As colder weather draws in, you’ll want to ensure your tender plants stay snug and healthy. Pull on a woolly hat and crank up the heating: here are our top tips for preparing plants for winter and keeping indoor and outdoor species in perfect condition until spring.
Understanding overwintering
What is overwintering? As autumn draws in, some plants need protection from cold weather. This generally applies to tender plants (those that won’t survive frost). Often, these plants come from warmer climates and can’t withstand UK winters.
Overwintering is important because frost, snow and fluctuating winter temperatures can affect garden plants in several ways:
- They can damage plant cells
- They make it harder for plants to absorb nutrients and water
- They weaken plants’ immune systems and increase their susceptibility to pests and diseases.
Preparing outdoor plants for winter
Many garden plants will survive the British winter without any extra help, but some species will benefit from a little TLC in autumn to guard against extreme weather. Our overwintering plants guide will talk you through the basics.
Which plants need overwintering?
Tender herbaceous perennials such as dahlias, cannas, gladioli and pelargoniums (often called geraniums) will need protection over winter. Less hardy plants like tree ferns, banana plants and some fuchsia species will also benefit from winter plant care, as will most plants grown in pots and containers.
How to prepare plants ahead of winter
How do you go about protecting plants in winter? There are various ways to ensure tender plants stay snug during the colder months:
- Moving
- Cutting back
- Lifting and storing
- Mulching
- Covering and wrapping.
Moving
Some potted plants will do best indoors or in a warm, sheltered place like a conservatory or a heated or insulated greenhouse. If you are leaving pots outdoors, move them to a sheltered position and raise them on pot feet or bricks to help the water drain and prevent frost damage.
Cutting back
In mild areas or sheltered spots, the base of tender plants can be covered with a thick mulch to insulate the roots. While you can cut plants back before doing this, leaving some dry stems and seed heads will benefit wildlife over winter, offering food and shelter for birds and insects.
Lifting and storing
The tubers, rhizomes and corms of some tender herbaceous perennials like cannas, dahlias, pelargoniums and gladioli can be dug up and stored over winter in a greenhouse or shed, before being planted out again in spring. Alternatively, if you’re already growing these plants in a protected spot, or have lots of them, they can simply be trimmed back, treated to a thick layer of mulch and left in the ground.
Mulching
In very cold parts of the UK, mulch can be used to protect less hardy perennials like fuchsia shrubs, as well as more tender plants.
Garden compost and well-rotted manure are both great organic mulches. You can also use straw or bark chips to insulate the roots of susceptible plants and help the ground retain moisture.
Use a spade to add a layer of your chosen mulch to the soil surface, around the base of the plant. Aim for 5 - 7.5cm of biodegradable mulch to offer the best winter protection.
Mulches benefit your garden in many other ways, improving the soil structure, suppressing weeds (always a bonus!) and even warming the ground as temperatures rise in spring. Plus, a nice even layer of mulch over your flower beds makes everything look neat and tidy.
Covering and wrapping
How to overwinter plants that can’t be taken indoors? Some species like tree ferns or banana plants aren’t practical to move so may need wrapping with protective covers like horticultural fleece, hessian or a frost blanket to see them through the worst of the winter.
It’s wise to research how to wrap specific tender plants before setting up winter protection. In general, use canes or supports around your plants and wrap fleece or other materials around these stakes, securing them with string or wire. Pack the inside with insulating straw or bracken to drive off the frosts. Add a waterproof layer on top to prevent the plant from getting wet and rotting. Frames or wigwams can be constructed around smaller shrubs too, to offer shelter from the elements. Frost cloths, burlaps and cloches can also shield tender plants from harsh weather.
Overwintering potted plants
Outdoor container plants will need a helping hand to see them through the coldest months. Waterlogged compost may freeze in a cold spell, damaging the roots and bulbs of your precious pot plants.
Tender plants in pots should be moved to a sheltered spot, ideally indoors, in a conservatory, near a sunny window, or into a heated greenhouse. Any houseplants you’ve brought outdoors for a summer holiday will also need to be moved back inside.
Before bringing plants indoors, give them a quick check for pests and diseases - you don’t want to bring in anything nasty that could spread to other plants.
If you’re leaving any hardy container plants outdoors, make sure they’re raised on pot feet or bricks. This will help excess moisture to drain through. Consider adding a mulch to the top of the pot or putting some fleece or a temporary cover over it during a cold snap.
Overwintering specific plant types
Some of the most common plants that need overwintering in UK gardens include:
Dahlias
Showy dahlias may pep up gardens well into autumn, but some of these tender plants need help to make it through the coldest months.
There’s an age-old debate: lift or leave? While some people choose to cut back dahlia stems and cover the ground with mulch, the RHS advises to lift tubers after the first frost when the leaves have been blackened. Cut flowering stems a few centimeters from the base, then use a fork to prize the tubers out of the ground. Shake off the soil and put them in a cool shed or garage to dry off, before burying them - with the old flower stalks just showing - in a tray filled with dry sand or compost. Plant them back out in spring for another dazzling display in late summer.
Pelargoniums
Some people choose to grow pelargoniums as annual flowers, saving the hassle of overwintering them, but these colorful perennials can be enjoyed year on year. The easiest way to overwinter potted pelargoniums is by bringing them under glass, either into a greenhouse or conservatory.
Alternatively, you can take softwood cuttings in late summer and let them establish on a warm windowsill. Plants in the ground can be lifted and overwintered in a bare-root state. Remove the excess soil and let them dry, before wrapping them in paper and hanging them upside down until spring.
Banana plants
Musa bajoo is a common banana cultivar, often grown in UK gardens. While small plants can be brought indoors or overwintered in a greenhouse, larger trees should be wrapped up before the first frost. Saw off the top of the plants and use canes and chicken wire to construct a frame around the stumps. Pack this with straw, before adding thick plastic over the top as a waterproof cover. Uncover the stumps when all risk of frost has disappeared in spring.
