Begonia

About Begonia

Begonias are shade-garden favorites with waxy or showy leaves and flowers from spring to frost. Wax begonias are tough little bedding plants; tuberous begonias have big rose-like flowers for cool, shady spots; Rex begonias are grown for their painted leaves; and Dragon Wing types make arching 2-3 foot plants that bloom nonstop in sun or shade (Clemson). Bronze-leaved wax begonias handle more sun than green-leaved ones.

Grown as a summer annual in most of the US; wax begonias survive winter only in about zones 9-11 and Rex begonias in 10-12 (NC State). Tuberous begonias aren't hardy in the North; dig and store the tubers (UMN). UF/IFAS rates wax begonia 'caution - manage to prevent escape' in Florida (advisory).

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

• Start seeds indoors: 12 to 16 weeks before the last frost
• Set out plants: up to 2 weeks after the last frost

Sow the dust-fine wax begonia seed on the surface, uncovered, at 68-75 F about 12 weeks before planting out; tuberous begonia seed needs 14-16 weeks (Clemson). Start tuberous begonia tubers indoors 8-10 weeks before the last frost, hollow side up, about 1/2-1 inch deep at around 70 F; they flower 12-14 weeks after planting (Iowa State). Set plants out after frost, wax begonias 6-8 inches apart and other bedding kinds about 12 inches (Clemson). In fall, dig tuberous begonias when the leaves yellow or after the first frost, cure them dry, and store them in peat or vermiculite at 40-50 F (UMN); bring potted wax begonias indoors to a cool spot and water less (NC State).

Soil

Moist, well-drained soil rich in organic matter; wax begonias like fertile soil, and Rex begonias like slightly acid soil and hate wet feet (Clemson, NC State).

Work in organic matter for moist, well-drained soil; wax begonias like fertile soil (Clemson).

Feeding

• Tuberous begonias started indoors, once shoots appear: diluted balanced fertilizer. Feed with a dilute solution every 2-3 weeks while they grow indoors (Iowa State).
• Tuberous begonias, through the summer until the end of August: dilute balanced fertilizer. Tuberous begonias are fairly heavy feeders; feed lightly but regularly, then stop at the end of August so the tubers can go dormant (UMN).

Most begonias aren't heavy feeders; too much fertilizer or water makes tuberous begonias drop their buds (Clemson). Don't water when hot sun is on the leaves, and test insecticidal soap on a few leaves first, since begonias can be sensitive to it (Clemson).

Harvest

Wax and Dragon Wing begonias bloom from spring until frost and don't need deadheading; Dragon Wing is sterile, so it keeps reblooming (Clemson). Tuberous begonias bloom through summer; too much water or fertilizer makes them drop buds (Clemson, UMN).

Varieties (20)

Pests to watch for

Mealybugs, Twospotted spider mite, Thrips, Scale insects, Slugs, Brown garden snail

Diseases and problems

Gray mold (botrytis blight), Powdery mildew, Pythium root rot, Stem rot, Bacterial leaf spot, Impatiens necrotic spot virus, Tomato spotted wilt

In the kitchen

Safety: NC State lists begonias as poisonous with low severity: the roots hold the most calcium oxalate, which burns the mouth and throat if eaten. Rex begonia sap can irritate skin. Don't eat any part.

Pets: Toxic to dogs, cats and horses (ASPCA): soluble calcium oxalates cause drooling and vomiting in dogs and cats, the underground parts are the most toxic, and grazing animals have had kidney failure.