What's the optimal timing for calcium applications?
Written by
Tina Carter
Reviewed by
Prof. Charles Hartman, Ph.D.Just as importantly, calcium applications will effectively alleviate calcium deficiency in tomatoes when used at the right time. Suppose you use them too soon or too late. In that case, the treatment will be ineffective, even with the highest quality material. I have determined timing rules, which come from investing two decades growing tomatoes. This guide will share the windows that are most pertinent for soil and foliar applications.
Soil Amendments
- Lime/gypsum: Incorporate during fall prep for spring planting
- Bone meal: Apply at transplanting mixed with root zone soil
- Calcium nitrate: Side-dress 2 weeks after transplanting
Foliar Sprays
- First spray: Early morning at first fruit set appearance
- Symptom response: Apply within 24 hours of lesion spotting
- Maintenance: Every 7-10 days during rapid fruit expansion
Seasonal Maintenance
- Soil tests: Every 60 days from transplant to harvest
- Drip injection: Weekly low-dose calcium in irrigation water
- Weather response: Extra spray before forecasted heat waves
Morning applications are of utmost importance! Plant stomata are widest open in the morning before 10 AM for maximum foliar absorption of solutions introduced for the plants. Spraying in the afternoon results in the evaporation of the solution. In addition to using the proper spray solution during critical growth stages, I would set my alarm to spray at dawn for morning applications. By just changing the application time, I was able to double the effectiveness.
Weather conditions often determine the timing of an emergency. We recommend applying foliar sprays before predicted temperatures exceed 85°F. The heat stress increases the tree's demand for calcium. If we experience heavy rain that leaches calcium from the soil, you should also make an application. I monitor weather apps religiously during fruiting season.
Align applications with growth stages. The fruit set phase begins when flowers drop off and small tomatoes become visible. This is when I apply the first foliar spray. The second one occurs when the tomatoes reach a golf ball size. The third application occurs during the rapid expansion stage. I follow these stages on a calendar using these visual cues.
Steer clear of common timing errors. Never use soil amendments when the tree is bearing fruit. Disturbing tree roots greatly reduces nutrient uptake. Never spray the tree when it is flowering, as wet blossoms will abort. I learned the hard way and lost an entire crop following these rules. I now calculate accurately and time all applications just right.
Read the full article: Calcium Deficiency Tomatoes: Prevention and Solutions
