How to get tender plants through winter
If you grow exotics, overwintering tender perennials is an essential skill, or they’ll die during winter. Here’s what you need to know about the most commonly grown plants… Read more on this subject in my overwintering guide.
Overwintering tender perennials – Cannas
Lift canna plants after the leaves have been frosted. Cut back stems to 5cm from the base. Store only undamaged fleshy rhizomes – others may rot. Remove loose soil, then store in trays of sand or vermiculite, with the crown of the plant just showing. Keep just moist in a frost-free greenhouse or conservatory. Container-grown plants can be stored in their pots after cutting back. In spring, pot on rhizomes into fresh compost and increase watering. Harden off and only place outside after the last frosts. Feed regularly.
Echiums
Echium pininana is a biennial or triennial – some of mine have even gone on for a fourth year before flowering. It all depends on the outdoor conditions. After a trial during winter 2013/14, seven were kept in the conservatory in pots. They fell victim to aphids and didn’t flower the next year. However, three plants kept outside in pots under fleece bags emerged best and flowered. Five more spent that winter outside, in fleece, in gritty soil. They survived but looked very raggy. E. pininana will survive odd nights down to -5ºC. Extended cold snaps, such as early 2021’s run of -7ºC nights, will finish them off. Other varieties are much less frost-tolerant.
In spring, remove all dead and marked leaves. By late April, if there’s a healthy crown, plants will elongate, and the huge flower spikes will form. They’re monocarpic and will die afterwards, but will self-seed everywhere – I use a process of natural selection to let the toughest survive the winter and grow only from them.
Overwintering tender perennials – Climbers
Cobaea scandens (cup-and-saucer vine); Cardinal Climber; Spanish Flag, Canary Creeper: These exotic climbers must have a winter temperature of above 5ºC. Too dry, and they can fall prey to red spider mite or die. Quite tricky to get the balance right. I’ve only managed it with a cup-and-saucer vine. Very fast-growing, so maybe worth just treating them as annuals.
Agapanthus
The most tender Agapanthus are evergreen, but I keep my deciduous plants in a cold greenhouse during winter. In mild areas, you’ll get away with placing pots in a light, frost-free place, such as the bottom of a south- or west-facing wall. Wrap pots and plants in horticultural fleece from November to April. I keep mine pretty dry, and the foliage (deciduous) shrivels until the days lengthen and you can see new growth in March. By April, I repot if necessary and increase watering.
Overwintering tender perennials – Cucamelons
These odd little watermelon lookalikes, tasting of cucumber, are perennials. Instead of being grown from seed every year, you’ll get an earlier crop of cucamelons by overwintering their radish-like roots. As plants slow down in autumn, expose the roots to see if they have produced tubers. Store these in slightly moist compost in a frost-free place. Plant into pots early to mid-April under glass. Another one difficult to get the balance right – most of my tubers rotted. Have backup emergency seeds just in case.
Bananas
Kept dry over winter, banana plants can remain dormant and will survive 5ºC, but won’t fruit. Plants are best overwintered at temperatures of about 10ºC in a heated greenhouse. For fruit, a winter minimum of 15ºC is recommended. I use a heated pad from my propagator to keep night temperatures up. They continue to grow, but not at their usual phenomenal rate. If you’re doing this (because you want to enjoy the foliage), give them a touch more water, or they’ll lose their leaves. As the days lengthen, repot and increase watering.
Overwintering tender perennials – Figs
I once had an ’emo fig‘ as it sulked a lot and lived in the cold greenhouse. In autumn, reduce watering and remove any remaining leaves and fruit. It needs to be dark and dry, and just above freezing – an unheated shed or garage is ideal. The usual advice is to keep it dark. I didn’t bother. Keep the soil almost completely dry – moist soil can rot the roots. It did awaken, but sadly, it is no more.
Yuccas and Cordylines
There are hardy varieties out there but I’m talking about the more tender species (usually red, purple or variegated forms), or like mine, the houseplant type. Overwinter them in a greenhouse/conservatory/porch, providing minimum temperatures of 5°C. Keep on the dry side.
Potted guide: overwinter tender perennials
- Watch out for pests – you should thoroughly clean out your overwintering spots before moving plants into them, as there are bound to be some pests you miss.
- Place yellow sticky fly traps every 1m to catch any you miss and inspect plants at least twice a week.
Bedding plants
Dahlias and tuberous begonias
To overwinter tender perennials like dahlias and tuberous begonias, here’s what to do. When the dahlia foliage has been blackened by frost, cut off the flowering stems 5cm from the base and trim away thin roots. Use a fork to lift plants, taking care not to damage the tubers. Put soil-free tubers upside down in a cool place for a few weeks to dry. Bury in trays filled with dry sand, soil or compost, leaving only the flower stalks exposed. Place in a cool but frost-free place.
Gladioli
Wait until leaves have died back, then dig up the corms. Remove any loose dirt. Leave corms on top of the soil for two days, then transfer them to a box and place it in a warm, dry place with good air circulation, for two weeks. Gladioli form a new corm on top of last year’s old one, so discard the old one and cut the dead foliage off. Place them in single layers in cardboard boxes with newspapers in between and keep them in a cool, dry spot at about 5ºC.
Pelargoniums (geraniums)
If Pelargoniums are warm enough and in good light, they will continue to grow and flower. Mine generally do until November, then I reduce watering. Before bringing them under glass, clean off dead leaves or dying flowers and check for hidden pests. Try to keep the atmosphere dry, but not the roots – the plants do not go into dormancy and need some moisture.
Ventilation is important to prevent mould and rotting. They only need to be frost-free, although above 5ºC is best – if frost damages the stems, the plant will die. For more on choosing plants, visit my plant categories.
