IF you’ve grown tender perennial plants this year, now’s the time to decide whether to overwinter them or not.
To me, it’s a no-brainer – why let perfectly good plants die and waste your money?
Here’s a run-down of the most common half-hardy perennials to keep, plus a few I’m experimenting with.
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, as this can lead to rotting. 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.
CANNAS: Like dahlias, lift after the 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.
RICINUS (castor oil plant): Usually grown as an annual. This year, I’m cutting them back and moving them into the conservatory - they’re in big pots with geraniums.
ECHIUM: E. pininana is a biennial/triennial. I have 10 in pots, seven of which are inside - the other three are taking their chances outside. They’ll survive odd nights down to -4ºC. Remove all dead/marked leaves and reduce watering.
COBAEA SCANDENS (cup-and-saucer vine): This half-hardy perennial climber from Mexico is in a massive ceramic pot and must have a winter temperature of above 5ºC. Too dry, and it can fall prey to red spider mite.
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, at about 29ºC, for two weeks.
Gladiolus forms a new corm on top of last year’s old one, so discard the old one, 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.
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.