Nitrogen Levels in Tomato Fertilizers

A fertilizer nitrogen level that's too high can have negative effects on tomato growth.

Fertilizer acts as a type of food for growing plants. Soil composition influences gardeners' decisions on the type of fertilizer to use and how often to apply it. Another consideration is the nutrient requirements of specific plants, like tomatoes.

Purpose and Composition of Fertilizer

The reason gardeners use fertilizer is to ensure that plants receive the nutrients required for healthy growth and fruit production. Three nutrients in particular are considered essential fertilizer components: nitrogen (N), phosphorus (P) and potassium (K). The proportion of each element is listed on commercial fertilizer products; for example, 10-20-10 (N-P-K). When purchasing fertilizer for tomatoes, look for ratios of 5-10-10, 5-20-20 or 8-16-16.

Nitrogen and Tomatoes

Tomatoes typically need higher levels of phosphorus and potassium in their fertilizer than nitrogen. Too much nitrogen can lead to little fruit production despite vigorous vine growth, poor color in ripe tomatoes, oddities in color change during ripening, and poor taste and texture of mature fruit.

How to Apply

Fertilizer for tomatoes should be worked into the soil approximately two weeks before planting. Once tomatoes have been set in the ground, a side dressing can be worked into the soil around plants. Common tomato side dressings include a nitrogen fertilizer added just after the first fruit appears, and gypsum, which provides needed calcium to prevent blossom-end rot.

References

• National Sustainable Agriculture Information Service: Organic Tomato Production
• Planet Natural: How to Grow Tomatoes--Organic Tomato Gardening
• University of Arizona Cooperative Extension: Fertilizer Application
• Ohio State University Extension Fact Sheet: Growing Tomatoes in the Home Garden
• Food & Fertilizer Technology Center: Excessive Nitrogen Causes Poor Coloring of Tomato
• Michigan State University Extension: N-P-K Fertilizers