How to overwinter tender perennials
Tender perennials, such as pelargoniums, fuchsias, osteospermums and marguerites look great all summer, but unless they are given protection from the harsh winter weather, they will need to be replaced each spring. If you can do this, they will last for years, indeed many will put on even better display in their second and third years. If you have limited space for overwintering plants, make it a priority to save those which are expensive to buy, such as pelargoniums and standard fuchsias, as well as anything unusual that might be difficult to find the following spring. After that, choose favourite plants and flower colours so you can continually improve your summer border displays year on year. There are a range of techniques on how to overwinter tender perennials,which will depend largely on the plants themselves.
Here’s my plant-by-plant survival guide:
Agastache ‘Blue Fortune’
In mild gardens they can be overwintered outside if you protect the roots with piles of dry leaves, composted bark or straw. If you want the whole plant to survive, overwinter it somewhere the temperature doesn't fall below 5°C. Pot it up individually and place it on a windowsill of a cool room, or place it under the staging in a heated conservatory or greenhouse.
Arctotis x hybrida
These fiery African daisies produce flowers from July to September and make long-lasting container plants for a sunny patio or courtyard garden. They are very tender and prone to basal rotting in winter so need to be kept somewhere the temperature doesn't fall below 5°C – use a max/min thermometer to keep track. They can either be potted up individually and placed on a windowsill of a cool room, or placed in a well-lit, but shaded position in a heated conservatory or greenhouse.
Argyranthemum (marguerite)
Marguerites can be overwintered in several ways, but they must be kept frost free, Ideally, don’t allow the temperature fall below 5°C. You can keep one or two flowering all winter by placing them in a heated greenhouse or conservatory. Otherwise, they can either be potted up individually and placed on the windowsill of a cool room, or placed under the staging in a heated conservatory or greenhouse. Alternatively, you can save space by packing several plants into tray. Lift the plants and cut back the stems before placing them in a crate topped up with just-moist compost. I successfully overwinter standards by trimming back this year's growth by about one-third and keep plants ticking over during the winter by placing them in a greenhouse with a minimum temperature of 5°C. You can also take cuttings now as insurance, kept at a minimum temperature of 7°C.
Begonia
Tuberous begonias are best lifted before the first frost and cut back to 10cm. The stems will dry and naturally fall from the tubers, which can then be boxed up in just-moist compost and placed somewhere the temperature doesn't fall below 5°C. Fibrous-rooted begonias are best overwintered as ‘dormant’ plants. Pot them up individually, cut back to 15cm and place on a windowsill of a cool room, or under the staging in a heated conservatory or greenhouse with a minimum temperature 5°C. You can also take cuttings now as insurance and keep them at a minimum temperature of 7°C.
Brachyscome multifida
This slightly tender perennial with pretty flowers and finely divided foliage can also be overwintered successfully somewhere the temperature doesn't fall below 5°C. Before the temperatures get too low in early autumn, either pot-up plants individually and place them on the windowsill of a cool room, or under the staging in a heated conservatory or greenhouse. In milder areas you might get away with overwintering plants in a well-insulated coldframe or greenhouse. You can also take cuttings now as insurance if they are kept at a minimum temperature of 7°C.
Calceolaria integrifolia (slipper flower)
If your soil is not too cold or wet in winter, calceolarias will survive outside in a sunny, sheltered spot. Cut back the top growth to 15cm and protect the roots and basal buds with a thick layer of manure or bark chippings. Uncover the plants in early spring when the worst of the frosts are over. Elsewhere, cut back hard after lifting and store in crates of just-moist compost placed somewhere cool, well-lit and frost free. You can also take cuttings now as insurance if they are kept at a minimum temperature of 7°C.
Canna (Indian shot)
In mild areas with free-draining soil, Indian shot plants can be left to overwinter in the ground, but in colder regions these half-hardy perennials need to be lifted and stored to protect them from the worst winter weather. Do this as soon as the first frosts have burnt the leaves black, then cut back the top-growth to 15cm and lift the plants from the ground. Clean off as much soil as possible before trimming any straggly, fine roots. Store them in boxes of dry compost to overwinter them in the garage, although any cool but frost-free place would do. The tubers are replanted in the spring once the danger of frosts has passed.
Cineraria maritima
This nearly hardy grey-leaved plant will survive outside in mild, sheltered gardens with well-drained soil if the winter isn’t too bad. It will then flower in its second year and grow into a substantial plant. You can prevent it getting leggy by cutting back the top growth to 15cm and protecting the roots and basal buds with a thick layer of manure or bark chippings. Uncover the plants in early spring when the worst of the frosts are over. In really cold gardens, overwinter by placing it in a coldframe or under the staging in an unheated greenhouse.
Coleus
You either love or hate these colourful foliage plants. They are very easy to raise from seeds or cuttings and can be overwintered successfully if kept where the temperature doesn't fall below 5°C. Either pot them up individually and place on the windowsill of a cool room, or cut back foliage to 15cm and keep under the staging in a heated conservatory or greenhouse.
Cosmos atrosanguineus (chocolate cosmos)
If the soil is not too cold or wet in winter leave in the ground where they have been growing. Cut back the top growth to 10cm and protect the roots and basal buds with a thick layer of manure or bark chippings. Uncover the plants during early spring when the worst of the frosts are over. In colder areas, after the foliage has died back in autumn, reduce the stems to within 5cm of the roots. Lay in a tray of soil or compost and over-winter in a frost-free environment until early spring. Bear in mind new growth does not appear until late spring, so don’t be in a hurry to throw away plants that haven’t sprouted.
Dahlia
Traditional advice dictates that you have to lift dahlias each autumn, but these days less severe winters mean that dahlias can be left to overwinter in the ground in mild areas provided you have free-draining soil. If you have heavy clay, lift these half-hardy perennials and store them to protect them from the worst winter weather as soon as the first frosts have burnt the leaves black. Cut back the top-growth to 15cm and lift the plants from the ground. As much soil as possible should be cleaned off, before trimming any straggly, fine roots. Store them in paper bags or boxes of shredded newspaper or dry compost to overwinter them in the garage, although any cool but frost-free place would do. The tubers are replanted in the spring once the danger of frosts has passed.
Datura (Brugmansia suaveolens)
These stunning trumpet flowers are pretty tough and respond well to being cut back hard. In mild gardens they can be overwintered outside if you protect the roots with piles of dry leaves, composted bark or straw. If you want the whole plant to survive, overwinter it somewhere the temperature doesn't fall below 5°C. Either pot-up individually and place on the windowsill of a cool room, or place under the staging in a heated conservatory or greenhouse.
Diascia
Overwintered plants often put on a better display than new plants, so if your soil is not too cold or wet in winter leave diascias in the ground where they have been growing. Cut back the top growth to 15cm and protect the roots and basal buds with a thick layer of manure or bark chippings. Uncover the plants during early spring when the worst of the frosts are over. Elsewhere, keep them somewhere the temperature doesn't fall below 5°C. Such tender plants can either be potted up individually and placed on a windowsill of a cool room, or kept under the staging in a heated conservatory or greenhouse. You can also take cuttings now as insurance, kept at a minimum temperature of 7°C.
Felicia
Felicias are tougher than they look and can be overwintered successfully outside in mild areas provided the soil is not too wet. Variegated varieties are less hardy and so are best overwintered somewhere the temperature doesn't fall below 5°C. All felicias can be kept flowering throughout the winter if you have heated greenhouse or conservatory. In this case, pot up individual plants, trim them lightly and water before placing on a windowsill of a cool room. Lightly trim overwintered plants again during late spring to tidy them up and encourage bushy growth, before planting outside. You can also take cuttings now as insurance kept at a minimum temperature of 7°C.
Fuchsia
Although hardy varieties can be left outside to overwinter, the top growth is likely to be cut back by frosts. So unless you garden in a mild area, it’s worth trimming it in autumn and laying the trimmings over the crown to provide an insulating layer against severe frost. Tender fuchsias can be overwintered outdoors, too, in mild areas, provided the soil is not too cold or wet. Cut back the top growth to 15cm and protect the roots and basal buds with a thick layer of manure or bark chippings. Uncover the plants during early spring when the worst of the frosts are over. Elsewhere, they need to be kept somewhere the temperature doesn't fall below 5°C. Trim back the top growth by about half and pot up individually before placing on the windowsill of a cool room, or in a heated conservatory or greenhouse. You should be able to successfully overwinter standard fuchsias by trimming back this year's growth by about one-third and keeping plants ticking over during the winter by placing them in a greenhouse with a minimum temperature 5°C.
Gazania
These are very tender plants that can’t cope with winter cold or wet, so they need to be kept somewhere the temperature doesn't fall below 7°C. Such tender plants can either be potted up individually and placed on the windowsill of a cool room, or placed under the staging in a heated conservatory or greenhouse. You can also take cuttings now as insurance kept at a minimum temperature of 7°C.
Glechoma hederacea ‘Variegata’
A wonderful trailing plant that can be successfully overwintered by cutting hard back and keeping somewhere the temperature doesn't fall below 0°C. Pot-up individually and either place on a windowsill of a cool room, or under the staging in a heated conservatory or greenhouse. New growth put on in spring can be used for taking cuttings. You can also take cuttings now as insurance – keep them at a minimum temperature of 7°C.
Helichrysum petiolare
This attractive foliage plant doesn't do as well in its second year, so it is only worth overwintering them if you want cutting material in spring. The best way to achieve this is to cut back the plants to 15cm and pot them up individually before placing them on a windowsill of a cool room, or under the staging in a heated conservatory or greenhouse. Maintain a temperature of at least 5°C. During early spring water sparingly and provide a little heat to encourage new shoots that will make excellent cutting material. You can also take cuttings now as insurance kept at a minimum temperature of 7°C.
Impatiens
Plants that are in good condition and free of pests and diseases can be overwintered successfully. If you can maintain a temperature of 13°C you can keep them flowering all winter. Otherwise, a temperature above 7°C will see them through. Pot them up individually and either place them on a windowsill in a cool room, or under the staging in a heated conservatory or greenhouse. You can also take cuttings now as insurance kept at a minimum temperature of 7°C.
Lobelia cardinalis ‘Queen Victoria’
If your soil is not too cold or wet in winter, this wonderful tender perennial will survive outside in a sunny, sheltered spot (provided you can keep the slugs and snails off!). Cut back the top growth to 15cm and protect the roots and basal buds with a thick layer of manure or bark chippings. Uncover the plants in early spring when the worst of the frosts are over. Elsewhere, cut it back hard after lifting and store in crates of just moist compost placed somewhere cool, well-lit and frost free.
Lotus
Two-year-old plants flower much better because most blooms are produced on older wood, so these plants are really worth overwintering. For best results, keep them somewhere the temperature doesn't fall below 7°C. Pot up plants individually without cutting them back and place on a windowsill in a cool room, or on the staging in a heated conservatory or greenhouse.
Melianthus major
In most gardens this half-hardy plant can be overwintered outside if you protect the roots with piles of dry leaves, manure, composted bark or straw. In very exposed gardens protect from cold winds too.
Osteospermum
African daisies can be difficult to overwinter as plants if your soil is heavy. On light soils you can get them through the winter by covering with open-ended cloches. However, on heavy soil you’ll be better off overwintering rooted cuttings. For best results, keep them somewhere the temperature doesn't fall below 5°C – such as on a windowsill of a cool room, or on the staging in a heated conservatory or greenhouse.
Pelargonium (bedding geranium)
These expensive plants need to be kept somewhere the temperature doesn't fall below 5°C. Pot them up individually and either place them on the windowsill of a cool room, or under the staging in a heated conservatory or greenhouse. If you have some larger plants, trim back this year's growth by about one-third and keep plants ticking over during the winter by placing them in a greenhouse with a minimum temperature of 5°C.
Penstemon
Most penstemons can cope with light frosts, although the foliage will be cut back. If the soil is not too cold or wet during the winter, leave them in the ground where they have been growing. Cut back the top growth to 15cm and protect the roots and basal buds with a thick layer of manure or bark chippings. Uncover the plants in early spring when the worst of the frosts are over. Young plants flower better than older ones, so it is worth propagating in spring. Bring overwintered plants into growth during early spring by raising the temperature and giving a little water. You can also take cuttings now as insurance and keep them at a minimum temperature of 7°C.
Salvia
Salvias vary in their hardiness. Half-hardy perennial salvias can be left in the ground where they have been growing if the soil is not too cold or wet in winter. Cut back the top growth to 15cm and protect the roots and basal buds with a thick layer of manure or bark chippings. Uncover the plants in early spring when the worst of the frosts are over.
Scaevola
Young plants flower better than older ones, so it is worth propagating them now and overwintering them as rooted cuttings. Alternatively, overwinter one or two plants and take cuttings in spring. Get plants through the winter by keeping them somewhere the temperature doesn't fall below 5°C. Pot up individually and place either on the windowsill of a cool room, or under the staging in a heated conservatory or greenhouse.
Verbena
Trailing verbenas are nearly all tender perennials so can be successfully overwintered as plants. Get plants through the winter by keeping them somewhere the temperature doesn't fall below 5°C. Pot them up individually and place them either on the windowsill of a cool room, or under the staging in a heated conservatory or greenhouse. Young plants flower better than older ones, so it is worth propagating in spring. Bring overwintered plants into growth during early spring by raising the temperature and giving them a little water. Alternatively, propagate now and overwinter them as rooted cuttings.
Take cuttings as insurance
If you don't have the space to overwinter all your plants, there is still time to take cuttings and root them in a heated propagator or on a sunny windowsill.
Choose healthy looking, non-flowering shoots and trim them to about 5-7cm, long just below a leaf joint.
Remove the lower leaves and any flowerbuds and insert them around the edge of a pot filled with cuttings compost.
Cover the pot with a clear polythene bag (not for bedding geraniums/pelargoniums) and place in a well-lit position out of direct sun.
Puncture the bag after rooting has taken place and keep the plants cool all winter.
Pot them up in spring and plant them out after the last frosts.
Don’t forget…
Tender bulbs. Many summer-flowering bulbs, such as acidanthera, galtonia, gladioli, ixia and tigridia, can be overwintered successfully outside provided you live in a mild area and your soil is well drained. Cut back the plants at the end of the growing season and cover the ground with an insulating mulch of manure or composted bark. If your soil is heavy and wet, borderline-hardy bulbs, corms and tubers are best lifted, dried and stored somewhere frost free. Towards the end of this month lift the cut back plants and dry them on mesh elevated on bricks or place in boxes in an airy shed or greenhouse. Clean the bulbs/corms/tubers once the stems fall away easily, then dust with flowers of sulphur to help prevent rotting. Store in boxes placed somewhere frost-free and airy. Check monthly for signs of deterioration and discard any suspect bulbs/corms/tubers.
Happy gardening!
