Can too much calcium harm tomato plants?
Written by
Tina Carter
Reviewed by
Prof. Charles Hartman, Ph.D.Excessive application of calcium creates additional challenges for growers. It can be a detriment to the attempt to grow calcium-deficient tomatoes. Too much calcium increases the soil pH level above 7.0, where key micronutrients become "sequestered". In balance, these nutrient levels may be adequate; therefore, you may observe distinct nutrient deficiency symptoms due to the excessive level of calcium and the pH issues it causes. Balanced nutrient supplementation is instrumental in avoiding these issues.
Nutrient Lockout
- High pH binds iron, manganese and zinc
- Creates interveinal chlorosis (yellow leaves with green veins)
- Reduces phosphorus availability by 40-60%
Soil Structure Damage
- Excess calcium compacts clay soils reducing aeration
- Disrupts soil microbiome balance
- Forms hard surface crusts inhibiting water penetration
Plant Physiology Stress
- Thickens cell walls reducing fruit expansion
- Causes small, hard tomatoes with poor flavor
- Triggers early blossom drop reducing yields
Quickly address excess calcium. Use elemental sulfur to reduce soil pH at the rate of one pound per 100 square feet for each point of reduction required. Deep watering should be used to leach excess calcium from the soil and flush low-cation soils. Use chelated iron to address secondary deficiencies rapidly.
Avoid overloading by testing properly: Always conduct a soil test before any amendments are introduced. Your pH should fall in the 6.5-7.0 range for good nutrient uptake. Use calcium only when it is below 2000 ppm. I test every spring to keep from doing the same things I have done to a previous property.
Make smart choices in sources of calcium. Gypsum supplies calcium to the soil without altering the soil pH, making it a safer option than lime. Foliar sprays deliver direct applications to the plant, avoiding the accumulation of excess calcium levels in the soil. There are slower-release options, such as crushed oyster shells, that also mitigate calcium buildup. All my plants do well with gypsum applications.
Keep an eye on plants for early warning signs. For example, interveinal yellowing occurs before irreversible damage to the plant. Conducting soil tests every sixty days during your peak growth periods will help capture imbalances early and allow you to correct them. Balanced calcium will create strong plants that produce bountiful crops of perfect tomatoes year after year.
Read the full article: Calcium Deficiency Tomatoes: Prevention and Solutions
