Why aren't crushed eggshells fixing my tomato calcium issues?
Written by
Tina Carter
Reviewed by
Prof. Charles Hartman, Ph.D.Crushed eggshells are not an immediate solution for calcium-deficient tomatoes because plants cannot directly use the calcium carbonate present in the eggshells until microorganisms decompose it. Decomposition typically takes 6-24 months, whereas tomato deficiencies primarily affect the current growing cycle. Ground eggshells are best used as a long-term addition to soil, particularly for their calcium content. Not an emergency solution.
Chemical Transformation
- Calcium carbonate requires conversion to soluble calcium ions
- Soil microbes must break down chitin-protein matrix first
- Acidic soils below pH 6.0 accelerate decomposition
Preparation Requirements
- Must be ground to flour-like consistency using blender
- Vinegar pre-treatment increases solubility slightly
- Requires incorporation into top 6 inches of soil
Environmental Factors
- Decomposition halts below 55°F soil temperatures
- Requires consistent moisture for microbial activity
- Complete breakdown needs 4-6 microbial life cycles
Eggshells will release calcium into the environment over time, utilizing slow biological processes. Soil fungi, such as Trichoderma, will need to break down the organic matrix of the eggshells before any calcium can be derived in soluble forms that are plant-available. This will not happen fast enough to correct an active deficiency. My soil tests revealed no measurable increase in calcium during the first growing season.
Proper preparation of eggshells can help you benefit from them in the long term. To prepare the shells for beneficial use, apply heat for twenty minutes at 200°F to sterilize the shells. Then, place the shells in a blender and blend until they are finely ground into a powder. Mix with vinegar to yield soluble calcium acetate. This can be used when preparing your soil in the fall for next year's tomato crop.
You can crush eggshells and mix them with metabolic enhancers, then add them to a compost pile along with your coffee grounds for added acidity. You can also put eggshells in a worm bin, where worms will grind the shells finer. You can use an inoculate that contains Bacillus subtilis (-f), which is primarily an aerobic metabolite enhancer, but can also function anaerobically. All of these methods will lower the time for egg decomposition by 30%.
When dealing with active deficiency, rely on fast-response alternatives. A calcium chloride foliar spray identifies and corrects issues within 48 hours. Gypsum soil drenches are effective in 7-10 days. However, I consider this a relatively slow process compared to a calcium chloride foliar spray. Liquid bone meal also provides organic, quick relief. I try to have each of these on hand when I notice early symptoms of active deficiency.
Place eggshells intentionally as prevention. Work this into your practice on an annual basis to build up soil reserves. Use test kits once a year or at the start of each season to determine existing calcium levels. If done patiently, your calcium will occur sustainably after the initial season. Immediate interventions will protect your current harvest.
Read the full article: Calcium Deficiency Tomatoes: Prevention and Solutions
