Calcium and Magnesium Fertilizer for Crops: Deficiency Guide and Solutions

Calcium and magnesium deficiency is paradoxically common even in soils that contain adequate total levels of these elements. The problem is not usually a lack of calcium or magnesium in the soil — it is a lack of plant-available calcium and magnesium, or an imbalance between these nutrients and competing cations (potassium, sodium, ammonium) that reduces uptake.

Calcium is unique among plant nutrients because it moves through the plant almost exclusively via the transpiration stream — it is carried from roots to leaves and fruit by the flow of water through the xylem. This means that any factor that reduces transpiration (high humidity, low light, poor air circulation) can cause localized calcium deficiency in rapidly growing tissues even when the root zone has adequate calcium.

Calcium deficiency symptoms appear first in the youngest, most rapidly growing tissues — new leaves, shoot tips, and developing fruit. In tomatoes and peppers, the classic symptom is blossom end rot (BER): a dark, sunken lesion at the blossom end of the fruit caused by calcium deficiency in the developing fruit tissue. BER can affect 20-30% of the fruit crop in severe cases, causing significant economic losses.

In apples and pears, calcium deficiency causes bitter pit — small, brown, corky spots in the flesh of the fruit that make it unmarketable. In lettuce and other leafy greens, calcium deficiency causes tip burn — browning and necrosis of the leaf margins on the youngest leaves. In all cases, the solution is to improve calcium supply and transport, not just to add more calcium to the soil.

Magnesium is the central atom in the chlorophyll molecule — without adequate magnesium, plants cannot produce sufficient chlorophyll for photosynthesis. Magnesium deficiency causes interveinal chlorosis (yellowing between the leaf veins while the veins remain green) on older leaves first, as the plant remobilizes magnesium from older tissues to support new growth.

The economic impact of magnesium deficiency is often underestimated because the symptoms develop gradually and are sometimes confused with other nutrient deficiencies or diseases. In fruit crops, magnesium deficiency reduces photosynthesis efficiency, which directly limits the carbohydrate supply available for fruit development. Research has shown that correcting magnesium deficiency in citrus and mango orchards consistently improves fruit size and sugar content by 10-15%.

The most effective calcium fertilizer for crops is calcium nitrate (15.5-0-0 + 26.5% Ca). It provides calcium in a highly soluble, immediately available form while simultaneously supplying nitrogen as nitrate — the preferred nitrogen form for most fruiting crops. Calcium nitrate is 100% water-soluble and compatible with drip irrigation and foliar spray applications.

For magnesium, the most effective fertilizer is magnesium sulfate (Epsom salt, 9.8% Mg + 13% S). It is highly water-soluble, immediately available, and compatible with most other fertilizers. For foliar correction of magnesium deficiency, apply a 1-2% magnesium sulfate solution (10-20 g/L) as a foliar spray. For drip application, use 5-10 kg/ha per application.

Prevention is far more cost-effective than correction for calcium and magnesium deficiency. The key preventive measures are: (1) Soil pH management — maintain soil pH at 6.0-6.5 to maximize calcium and magnesium availability; (2) Balanced fertilization — avoid excessive potassium or ammonium nitrogen applications that compete with calcium and magnesium uptake; (3) Regular foliar applications — apply calcium and magnesium foliar sprays at key growth stages as insurance against deficiency.

GreenGrow's micronutrient complex includes chelated calcium and magnesium in a balanced formula designed for foliar application. Applied every 14-21 days during critical growth periods, this product provides reliable insurance against calcium and magnesium deficiency across all crop species. Contact our agronomists for a customized calcium and magnesium management program for your specific crops and soil conditions.