I leave my tuberous begonias in their pots, but turn the pots on their sides in winter so they stay dry. When they get started in the spring, I upright them and let them grow.
My question: How far under the surface should the tuber be, or should the tuber be right at the surface of the potting soil?
Beverly Unck, Sacramento
Tuberous begonias (Begonia tuberhybrida) are a favorite summer garden flower, according to UC Master Gardener Greg Ratliff. They provide 1- to 2-inch blossoms from summer to fall and plants may reach a foot or more in height.
In winter, the tubers go dormant. The Sunset Western Garden Book suggests covering the tubers with no more than a quarter-inch of soil mix. Planting the tubers evenly with the soil surface, exposing some of the tuber with the indented side up, is also correct.
It is important to note that planting them more than an inch deep could cause the tubers to rot from too much moisture.
Your other concern is proper storage for containerized tuberous begonias. It is suggested to leave the containers upright instead of on their sides, allowing the soil to dry completely.
If planted in the ground, lift tubers after the first frost, allowing some soil to cling to them. Let the tuber dry completely. Avoid tuber rot by removing the dried stems before winter storage. New eyes will form the next year's growth.
Replant the tubers in late winter after frost danger has past.
Generally, most begonias can be grown in the ground or in containers. They do best in well-drained, rich soil. They prefer filtered but bright light. For best flowering, fertilize twice a month during the growing season.
Tuberous begonias are among the showiest of this large family. Flower shapes include rose, carnation and camellia. They come in every color except blue and green.
Tuberous begonias also can provide a fantastic hanging-basket display. New tubers can be planted in late winter. Look for them in mail-order catalogs or nurseries.
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