IN THE FALL
At this point in the growing season, you should still have at least another month or two of good looks if you have been feeding your begonias well. Unfortunately, this was a very tough season for mildew, so many begonias will have some by this time. Even if your begonia looks bad the tuber that is growing shouldn’t be affected. You can remove any mildewed foliage or wait for it to die back itself.
As the days get shorter and the nights get colder your tuberous begonias and your foliage rhizomatous begonias begin to send their energy down into a storage tuber. You can help them go dormant by gradually withholding water. Eventually all the foliage will fall off and you are left with a pot or space of soil that looks like empty dirt. You have a few options of what to do once your begonias have died back:
1. If you don’t need the pot, just leave the tubers in the pot, and place it somewhere it won’t get wet during the winter.
2. Dig out the whole clump of soil and store in a dry spot.
3. Dig up the tuber only (no soil) and dry it in a sunny spot. Then store it in shavings or peat moss in a bag or box.
IN THE SPRING
If you left your tubers in pots, they should begin to sprout from February to April depending on the variety. If you removed your tubers, replant them around February. Starting in early March, begin to water gently. Too much water can rot the tubers. After the plants are several inches high you can begin to fertilize, a 1/2 strength dose the first time is good. You can also begin to pinch back the tips to encourage the plants to branch out.