Common Tomato Problems

It’s the greatest time of year: tomato time!  Tomatoes have a few common problems that are usually solved by proper watering.  If you have a more serious problem, virus or soil-borne disease, let us help!  Snip an infected portion of the plant or snap a few good photos, then bring it to us for diagnosis.

Blossom End Rot

Blossom End Rot is a result of growing conditions, not a disease.  The blossom end develops a sunken, dark spot.  It’s caused by a lack of calcium and improper watering. Most Colorado soil contains enough calcium, but improper watering causes pH imbalances, which can bind the calcium and hold it unavailable to the roots. It can also be caused by excess nitrogen in the soil.
Preventing Blossom End Rot:
  • Remove and discard affected fruits.  They will not heal.
  • Pay close attention to your watering habits and always check the soil for moisture before watering. Water deeply-soaking the entire root ball, and infrequently-every 4-5 days, depending on exposure, temperature, etc.
  • Preserve affected plants by using a fertilizer or supplement with calcium.
  • Mulch around plants to conserve moisture.
  • When flowers begin to develop, use a high phosphorous fertilizer (5-8-5) to increase flower production.
  • Determinate tomato varieties are more prone to blossom end rot because they set fruit in a short time period.  Indeterminate plants set throughout the season, making it easier for plants to regulate calcium.


Intense, direct sunlight during very hot weather can discolor patches on ripening tomatoes.  It develops on the side that faces the sun.  The tomato is still edible, just cut out the discolored portion.
Preventing Sunscald:
  • Don’t over-prune plants.  Stems and foliage will shade the fruits.
  • Fertilize tomatoes when they are young to encourage plenty of foliage growth.
  • Use tomato cages.  The cage is designed to support the weight of the plant and you won’t need to prune.
  • If your plants don’t have enough leaves, shield plants with white shade cloth during the middle of the day.


Excessive watering following a dry period is the main cause of cracking.  When a tomato receives too much water too fast, the interior grows quickly and expands too fast.  The tomato skin can’t stretch to accommodate the extra fluid and the cracking alleviates pressure inside the fruit.  Some varieties are more prone to cracking than others.
Preventing Cracks:
  • Mulch around plants to maintain consistent moisture.
  • Water consistently.  Always check the soil for moisture before watering, and check every morning and night.
  • Use organic fertilizer and don’t over-fertilize.  Excessive, readily available nutrients can cause quick growth spurts.


Psyllids are tiny insects that inject their toxic saliva into leaves and cause “psyllid yellows,” yellow leaves with purple veins.  Both the nymph and adult secrete white granules that look like sugar, which is more recognizable than the insect.  Growth is stunted and leaves may curl.
Controlling Psyllids:
  • Encourage beneficial insects by planting species that attract lacewings and ladybugs.
  • Remove infected portions.
  • Sulfur dust or insecticidal soap are two organic options that may be used to control psyllids.