Tuberous begonias (Begonia x tuberhybridas) produce some of the most exquisite flowers in the plant world. They come in a wide variety of colors, such as salmon, red, pink, white and orange; and sizes, from varieties with tiny one-half inch wide flowers to flowers as large as 13 inches in diameter. Whatever variety of tuberous begonia you want to grow, make sure you protect them from wind and plant them in well draining soil.
Start tuberous begonias indoors approximately one month before the last average spring frost date in your growing region, as suggested by the University of Vermont. Scoop a high quality potting mix that contains perlite and peat moss into individual 6-inch pots until each pot is approximately two-thirds full. Plant one begonia tuber into each 6-inch pot. Make sure you plant the begonia tubers so that the side with the depression is facing upward. Place a one-half inch layer of potting mix over the top of each begonia tuber.
Place each of the 6-inch pots in a dark place where they will receive lots of warmth--temperatures around 70 F are best. Keep the growing media just barely moist, never soggy wet. Water only when the soil starts to dry out.
Transfer the 6-inch pots to a light-filled location, such as near a sun-filled window, as soon as the begonia tubers sprout, which should be approximately one to two weeks, depending on conditions.
Place the pots containing the begonia tubers outside for a few hours each day to accustom them to exterior conditions. Do this once the begonias are about 2.5 to 3 inches tall, and there is no more frost expected; the outside temperature should be 55 F or above. Place the pots in a location which provides protection from wind, and where there is eight to nine hours of filtered light a day. Do this for about one week to 10 days before you transfer them outside for the season.
Transfer the begonias to a location outside in an area in your garden after you have acclimated them to outside conditions. Keep the begonias in the 6-inch pots. Put the tuberous begonias where they will receive morning sun and afternoon shade. Check on the tuberous begonias often--every day or every other day. Water the begonias as the soil starts to dry out. Do not overwater tuberous begonias, which can cause the tubers to rot.
Push in a slender one-quarter inch wide bamboo stake about 2 or 3 inches away from the stem of each tuberous begonia once the begonias are about 2 to 3 inches tall. Tie the stem of each tuberous begonia loosely to a bamboo stake using a figure eight pattern with gardeners twine. Tuberous begonias can grow to 18 inches tall and frequently need support.
Fertilize the tuberous begonia once a month using a water-soluble fertilizer, such as 10-10-10 or 20-20-20. Make sure to follow the directions provided by the manufacturer so you will know how much fertilizer to use.
Remove all faded begonia blossoms using a pair of scissors or small pruners. Cut the blossom off close to the stem. Removing faded blossoms can keep the begonias blooming and ensure vigorous growth.