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Overwintering tender perennials
Safeguard your investments by helping plants through the winter
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 perennials:
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 frost-free greenhouse or conservatory. Container-grown plants can be stored in their pots after cutting back.
ECHIUM: E. pininana is a biennial/triennial. After keeping seven inside last winter (and falling victim to aphids) - the three outside in pots emerged best, with fleece bags over them. Four didn't flower this year, so two are planted in gritty soil next to the greenhouse, with the other two in pots. They'll survive odd nights down to -4ºC. Remove all dead/marked leaves and reduce watering.
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.
CUCAMELONS: Cucamelons are perennials and produce radish-like roots. As they 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.
BANANAS: Kept dry over winter, 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'm using a tomato house with the heated pad from my propagator to keep night temperatures up.
FIGS: Mine 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.
Trimmed geraniums (pelargoniums) brought into the conservatory.
From top, bananas in large tomato house in the conservatory, on a heated pad to keep them awake; red Cordyline; Yucca, cacti and Morning Glory Grandpa Otts.
Dahlia Bishop's Children.
Bedding plants
DAHLIAS/TUBEROUS BEGONIAS: 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, 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 newspaper in between and keep in a cool, dry spot at about 5ºC.
PELARGONIUMS (geraniums): If they're 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, 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.
Learn how to store gladioli corms.
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.