The ideal ratio for tomato fertilizer depends on the nitrogen level of the soil. For balanced soil or soil that is high in nitrogen, the ideal ratio is 5-10-5 or 5-10-10. For soil that is low in nitrogen, the ideal ratio is 8-8-8 or 10-10-10.
The ratio of a fertilizer refers to the concentration of nitrogen, phosphorus and potassium. A fertilizer that contains high level of nitrogen promotes leaf growth, which may not optimal for tomatoes at the initial planting stage, as this produces more leaves and fewer tomatoes. During the tomato season, a fertilizer that is high in phosphorus, such as one with a ratio of 0-46-0 or 4-12-0, is ideal.