Planting: You can start the begonia tubers indoors in March/April. Plant the tubers hollow side up, no more then half an inch below the soil level, with adequate drainage holes. If you're using commercial potting mix, mix it with equal parts of peat moss and sand or perlite.
the tubers once really well, to wake them up, and place them in a warm,
bright spot where the temperature will never fall below 60° F. Cover
the freshly planted tubers with paper or polythene to promote growth,
but remove the covering as soon as growth appears. Don't water again
until you see some growth or the soil is quite dry; the begonias don't
have any roots yet and you don't want to drown them. Some begonias will
sprout right away others will take weeks; generally, expect to see
growth shoots in five to six weeks.
Once They're Growing: Once
the shoots are showing, water regularly, never allowing the soil to dry
out. Give maximum light, but shade from direct sun. Applying liquid
plant food will improve your Begonias' growth; feed them with half
strength balanced fertilizer the first time when their leaves and stems
are about 3 inches tall, wait two weeks, and then start a regular
feeding schedule. When the shoots are 6 inches tall, the Begonias are
ready to be transplanted to the garden or outdoor containers. Don't put
them outdoors, though, until all danger of frost has passed.
Begonias thrive in partial to full shade and need well-drained soil.
They need to be kept away from hot sun and drying winds. As they
dislike dry conditions, they'll need to be watered generously,
especially during hot weather. Keep their soil moist but not soggy; the
tubers will rot if they get too much water. Always water the soil
around the plants rather than the plants themselves, if possible, to
avoid mildew, and at the first sign of a white patch on any of your
begonias' leaves, apply a fungicide right away. Feed Begonias with a
well-balanced plant food every 2 to 3 weeks.
the show is over in the fall, you'll be able to dig and store your
tubers until spring rolls round again. Because Begonias are prone to
rot if left in the ground until their tops fall off, I recommend
bringing them indoors before frost. If you place them in a well-
ventilated room and start withholding water, the foliage will die back
and you'll be able to remove the stems and leaves without damaging the
tubers. Clean them off, dust with soil dust, and cover the tubers with
dry sand, peat moss or vermiculite; store them in a cool,
well-ventilated, frost-free area such as a garage over winter. (55° F