The same pot of tuberous begonias came back for a third summer on my shaded back porch, big orange blooms and all. I had pulled the tubers each fall and kept them cool and dry through winter. The first year I tried this, I left a batch of them outside one October night. Frost turned the leaves black and the tubers to mush by morning.
How you overwinter begonias depends on which type you grow. Tuberous begonias go dormant and need a cool, dry rest. Fibrous and cane types, like wax begonias and angel wings, can keep growing as houseplants all winter long. Sort your plants by type first, because the wrong method kills the wrong begonia. If you are not sure what you have, check whether the plant grows from a round, flat tuber or from a fibrous mat of roots.
Tuberous types enter begonia dormancy no matter how you grow them. As your days get short and cool, the plant pulls its energy back into the tuber and the top growth dies off. This rest is not optional. The tuber needs a cool winter break to store up energy and bloom again next season. Skip the rest and you get weak, leggy growth or no flowers at all. When you understand this, your storage choices start to make sense. You are not killing the plant by letting it go dormant. You are giving it the rest it would get in the wild.
For storing begonia tubers, wait until frost blackens the foliage. Then lift the tubers from your soil with a fork and shake off the loose dirt. Do not wash them, since water invites rot. Let them dry for a few days in a sheltered spot, then trim off the dead stems. You want the skin to feel firm and papery before you pack anything away.
Once frost kills the top growth, dig up the tubers and brush off loose soil by hand. Leave them unwashed so they stay dry.
Set the tubers in a dry, airy spot for about a week until the skin firms up and the old stems pull away clean.
Nest the tubers in dry peat moss or vermiculite inside a perforated bag, then keep them at 40 to 55°F (4 to 13°C).
Good begonia winter care means you pick a storage spot that stays cool but never freezes. An unheated basement, a cool closet, or a garage that holds above freezing all work well for you. Check your tubers once a month through the winter. Toss any that feel soft or smell off before the rot spreads to the rest of your batch. A flashlight and a quick squeeze tell you all you need to know. This monthly check is the small habit that lets you overwinter begonias with almost no losses.
Fibrous and cane begonias let you skip the storage step. Bring them indoors before your nights drop below 55°F (13°C), since cold air shocks these tender plants fast. Set them by a bright window out of direct sun and cut back on your watering. They slow down in winter, so soggy soil will rot the roots. Give them a little less of everything and they coast through until spring. If you see leaf drop at first, do not panic, since the plant is just adjusting to your indoor light.
Start your stored tubers again about 6 to 8 weeks before your last spring frost. Set them hollow side up in a tray of damp potting mix and keep them around 70°F (21°C) to wake them up. Once you see shoots and roots appear, pot them on and grow them indoors until the nights stay warm. Then move them back outside for another summer of bloom. Do this each year and your tubers will keep getting bigger and flower harder, the way that porch pot did for three summers straight.
Read the full article: Begonias Plants: Full Care Guide
