How to Care for a Yellow Begonia

Yellow begonias are cultivars of hybrid tuberous begonia type (Begonia x tuberhybrida) developed for their yellow blooms. They grow in U.S. Department of Agriculture plant hardiness zones 9 through 11, typically growing between 1 and 1 1/2 feet tall. The flowers bloom from summer through early fall. Caring for yellow begonias the right way keeps these showy flowers blooming abundantly. A striking cultivar to try is 'Nonstop Mocca Yellow' (Begonia x tuberhybrida 'Mocca Yellow'), a hybrid cultivar with yellow flowers and deep purple leaves.

From spring through summer, water begonias when the top of the soil starts to look slightly dry. Each time you water, the soil should be damp 5 to 6 inches deep. Discontinue watering in early fall. This triggers yellow begonia bulbs to go dormant for the winter.

Start fertilizing in the spring with 5-1-1 fertilizer. Use 1 tablespoon mixed with 1 gallon of water per plant twice a month. In late spring and early summer, when flower buds start to form, add 1 tablespoon of 0-10-10 fertilizer every other week. Continue with the bi-monthly 5-1-1 fertilizer.

Yellow begonias are susceptible to sap-sucking insects like whitefiles and aphids. Given a chance, slugs and snails will also chew through the leaves and eat the flowers.

Check yellow begonias for aphids and whiteflies at least once a week. Aphids are small, soft-bodied insects, typically green or pale white. Whiteflies are fly- or moth-shaped pests with white wings. Use insecticidal soap spray to control aphids and white fly. Soap sprays typically come in a concentrated form. To make a 2 percent dilution, mix 4 teaspoons of soap concentrate with 1 quart of water in a spray bottle. Shake it to mix the two ingredients, then spray the insects directly.

Avoid spraying bees, ladybugs and other beneficial insects.

Spray yellow begonias on a windless day.

Avoid getting the soap spray on your skin or in your eyes.

Keep soap sprays and all other pesticides out of reach of children and pets. 

Check yellow begonias for slugs and snails. If you see holes in the leaves but can't spot the culprit, wait until dark, then take a flashlight out to the begonia bed. Pick them off and drown them in a bucket of water with a few squirts of dish soap.

Yellow tuberous begonias and other tuberous begonia cultivars are particularly susceptible to the fungal disease powdery mildew. Powdery mildew causes grey white splotches to appear on the leaves, stems and flowers. Treat the affected begonias with horticultural oil spray.

Clean 1 1/2 or larger gallon spray bottle 

Horticultural oil 

Tablespoon measure 

Baking soda 

Fill the spray bottle with 1 gallon of water.

Add 3 tablespoons of concentrated horticultural oil to the water.

Mix in 3 tablespoons of baking soda to the water-oil mix.

Fasten the lid securely and shake to mix the three ingredients.

Spray the areas of the yellow begonias that show symptoms of powdery mildew.

Only use horticultural oil sprays in weather below 90 degrees Fahrenheit.

Avoid getting the concentrated or mixed product in your eyes or on your skin.

Keep the concentrated and mixed product away from children.

Be careful to avoid spraying beneficial insects, such as bees, ladybugs and predatory garden spiders. 

Outside of USDA zones 9 through 11, where begonias left in the ground overwinter will die, you can preserve them by digging and storing the tubers. In the fall, before the first expected frost in the area, cut back any remaining top growth and dig up the tubers. Shake off the dirt and pack them in a bucket filled with dry media, such as peat, clean dry sand or sawdust. Keep the tubers in a cool, frost-free spot through the winter.