Heat Overexposure

• Overexposure to heat generated by the midday sun may result in plant wilt. Each plant species grows in a specific climate. The USDA zone map divides the United States into zones based on the average annual minimum temperature of an area. These zones bear numbered designations from 1 to 11 (the higher the number, the warmer the region). Plants with little tolerance of heat wilt and even die when planted in too warm a zone. For instance, a plant suited for growth in zones 3 to 6 may exhibit wilt, abnormal growth, dieback, scorch and even death when grown in zone 10. Know your zone and always plant tolerant plants in the garden to avoid problems.
  
  

Light Overexposure

• Each species of plant expresses a tolerance of specific light conditions. Some plants grow ideally in full sun exposure, while others prefer partial sun exposure, partial shade exposure, light shade, deep shade and even full shade. When a plant suited for growth in any type of shaded condition grows in an area completely exposed to the sun for extended periods, overexposure to light results in a variety of problems, including leaf loss, wilt and scorch. Always check the light tolerance of a plant before planting it in area receiving full sun exposure. Remember that heat and light exposure constitute different things. Some plants with high heat tolerance only grow in the shade, while some species with a preference for full sun exposure only grow in temperate regions.
  
  

Wilt Diseases

• Wilts constitute a category of diseases that cause serious problems for a variety of plants, form vegetables and fruits to flowers, shrubs and trees. Examples include verticillium wilt, fusarium wilt, and tomato spotted wilt virus. The first visible symptoms of verticillium and fusarium wilts include increased wilt of plant leaves during the heat of the day, particularly on species not generally prone to heat wilt. Plants prone to wilt diseases suffer increased symptoms when overexposed to either heat or light. Generally, any problem a plant suffers, from excessive moisture to improper soil conditions, exacerbates diseases and encourages the presence of such problems.
  
  

Heat and Light Buildup

• Exposure to the mid-day sun may cause heat and light overexposure, though that may constitute just one component of a series of environmental conditions leading to overexposure to light or heat. Surfaces reflective of light and heat -- particularly asphalt, concrete, glass and metals -- increase the likelihood of heat or light overexposure by intensifying the effect of sun exposure. Such conditions create heat and light buildup. Areas with little air circulation also increase instances of heat damage by preventing the dispersal of heat over wide areas.