Learn About Begonias

How to Sow

Begonia may be grown from seed sown early indoors and transplanted outside after frost, started from potted plants in the garden, or started from tubers inside early or outside after frost.

Sowing Seed Indoors:

  • Fibrous rooted begonias may be started indoors 3 months before the last frost using a seed starting kit.
  • Sow very shallowly in seed starting formula as seeds need light to germinate well.
  • Keep the soil moist at 70-75 degrees. Begonias can benefit with bottom heat.
  • Seedlings emerge in 15-21 days.
  • As soon as seedlings emerge, provide plenty of light on a sunny windowsill or grow seedlings 3-4 inches beneath fluorescent plant lights turned on 16 hours per day, off for 8 hours at night. Raise the lights as the plants grow taller. Incandescent bulbs will not work for this process because they will get too hot. Most plants require a dark period to grow, do not leave lights on for 24 hours.
  • Thin to one seedling per cell when they have two sets of leaves. Seeds are tiny but plants grow quickly.
  • Seedlings do not need much fertilizer, feed when they are 3-4 weeks old using a starter solution (half strength of a complete indoor houseplant food) according to manufacturer’s directions.
  • For a more bushy plant pinch the top of the plant off when it has 6-8 leaves.
  • Transplant hardened-off seedlings to the garden after all danger of frost.
  • Before planting in the garden, seedling plants need to be “hardened off”. Accustom young plants to outdoor conditions by moving them to a sheltered place outside for a week. Be sure to protect them from wind and hot sun at first. If frost threatens at night, cover or bring containers indoors, then take them out again in the morning.  This hardening off process toughens the plant’s cell structure and reduces transplant shock and scalding.

Starting Begonias From Tubers:

  • For tuberous begonias, insert thin stakes next to tall cultivars at planting time, and use yarn to tie the stems loosely to the stakes as they grow as the brittle stems break easily.
  • Since tuberous begonias can take 3 months to produce a flower you may wish to start them inside and set them outside after all danger of frost.
  • Set tubers cup side up in shallow 6 inch pots filled with potting soil. Cover each tuber with one inch of potting soil.
  • Keep soil barely moist ant 70-75 degrees. Do not overwater.
  • To produce larger but fewer flowers, pinch off all but a few young stems.
  • Before planting in the garden, plants need to be “hardened off”. Accustom plants to outdoor conditions by moving them to a sheltered place outside for a week. Be sure to protect them from wind and hot sun at first. If frost threatens at night, cover or bring containers indoors, then take them out again in the morning.  This hardening off process toughens the plant’s cell structure and reduces transplant shock and scalding.

Planting Potted Plants in the Garden:

  • Select a location in full to part shade with good rich moist organic soil.
  • Prepare the bed by turning the soil under to a depth of 8 inches. Level with a rake to remove clumps of grass and stones.
  • Most plants respond well to soils amended with organic matter. Compost is a wonderful form of organic matter with a good balance of nutrients and an ideal pH level, it can be added to your planting area at any time. If compost is not available, top dress the soil after planting with 1-2 inches of organic mulch, which will begin to breakdown into compost. After the growing season, a soil test will indicate what soil amendments are needed for the following season.
  • Plants should stand 12 inches apart in the garden.
  • Dig a hole for each plant large enough to amply accommodate the root ball.
  • Set level with the surrounding soil. Fill with soil to the top of the root ball. Press soil down firmly with your hand leaving a slight depression around the plant to hold water.
  • Water thoroughly, so that a puddle forms in the saucer you have created. This settles the plants in, drives out air pockets and results in good root-to-soil contact.
  • Use the plant tag as a location marker.
  • Water thoroughly, so that a puddle forms in the saucer you have created. This settles the plants in, drives out air pockets and results in good root-to-soil contact.
  • If you live in a warm area tuberous begonias may be planted directly in the soil. Plant the tubers cup side up 12 inches apart and one inch deep.
  • Stake large tuberous begonia at the time of planting to avoid root damage.

How to Grow

  • Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their seeds from germinating. 
  • Mulches also help retain soil moisture and maintain even soil temperatures. For annuals an organic mulch of shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time. Always keep mulches off a plant’s stems to prevent possible rot.
  • Keep plants moist but not wet during the growing season, especially during dry spells. Plants need about 1 inch of rain per week during the growing season. Use a rain gauge to check to see if you need to add water. It's best to water with a drip or trickle system that delivers water at low pressure at the soil level. If you water with overhead sprinklers, water early in the day so the foliage has time to dry off before evening, to minimize disease problems. For tuberous begonias try not to wet the leaves and flowers. Keep the soil moist but not saturated. Do not over water fibrous begonia
  • Until plants become established, some protection from extreme winds and direct, hot sunlight may be necessary. Good air movement is also important.
  • After new growth appears, a light fertilizer may be applied. Keep granular fertilizers away from the plant crown and foliage to avoid burn injury. Use low rates of a slow release fertilizer, as higher rates may encourage root rots.
  • Deadhead throughout the season.
  • Monitor for pests and diseases. Check with your local Cooperative Extension Service for pest controls recommended for your area.
  • Remove plants after they are killed by frost in fall to avoid disease issues the following year.
  • Dig up tuberous begonia tubers just before the first frost. Cut back the stems and foliage and remove excess soil from the tubers. Dry them in a protected, shady, well ventilated spot, and store in boxes or shallow trays in a cool and dry location over the winter.

Growing tips

  • Use fibrous rooted begonias in containers and as edgings, as miniature temporary hedges, or in shade gardens to add summer-long color. They make a great cover over daffodils and other spring bulbs as well.
  • Once planted, fibrous begonias need almost no care beyond watering during dry weather.
  • Combine tuberous begonias in containers with other shade loving plants, in the ground they are lovely with ferns and other shade loving perennials. Keep them from walkways as the stems are brittle and easily broken.

Common Pests and Problems

Common Disease Problems

Bacterial Leaf Spot: First signs are small translucent spots with a broad yellowish edge that slowly enlarge and become angular or irregularly circular with a reddish center. It thrives in cooler temperatures. The disease may also affect and disfigure flower heads.Burpee Recommends: Remove infected plants. Avoid overhead watering. Do not work around plants when they are wet.

Black Rot: This bacterial disease thrives in warm and humid conditions and attacks the leaves. Yellow-orange V shaped lesions occur on the edges of the leaves and eventually dry out and the leaves fall off. Burpee Recommends: Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet. Control weeds where the disease can overwinter.

Botrytis: This fungus causes a grey mold on flowers, leaves, stems and buds. It thrives in cool wet weather conditions. Burpee Recommends: Remove affected plant parts, avoid watering at night and getting water on the plant when watering. Make sure plants have good air circulation. Contact your Cooperative Extension Service for fungicide recommendations.

Damping Off: This is one of the most common problems when starting plants from seed. The seedling emerges and appears healthy; then it suddenly wilts and dies for no obvious reason. Damping off is caused by a fungus that is active when there is abundant moisture and soils and air temperatures are above 68 degrees F. Typically, this indicates that the soil is too wet or contains high amounts of nitrogen fertilizer. Burpee Recommends: Keep seedlings moist but do not overwater; avoid over-fertilizing your seedlings; thin out seedlings to avoid overcrowding; make sure the plants are getting good air circulation; if you plant in containers, thoroughly wash them in soapy water and rinse in a ten per cent bleach solution after use.

Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.

Common Pest and Cultural Problems

Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.

Flower Drop: Flowers and flower buds suddenly drop off, no disease or insect is present. Burpee Recommends: Tuberous begonias are very sensitive to over fertilizing and too much water. Use a slow release organic fertilizer and do not over fertilize. Keep the soil barely moist but never wet. Begonias cannot take any frost, so make sure plants are protected from frost and freezing temperatures.

Mealybugs: Mealybugs are 1/8 to ¼ inch long flat wingless insects that secrete a white powder that forms a waxy shell that protects them. They form cottony looking masses on stems, branches and leaves. They suck the juices from leaves and stems and cause weak growth. They also attract ants with the honeydew they excrete, and the honeydew can grow a black sooty mold on it as well. Burpee Recommends: Wash infected plant parts under the faucet and try to rub the bugs off. They may also be controlled by predator insects such as lacewings, ladybugs and parasitic wasps. Check with your Cooperative Extension Service for pesticide recommendations.

Sunscald: Leaves are bleached and faded, often turn white with brown crispy edges. There are no signs of pests and diseases. Plants were usually recently moved. The bright light and heat from the sun break down the chlorophyll which leads to death of the leaf. Burpee Recommends: Transplant begonias to a spot that has more shade in the afternoon. Do not place begonias in a south or south-west exposure.

Thrips: Thrips are tiny needle-thin insects that are black or straw colored. They suck the juices of plants and attack flower petals, leaves and stems. The plant will have a stippling, discolored flecking or silvering of the leaf surface. Thrips can spread many diseases from plant to plant. Burpee Recommends: Many thrips may be repelled by sheets of aluminum foil spread between rows of plants. Remove weeds from the bed and remove debris from the bed after frost. Check with your Cooperative Extension Service for pest controls.

FAQ

Do you carry Wax Begonias? Yes fibrous rooted begonias are also known as wax begonias.

Can I overwinter fibrous rooted begonias in the house? Yes, they need morning sun, and be sure to keep the soil evenly moist. Begonias need high humidity so place the pot on a tray of damp pebbles to raise the humidity around the plant.

How do I store tuberous begonias for the winter? To keep tuberous begonias for another year, dig the tubers when frost threatens. Dry them in a protected, shady, well-ventilated spot, remove any excess soil, and store in boxes or shallow trays in a cool and dry location. Do not store any rotting bulbs.

What side is up when planting tuberous begonias? Always plant tuberous begonias with the concave (cup) side up. You may be able to see some pink new growth on top and old roots on the bottom. Cover with one inch of soil when planting.

Do I need to deadhead my begonias? Fibrous begonias are self-cleaning and do not need to be deadheaded. Tuberous begonias have heavy fleshy flowers and spent blossoms should be removed to prevent botrytis as well as other diseases.

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