Tomatoes can grow in any soil condition if getting enough sunlight and water but will thrive with the proper nutrients. Avoid planting tomatoes in the same area two seasons in a row or where potatoes were planted the season before as disease can be present and passed to tender seedlings.
Tomatoes prefer a deep, loamy soil that drains well. For best results, add plenty of organic matter such as compost, manure, leaves or shredded newsprint to your soil and till under to loosen up the soil before planting. Take a soil sample to your cooperative extension office for testing to determine your soil's additive needs. Add fertilizer as determined by the testing results to soil before planting and continue to fertilize plants through the season with a low-nitrogen/high-phosphorus blend as directed.
Nitrogen's purpose is to assist in photosynthesis. Through photosynthesis, a healthy green plant produces the sugars it "feeds on" to grow. Tomatoes need some nitrogen, but too much results in plants that are huge and lush but produce little fruit. If your plant is starting to yellow or wilt, chances are your tomatoes' garden plot needs more nitrogen. Fertilizers will show a ratio of the main nutrients per pound, with the first number being nitrogen.
Potassium, often known as "potash" in potting soil or fertilizer ingredients, is paramount to all living things for healthy cell building. Tomatoes like all plants rely on potassium to build strong stalks and roots to support growing plants and fruit. Potassium is mostly naturally found in healthy soil and used slowly by plants. General applications of fertilizers or compost keep soil properly-balanced in potassium. On fertilizer ingredients, potassium is your second number in the ratio.
Phosphorus is the mineral needed most by tomatoes. Phosphorus is used to produce blooms (and, thus, fruit) as well as strengthen the root system. Seed production is done through using phosphorus-- again, since seeds are found inside plump, red, ripe tomato, plants given plenty of this mineral will produce plenty of fruit to achieve its goal. Phosphorus is the last number in the fertilizer ratio. Commercial fertilizers blended specifically for tomatoes will have the proper balance of nutrients.