Tuberous Begonia Page
I've recieved many requests from begonia growers asking what to do with their tuberous begonias for the winter. I figured it would simplify things if I just gave you a page of the information.
Tuberous begonias have a winter dormant period that is determined by the day length and in cold climates, by the weather. This dormancy is a normal part of the life cycle of the tuberous begonia. Many people inquired whether they could be brought indoors and grown on through the winter. The answer is that it is possible with perfect conditions but the best course is to just let them follow their natural cycle and restart them next year. The following are the steps for storage. The time to ready your tuberous begonias for storage depends on what climate you live in so I'm going to give you both.
Northern/Cold climates: In areas that freeze during the winter, tuberous begonias must be dug up and the tubers stored indoors for the winter. The time to do this is after you've had that first light frost that ruins the foliage. This is a type of forced dormancy by the weather. A light frost won't damage the tuber under the ground but a hard one will.
Southern/Warm climates: In areas that don't have frost or rarely have frost, tuberous begonias go dormant on their own according to the day length. They usually reach that point in October or November. When they start turning yellow and dropping leaves and stems you need to stop watering.
2. What to do:
Northern/Cold climates: In cold climates, after the foliage has been ruined by the first light frost, dig up the entire plant with its tuber. Gently remove all the soil from the tuber and any loose roots. Check for pests or for rotted areas. Rotted areas can be removed with a sharp knife and dusted with a fungal powder. Lay the entire plant in a warm dry area for several days to thoroughly dry the tuber. Make sure to bring them indoors at night if it's going to freeze. Once the tuber is dry the stem/stems should detach easily. If they don't, it isn't dry enough yet, wait a while longer. (don't be overly concerned if you broke the tops off while digging or by accident, they should still be fine, it's just better if they come off naturally because there will be less chance of rotting.)
Southern/Warm Climates: In warm areas your main worry is keeping the tubers dry during the winter. If you are growing them in the ground it will be difficult to stop them from being watered by rain so you will need to follow the directions for northern climates and dig the tubers to store them. If you are growing them in pots, however, all you need to do is put the pots where they won't get wet or turn them on their sides so they can't be watered.
3. How to Store:
Northern/Cold Climates: Once your tubers are thoroughly dry, place each tuber into a separate paper bag and place the bags into a cardboard box for storage. The reason for the individual bags is so that pests or disease can't spread easily to the entire collection and because they will allow the tubers to breathe. Keep the box in a dark, dry, cool place for the winter (cool, not cold, slightly below room temp). Check the tubers periodically to make sure none are rotting and that no pests have gotten into them. Again rotted spots can be removed and the tuber redried and dusted if they aren't too bad.
Southern/Warm Climates: Like stated above, if they are in pots they can be stored right in the pots by either tipping the pots on their sides or storing them in a cool, dry, dark area where they won't get wet. Follow the cold area directions for tubers that are dug out of beds.
SOIL PREPARATION: Tuberous begonias can survive in many types of soils. The most important factor to be considered in preparing any soil for begonia is PERFECT DRAINAGE. A good potting mixture would consist of four parts well decayed mulch (leaf mold or forest humus), one part garden loam, and one part coarse sand. If these components are not available you can purchase a good "potting soil" from your local nursery. The mixture should contain humus, and it should be well drained. Do not use "planting mix". For outdoor beds it is a simple matter to prepare the average garden soil for tuberous begonias. If you have a heavy clay-type soil which drains poorly, add humus, sand, or both. If your soil is very light or sandy, add leaf mold, peat moss, or some other organic materials. If manure is used, it should be mixed into the soil well in advance of planting time. Fresh manure is not advisable. Large amounts of peat moss are not recommended except in very sandy soils or when used with sand in the mixture. Also you can use "planting mix" or fortified humus to prepare your outdoor beds.
STARTING TUBERS: It is very important that a SPROUT APPEARS before the tuber is planted. If your tubers seem slow to sprout, move them from the cool storage area to a warm dark place. When sprouts appear, the tubers are ready to be planted.
STEP I—Fill a nursery flat or similar shallow container with the planting medium, well rotted leaf mold is recommended. However, there are many satisfactory substitutes. The planting medium should be loose, well drained and it should not contain fertilizer or manure.
STEP 11—Space the sprouted tubers evenly in the flat—allowing four to six inches between tubers for root development. Bury the tubers—it is ESSENTIAL TO GOOD DEVELOPMENT THAT TUBERS ARE COMPLETELY COVERED AS THE ROOTS DEVELOP FROM THE TOP AND SIDES OF THE TUBERS.
STEP 111—Water carefully. The flat should be lightly but thoroughly watered so that the medium is uniformly moist. DO NOT OVER WATER Do not allow the planting medium to become wet and soggy at any time.
STEP IV—Place the planted flat in a warm place where it receives filtered sunlight. A temperature of 60-70 degrees is ideal. The flat should not be watered again until the surface of the soil begins to show dryness. As the plants develop, they will need water more often and in increasing amounts. It is important to keep the tubers in the flat until the roots are well developed. When the plants have made four or five inches growth and the root mass is well developed, they should be transplanted. Do not allow the plants to become crowded or spindly in the flat.
Link to more detailed tuberous page with photos