Emmalea Ernest, Extension Fruit & Vegetable Specialist; emmalea@udel.edu
Early planted tomatoes should be receiving additional nitrogen (N) and potassium (K) applications as sidedress or fertigation at this time. The tomato section of the Mid-Atlantic Commercial Vegetable Production Recommendations includes specific recommendations for nutrient applications to tomatoes grown on bare ground and in plasticulture systems. Reproduced below is the table with recommendations for fertigating plasticulture tomatoes on sandy, low organic matter soils (higher nutrient requirements) and fine texture, high organic matter soils (lower nutrient requirements).
Adequate nitrogen is essential for plant growth, but potassium is especially important in fruiting vegetables like tomatoes. Potassium is a part of many vital processes in the plant, but related to fruit production it is involved in moving proteins and sugars into the fruit and regulating sugar production. Tomatoes without adequate potassium develop a ripening disorder called yellow shoulders, in which the top of the tomato fruit remains firm and turns yellow rather than red. Inadequate potassium can also reduce fruit yield and affect quality factors related to flavor in tomatoes. Potassium applications through fertigation should be initiated before flowering starts, with rates increasing later in the season as fruits form.
Fertigation Schedule Examples for Fresh Market Tomatoes
This table provides examples of fertigation schedules based on two common scenarios – sandy coastal plain soils (top chart) and heavier upland soils (bottom chart). Note that this schedule assumes that N and K are applied to the soil before planting, as well as through fertigation. Modify this schedule based on your soil test results and base fertility.
This table is from page 445 of the 2024-2025 Mid-Atlantic Commercial Vegetable Production Recommendations.