Do commercial fertilizers like Miracle-Gro contain calcium?
Written by
Tina Carter
Reviewed by
Prof. Charles Hartman, Ph.D.Many gardeners mistakenly believe that commercial fertilizers, such as Miracle-Gro, provide all the nutrients, including calcium, that tomatoes would need. The certainty is that the average commercially available fertilizer does not supply enough calcium, and it has high nitrogen levels that inhibit calcium absorption. Understanding the analysis of a fertilizer will help clarify its significance in addressing specific nutrient deficiencies.
All-Purpose Formulas
- Standard 24-8-16 blend contains 0% calcium
- High ammonium nitrogen blocks calcium uptake
- Excess potassium creates nutrient competition
Specialty Tomato Formulas
- 18-18-21 version includes 1.3% calcium
- Insufficient for deficiency correction (needs 5-10%)
- Nitrogen still exceeds calcium ratio requirements
Performance Limitations
- Calcium binds to phosphates in granular forms
- Quick-release nitrogen promotes leafy growth over fruit
- Lacks magnesium balance for calcium assimilation
High nitrogen formulas create barriers to calcium absorption. Ammonium nitrogen will acidify the roots, locking up calcium in the root zone. Additionally, rapid growth resulting from nitrogen overload will increase the demand for calcium to a level beyond what is available. Due to these factors, typical Miracle-Gro is not a suitable option to correct a current deficiency. However, it may contain a small amount of calcium.
Specialty blends still do not adequately address deficiencies. Their 1.3% calcium content is only enough for maintenance. To correct blossom end rot, you will need fertilizers that have a calcium concentration of 15 to 20%. I learned this after several unsuccessful seasons of using only commercial products.
In a strategic approach, combine Miracle-Gro with calcium supplements. The all-purpose formula mist is best used early when plants are in a vegetative growth stage. Calcium nitrate can be used during the fruiting phase. At the same time, gypsum is recommended as a soil supplement and can be incorporated before planting the crops. This layered approach in the garden, using Miracle-Gro and calcium products, proved to be more effective than using a single product.
In situations of extreme deficiency, it is best to avoid using any commercial blends altogether. Utilize dedicated calcium sources, such as foliar sprays and soil amendments, to ensure optimal calcium levels. In all cases of fertilization, it is always recommended to test the soil in advance to match your inputs to the actual needs. Your tomatoes will thank you in the end by offering characteristic, pristine fruit.
Read the full article: Calcium Deficiency Tomatoes: Prevention and Solutions
