It may be December but if you look carefully, you could still spot a few of these still flowering. These big, blowsy tuberous begonias don’t like the cold, but in a sheltered position they can often defy the elements and keep on blooming when they should be tucked up indoors for the winter.
Their cousins, the fibrous-rooted begonias so popular because they provide months of non-stop flowers, have all but been turned to mush by the frosts. They should be thanked for their efforts and consigned to the compost bin. The tuberous varieties can be saved for next season, so don’t leave them outdoors any longer.
Basically, lift them and clean off as much soil as possible. Store them somewhere frost-free in trays of vermiculite or dry river sand. Keep checking them to make sure they are still healthy and sleeping peacefully and then, in late spring, awaken them.
Press them – hollow side up – into boxes of damp compost (it used to be peat, but in these eco days it pays to be a bit more pc) and move them somewhere where they can enjoy a temperature of between 60-70F.
When new leaves begin to appear, pot each tuber into individual 10-12.5cm (4-5ins) pots of John Innes No 2 compost or multipurpose compost.
The plants can then be allowed to get on with growing.
Harden them off before planting them outside after the danger of frost has passed (June is normally ideal).
The best position in sun or partial shade – with container-grown plants that should be no problem; just move the pot to get the best conditions.
In borders it’s a bit more difficult, but as long as the soil is fertile but well-drained, and the site gets a decent amount of sunshine, there should be no problem.
Water regularly during dry periods but avoid wetting the foliage.
Feed every week with a high-potassium feed such as Tomorite because these are flowers which grow big and which have big appetites.
Tuberous begonias can also be grown as houseplants. If you haven’t any tubers to lift and store, but fresh ones next spring and grow them as you would outdoor container-grown plants.
Begonias grown indoors can bloom virtually year-round, although they will require plenty of TLC – careful watering and feeding, shading from hot sun and even the occasional new container of compost.