjusting watering to autumn conditions.

You don't need to carry the entire summer garden through winter. You only need enough living material to start again.