1. Home
  2. Expertise
  3. Diseases & Pests Advice
  4. Begonia


Series: Volumia™, Bada Boom® (bronze leaf), Bada Bing® (green leaf), Varsity™(both bronze and green leaf), Braveheart®, Eureka™ (both bronze and green leaf)


1. Soil and pH Needs

Begonias like rich, loose and fertile soil which drains well. However, Begonias do not perform well in wet, poorly drained soils. Heavy clay soils will retard root growth and starve the plant of oxygen, which can lead to root diseases. Soil should be amended with fully composted organic matter prior to planting and in the case of clay soils the addition of Canadian sphagnum peat moss and well-rotted compost are good sources of organic matter that will aid in aeration. If possible, incorporate two to three inches of organic matter into the top six inches of soil. If adding organic matter, be aware that organic matter that has not been fully composted will tie up nitrogen and sulfur leading to nutrient deficiencies and poor growth.  Soil pH should be 5.5 - 6.2 for optimum nutrient uptake; and should be tested prior to planting but after adding any amendments. This can be done quite easily with a portable pH tester available for about $100. Mix one part soil with two parts distilled water, stir well and wait thirty minutes, then follow the instructions for using the pH meter. If pH is too low, the addition of lime is warranted. However, the rate will vary depending on how much you need to raise the pH and the type of soil you are dealing with. Clay soils or those with a lot of organic material have a high buffer capacity and require more lime than sandy soils, which have a low buffering capacity. A good soil testing lab can determine the lime requirement index (LRI) of your particular soil and can recommend types and rates of lime to use. The frequency of watering will depend on the type of soil, weather conditions and the amount of mulch. Mulch will not only reduce soil water evaporation but will also reduce splashing of water onto the lower leaves, moderate soil temperatures and reduce weed competition. Allow the soil to dry slightly between watering; if Begonias are kept too wet it will lead to problems with root rot.


2. Fertility

Begonias are low to moderate feeders in the landscape; and can have a landscape life of three – six months. An application of a balanced controlled-release fertilizer (CRF) such as 10-10-10 or 14-14-14 with a 3-4 month formulation applied to the bed at planting will keep the plants well fed, depending on the amount of irrigation required and the average daily temperature. In areas of high irrigation and high temperatures it may be better to use a formulation with a slower release rate since higher temperatures will cause the fertilizer to be released quickly. Fertilizers that are not CRF are not recommended since the fertilizer will be leached out of the root zone long before the crop needs the nutrients. In high pH soils (alkaline soils) additional iron or iron sulfate may be beneficial to reduce chlorosis (yellowing) of the foliage.  Yellow foliage on begonia may also be caused by a nitrogen deficiency within the plant. Both can be corrected with the proper supplemental fertilizers. 


3. Disease

Water correctly to prevent most of the fungal diseases that can cause problems for Begonia such as: botrytis, powdery mildew, and pythium.  Botrytis will develop as tan spots on the foliage. Established plants that are infected will rot at the crown, and the infected tissue will be covered with dusty gray fungal growth. Powdery mildew can be identified by a white fungal growth that develops on the leaves, flowers or stems. The tissue beneath the fungus may die. Pythium rot will develop as shiny, blackened areas on the stems and petioles of established plants.  These areas often occur at or just above the soil line and plants will ultimately collapse and die. The best preventative is to use drip irrigation. At the very least, direct water from the hose onto the soil or mulch, and not on the plants themselves. 


Typical symptoms of botrytis on Begonia


Powdery mildew on Begonia



4. Insects

You may find aphids, thrips or caterpillars on Begonias. Aphids are tiny soft bodied insects that cluster on the growing tips of leaves and flower stems, sucking plant juices. The plants become stunted and deformed. Thrips can feed on the upper surface of leaves leaving them silvery looking; they also like to feed on the pollen in the flowers which can distort their appearance. Caterpillars will feed on plant leaves and stems, often at night. Remember that healthy, vigorous plants are less susceptible to pest damage than unhealthy plants.  


Adult aphids



Adult Western Flower Thrips


Caterpillar damage


5. Tips for Success

  • The worst enemy of Begonias is having the roots standing in water.
  • Cool temperatures, high fertilization, and overwatering are the most common problems in the landscape.
  • Remove weeds from the plantings that compete with Begonia for moisture, nutrients and light.