Begonias (Begonia spp.) are reliable, nearly continuous-blooming bedding and container plants for shade and part shade, filling in spots too dim for most other flowering annuals to perform well. Wax begonias and tuberous begonias are the two types most commonly grown as bedding plants, the first valued for its tidy habit and nonstop small flowers, the second for larger, showier blooms on a slightly more upright plant. Even between flushes of bloom, the glossy, often reddish-tinged foliage carries its own visual weight, which is part of why begonias read as attractive all season rather than only while flowering. In Kentucky's zone 6b, begonias have no winter hardiness outdoors and are grown as tender annuals, planted out only once the soil and nights have genuinely warmed. They're an easy, forgiving choice for shaded beds, window boxes, and porch containers.
Sowing and planting
Wax begonias can be started from seed indoors, but the seed is dust-fine and slow to germinate, so most home gardeners buy started bedding packs instead of sowing their own. Tuberous begonias are usually started from dormant tubers, pressed hollow-side-up into shallow trays of moist potting mix indoors in late winter, about 8 to 10 weeks before your last frost date, then grown on in bright, indirect light until it's warm enough to plant out. Begonias resent being set outside before the soil and nights have properly warmed, so hold off until temperatures are reliably mild; in zone 6b that generally means late May, once the last frost date has safely passed and nighttime lows have settled. Choose a part-shade spot, whether that's dappled light under trees, the east side of a building, or a bed that gets morning sun and afternoon shade, and space plants about 10 inches (25 cm) apart. Work some compost into the planting area beforehand, since begonias do best in soil that holds moisture without staying wet, and water well after planting to settle the roots.
Growing on
Keep the soil evenly moist through the growing season rather than letting it swing between bone-dry and saturated; begonias respond poorly to both extremes, and soggy soil in particular invites root and stem rot. A couple of inches of mulch over the root zone helps even out soil moisture and keeps roots cooler through summer heat. Feed lightly with a balanced, diluted fertilizer every few weeks during the growing season, since begonias are modest feeders and heavy fertilizing tends to push soft, floppy growth rather than better flowering. Tuberous begonias with large, heavy flowers sometimes benefit from a short stake or a bit of support, especially in a windy spot, but wax begonias are self-supporting and need none. Pinch back leggy stems on either type to encourage bushier growth, and keep an eye out for any damaged or discolored leaves, which are worth removing promptly since begonia foliage can be slow to self-clean.
Harvesting
Tuberous begonias, with their larger, more substantial blooms, make reasonably good cut flowers for a short indoor arrangement, while the smaller flowers of wax begonias are more often left on the plant than cut. Either way, deadheading spent flowers and removing any fading or damaged foliage as you go keeps plants looking tidy and encourages the next flush of bloom, since a begonia that isn't putting energy into fading flowers and seed pods puts it into new buds instead. As fall approaches and frost threatens, your end-of-season plan depends on which type you're growing. Wax and other fibrous-rooted begonias are typically treated as fully disposable annuals in Kentucky; once frost kills the top growth, simply pull and compost the plants. Tuberous begonias are worth saving: once frost blackens the foliage, cut the stems back, lift the tubers carefully from the soil, let them air-dry for a few days, and store them in dry peat moss or vermiculite somewhere cool and frost-free over winter, much the way you'd store a dahlia tuber, then start them again indoors the following late winter.
Problems and pests
White, powdery coating on leaves
Powdery mildew shows up as a dusty white film on leaves and stems, especially where air circulation is poor or plants are crowded. Space plants to allow airflow, avoid wetting the foliage when you water, and remove badly affected leaves; a fungicide labeled for powdery mildew can help on a bad outbreak, but better spacing usually prevents the problem in the first place.
Flowers and stems turning soft and gray
Botrytis blight (gray mold) develops on begonia flowers and stems during cool, damp stretches, leaving fuzzy gray growth on tissue that quickly turns to mush. Remove affected flowers and leaves promptly, water at the soil line rather than overhead, and thin crowded plantings to improve air movement around the foliage.
Ragged holes chewed in leaves overnight
Slugs and snails feed on begonia foliage after dark, leaving irregular holes and silvery slime trails behind, and they're especially drawn to the moist, shady conditions begonias prefer. Hand-pick at night with a flashlight, set out shallow dishes of beer as traps, or use iron phosphate bait around the bed, which is safe around pets and other wildlife.
Wilting plants with mushy, discolored stems at the soil line
Stem rot and root rot set in when soil stays too wet for too long, often from overwatering or poor drainage, and once a stem has gone soft and dark at the base there's usually no saving that plant. Let soil dry slightly between waterings, improve drainage in the bed or container, and remove and discard any affected plants before the rot spreads to their neighbors.
Sticky residue and distorted new growth
Mealybugs cluster in leaf joints and on new growth, covered in a white, cottony coating, and leave behind a sticky honeydew that attracts sooty mold. Wipe off light infestations with a cotton swab dipped in rubbing alcohol, and treat heavier ones with insecticidal soap, checking plants again every week or two until the pests are gone.
Varieties worth growing
- Dragon Wing series – A vigorous, fibrous-rooted type with glossy, wing-shaped leaves and pendulous red or pink flowers, larger and more floriferous than typical wax begonias.
- Whopper series – A large, heat-tolerant wax begonia bred for bigger leaves and flowers than older bedding types, holding up well in brighter conditions.
- Nonstop series – A compact, upright tuberous begonia with large, rose-like double flowers in a wide color range, a dependable choice for containers and shaded beds alike.
- Illumination series – A trailing tuberous begonia well suited to hanging baskets, with cascading stems and abundant double blooms.
- Big series – A large, mounding wax begonia with bronze or green foliage, useful where you want more bulk and presence than smaller bedding types provide.