Begonia Care: How to Keep Yours Blooming Outdoors
Everything you need to keep outdoor Begonia × tuberhybrida and wax begonias blooming from transplant to frost — sun tolerance, watering, tuber storage, and disease prevention.
Which begonia are you growing?
The name "begonia" covers several hundred species and hybrids, but three types dominate North American home gardens. Identifying which you have changes the care advice significantly.
Tuberous begonias (Begonia × tuberhybrida)
These are the showiest — large double or single blooms in white, yellow, orange, pink, red, and bicolors, on plants 12–18 inches tall. They grow from fleshy tubers and go fully dormant in winter. Per University of Minnesota Extension, tuberous begonias "prefer cool summer temperatures" and perform poorly when heat stays above 90°F for extended periods. They are best suited to gardens in the Pacific Northwest, northern tier states, and coastal areas with moderate summers.
Wax begonias (Begonia semperflorens)
Compact mounding plants, 6–12 inches, with glossy leaves and small single flowers. The most commonly sold bedding begonia at every big-box garden center. More heat-tolerant than tuberous types and far more forgiving of irregular watering. Per Clemson Extension HGIC, wax begonias "thrive in hot, humid summer weather" as long as drainage is adequate, which sets them apart from tuberous types.
Rex begonias (Begonia rex hybrids)
Grown primarily for dramatic foliage — swirling silver, burgundy, and green patterns — rather than flowers. These are the most shade-tolerant of the three and the least heat-tolerant. Most gardeners treat them as container plants moved outdoors in summer; they don't perform well in ground beds in hot climates.
USDA hardiness and where begonias grow
Tuberous begonias are perennial only in USDA zones 9–11, where tubers survive winter in the ground. In zones 3–8, they are grown as annuals with tubers dug and stored over winter. Wax begonias are treated as annuals in all zones below 10. Per Clemson Extension HGIC, both types are "tender perennials grown as annuals in most of the United States."
Most growers in the mid-Atlantic, Midwest, and Northeast start begonias as transplants — either purchased or started from tubers indoors — rather than direct sowing, because begonia seeds are extremely fine and germination is slow.
Light
Light requirements differ between the two main types, and this is where most placement mistakes happen.
Wax begonias tolerate a wider range than people expect. The bronze-leafed varieties handle more direct sun than the green-leafed ones. Per Clemson Extension HGIC, "bronze-leafed varieties grow well in full sun to light shade" while "green-leafed varieties prefer partial shade." In zone 7+ gardens, afternoon shade for all wax begonias avoids bleaching and heat stress.
Tuberous begonias are shade lovers. They bloom best in bright indirect light or dappled morning sun with solid afternoon shade. Full sun scorches the petals of the large-flowered types and causes premature bud drop. North-facing beds or the shade of a high-canopy tree are their sweet spot. Most growers find that a spot with two to three hours of morning sun and bright shade the rest of the day produces the strongest bloom display.
Watering
Overwatering is the most common cause of begonia failure. Both types are susceptible to root rot in waterlogged soil, and the symptoms — yellowing lower leaves, soft stems at the soil line — can look deceptively similar to drought stress.
The standard approach: water when the top half-inch of soil feels dry to the touch, then water thoroughly until drainage exits the pot or the bed soil is wet to 6 inches. Do not water again until the surface has partially dried. Per University of Minnesota Extension, tuberous begonias "require consistent moisture but must never sit in wet soil."
Water at the base of the plant, not from above. Wet foliage stays wet in shaded conditions and creates ideal conditions for Botrytis cinerea (gray mold), which is the most serious disease problem in begonias. Morning watering, if overhead, gives foliage time to dry before evening; evening overhead watering in humid weather is asking for trouble.
Container begonias dry out faster than in-ground plants — in hot weather, daily watering may be necessary. Self-watering containers with reservoirs work well for tuberous begonias in particular, as they buffer against the boom-bust watering cycle that stresses these plants.
Soil and pH
Begonias prefer a loose, well-draining, moderately fertile soil with a slightly acidic pH. Per Clemson Extension HGIC, a target pH of 5.5–6.5 is ideal. Heavy clay soils that retain water are the enemy of begonias — if your soil doesn't drain well, raised beds or containers filled with a quality potting mix produce far better results than amending in-ground clay.
For in-ground beds, working 2–3 inches of compost into the top 8 inches of soil before planting improves both drainage and fertility. Avoid high-phosphorus "bloom booster" fertilizers at planting time; excessive phosphorus can lock out micronutrients in acidic soils.
Planting
Timing is critical. Begonias are cold-sensitive and should not go into the ground until soil temperatures are reliably above 60°F and nighttime temperatures stay above 50°F. In zone 7a Long Island, this generally means late May. Planting too early produces stunted plants that never fully recover their growth momentum.
For tuberous begonias started from tubers: place tubers hollow-side up, barely covered with soil or potting mix, in a warm (65–70°F) location indoors 8 weeks before the last frost date. Per University of Minnesota Extension, tubers should be started in late February or March for northern zones. Transplant outdoors after hardening off for 7–10 days.
Spacing: wax begonias, 6–8 inches apart for a solid look; 10–12 inches for more open beds. Tuberous begonias, 12–15 inches apart — they need air circulation. Set transplants at the same depth they were growing in their nursery container; burying the crown invites stem rot.
Fertilizing
Begonias benefit from regular feeding through the growing season. A water-soluble balanced fertilizer (10-10-10 or similar) applied every two to three weeks keeps wax begonias blooming heavily. Tuberous begonias respond well to a fertilizer with a slightly higher potassium ratio once they begin setting buds — potassium supports flower production and stem strength.
Per Clemson Extension HGIC, "a slow-release fertilizer mixed into the soil at planting time can reduce the need for supplemental feeding," though for heavy-blooming tuberous varieties in containers, supplemental liquid feeding is still recommended through mid-summer.
Reduce feeding in late summer. For tuberous begonias being overwintered, stop fertilizing about 6 weeks before the expected first frost to let the tubers harden off properly.
Tuber storage (tuberous begonias only)
In zones below 9, tuberous begonia tubers must be dug and stored indoors before hard frost. Let the first light frost kill back the foliage (or cut plants back to 2–3 inches), then carefully dig tubers before a killing frost. Per University of Minnesota Extension, allow tubers to dry for several days in a warm, dry location, then store in barely moist peat moss, vermiculite, or sawdust at 45–55°F over winter. Check monthly for rot — a soft, dark spot can spread to the whole tuber if not caught early. Cut away any rotted tissue and dust with sulfur before returning to storage.
Healthy stored tubers can be started again in spring and will produce larger plants than first-year tubers — many long-time begonia growers have tubers 10 or more years old that produce spectacular, dinner-plate-sized blooms.
Common problems
Botrytis blight (gray mold)
The most damaging disease of outdoor begonias in humid conditions. Caused by Botrytis cinerea, it appears as gray, fuzzy growth on flowers, buds, and stems, usually starting with spent blossoms that weren't removed. Per UC IPM, management relies on improving air circulation, removing spent flowers immediately, avoiding overhead watering, and applying a copper-based or chlorothalonil fungicide at first sign. Remove and dispose of infected plant material — do not compost it.
Powdery mildew
White powdery coating on leaves, most common in late summer when nights cool and humidity rises. Tuberous begonias in crowded plantings with poor air circulation are most susceptible. Per UC IPM, sulfur-based fungicides applied preventively and improving plant spacing reduces incidence.
Stem rot and root rot
Caused by Pythium and Rhizoctonia species in waterlogged soils. Stems become soft and brown at the soil line; plants wilt even with moist soil. There is no cure once rot has reached the crown — remove affected plants. Prevention is improving drainage and not overwatering.
Mealybugs and thrips
Mealybugs appear as white cottony masses in leaf axils and stem joints. Thrips cause silvery streaking on petals and leaf distortion. Per UC IPM, insecticidal soap or neem oil applied to the undersides of leaves provides control for both pests. Remove heavily infested plant parts before treating.
Frequently asked
Why are my begonia leaves turning yellow?
Yellowing lower leaves on begonias most often indicate overwatering or root rot. Check the soil — if it's wet and the pot or bed has poor drainage, let it dry out and improve drainage before the next watering. If the soil seems appropriately moist, check for mealybugs, which cause yellowing as they feed. Nutrient deficiency (particularly iron) can cause interveinal yellowing in overly alkaline soils, but this is less common than water-related causes.
Why are my begonias not blooming?
The most common reasons: too much shade for wax begonias (they need some direct light), excessive nitrogen fertilizer (promotes leaves over flowers), or planting too early into cold soil that stunted root development. Tuberous begonias that haven't been fed with adequate potassium once budding begins may produce fewer blooms. Per University of Minnesota Extension, "plants that are heat-stressed often drop buds" — prolonged temperatures above 90°F can shut down blooming in tuberous types until it cools.
Can I overwinter wax begonias?
Yes, though it's labor-intensive. Most growers find it easier to buy new transplants each spring. If you want to try, take 4-inch stem cuttings in early September, root them in water or moist perlite indoors, and grow them as houseplants under bright grow lights through winter. Plants can be moved back outdoors after frost danger passes the following spring.
When do I dig tuberous begonia tubers?
After the first light frost kills the foliage, or when night temperatures consistently drop below 50°F. Don't wait for a hard freeze — frozen tubers do not store. Dig carefully with a trowel, keeping as much root intact as possible, and allow tubers to cure (dry) for 3–5 days in a warm, airy spot before packing for storage.
Are begonias deer-resistant?
Begonias have some deer resistance due to their bitter sap, but "deer-resistant" is never an absolute claim in high-pressure areas. In areas with moderate deer pressure, most growers find begonias are left largely alone. Where deer pressure is severe, a repellent rotation is still advisable.