If you’ve grown tender perennials this year, you need to overwinter them. Here’s a run-down of what to do with the most common half-hardy plants:
CANNAS: Lift after leaves have been frosted. Cut back stems to 5cm from the base. Store only undamaged fleshy rhizomes.
Remove loose soil, then store in trays of sand or vermiculite, with the crown of the plant just showing.
Keep just moist in a cold, frost-free greenhouse or conservatory. Container-grown plants can be stored in their pots after cutting back.
COBAEA SCANDENS (cup-and-saucer vine); Cardinal climber; Spanish Flag: These climbers must have a winter temperature of above 5ºC. Too dry, and they can fall prey to red spider mite.
DECIDUOUS AGAPANTHUS, GLOBE ARTICHOKES, LILIES: All benefit from a thick, dry mulch and good drainage when left in the ground – straw, compost, chipped bark or well-rotted manure are suitable.
BANANAS: Kept dry over winter, plants can remain dormant and will survive 5ºC - but won’t fruit. Plants are best overwintered at temperatures of around 10ºC in a heated greenhouse. For fruit, a winter minimum of 15ºC is recommended.
FIGS: My tree lives in a 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. As mine is in a light place, it will be wrapped in dark fabric to prevent it from breaking dormancy early.
Keep the soil almost completely dry - moist soil can rot the roots.
YUCCAS/CORDYLINES: Overwinter more tender species (usually red, purple or variegated forms) in a greenhouse providing minimum temperatures of 5°C. Keep on the dry side.
How to look after your bedding plants over winter.
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, so need some moisture.
Ventilation is important, to prevent against mould and rotting. They only need to be frost-free, although above 5ºC is best - if frost damages the stems, the plant will die.
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, so discard the old one and cut the dead foliage off.
Place them in single layers in cardboard boxes with newspaper in between and keep in a cool, dry spot at about 5ºC.
When 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. 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.