Tomatoes have their own peculiar magnesium needs compared to other vegetables, requiring more than the heavier crops but less than the root vegetables such as potatoes. I have also measured this deficiency using tissue tests on various plant species. Heavy-bearing varieties, especially, require a significant amount of magnesium during the critical periods of their growth and development.
Comparison to Other Crops
- Higher needs than lettuce/spinach (25-50 ppm range)
- Lower needs than potatoes/beets (100-300 ppm range)
- Peppers and eggplants share similar requirements
- Root vegetables need most magnesium for tuber development
Optimal Soil Levels
- Sandy soils: 50-120 ppm magnesium concentration
- Loam soils: 80-150 ppm magnesium concentration
- Clay soils: 100-200 ppm magnesium concentration
- Varies with cation exchange capacity and organic content
Critical Growth Phases
- Flowering: Magnesium supports pollen viability
- Fruit set: Essential for cell division initiation
- Fruit enlargement: Required for sugar transport
- Ripening: Influences flavor compound development
Large producers need extra attention. Beefsteak varieties require 30% more magnesium than do the cherry types. I increase the applications of these foods on these plants during the period of greatest production. The determinate varieties require a steady supply of these foods. At the same time, the indeterminate types benefit from these foods being supplied slowly.
Modify various reactions. Monitor beefsteak tomatoes during fruit growth. Cherry required a consistent supply throughout the production process. Test soil once a month for heavy producers. This prevents deficiencies in periods of greatest demand and ensures marketable quality.
Balance magnesium with the other elements. Tomatoes require a proper balance of calcium and magnesium. I keep it 4:1 in sandy soils, and 6:1 in heavy soils. This will eliminate blossom end rot and aid in photosynthesis. I test regularly in order to keep a proper balance for each specific variety grown.
When testing leaf tissue for accuracy, I consider the oldest leaves during the flowering period. An acceptable range for magnesium content in leaves is approximately 0.3 - 0.6%. I currently send samples to labs every three weeks. This direct measurement will verify soil test data used for more accurate modifications.
Read the full article: Magnesium Deficiency Tomatoes: Complete Grower Guide
