Step-By-Step to Fertilize Existing Soil for Planting

Soil Testing

• Most garden soil benefits from testing unless it has successfully grown plants with similar needs previously. A home testing kit, available from many garden centers, is sufficient in most cases. These kits provide the soil pH range and they may also indicate the availability of certain nutrients, such as phosphorus. Testing methods vary, but usually you must dissolve a soil sample in water and test it with the liquid or test strips provided. The liquid or strips change color to indicate pH or nutrient levels, so you simply match the color of your sample with the chart provided. If the pH is too low for the plants you will grow, add limestone to the bed in the amount indicated by the test results. If it's too high, you add sulfur. Work amendments that alter pH into the top 8 to 12 inches of soil at least three months before you plant.

Organic Amendments

• The structure of the soil is vital to healthy plant growth. Dense, clay soil provides poor aeration and drainage, while sandy soil contains few organic nutrients and dries too quickly. Loam soil has a crumbly texture that retains sufficient moisture while still draining well. It is also usually rich in organic material. Compost or composted manure improves the quality of the soil structure and even benefits loam soil. Spread a 2- to 4-inch layer of compost over the top of the soil before you plant. Tilling it into the top 6 to 10 inches of soil improves the quality throughout the root zones of most plants.

Fertilizer

• Fertilizer needs depend on the existing nutrient availability in the soil and the needs of the plant variety. The fertilizer label details the ratio of each of the major plant nutrients by showing the N-P-K amounts, which stands for nitrogen-phosphorus-potassium. Most fertilizers also contain other trace nutrients, which are detailed on the label. For example, a general purpose or balanced fertilizer may contain 10 percent of the major nutrients and be labeled 8-8-8 or 10-10-10. Fertilizer labels usually supply application rate recommendations based on the type of plant. In a vegetable garden, the label may advise applying 1 pound of 15-15-15 ratio fertilizer for every 50 square feet of bed.

Application Method

• Amendments for altering pH, such as lime and sulfur, are added first. Broadcast the amendment evenly over the soil and till it in with a power tiller or turn it in with a spade. You can add compost and fertilizers at the same time, usually right before you plant the garden. Nitrogen in particular washes from the soil quickly so shouldn't be added in advance. Spread both the compost and fertilizer evenly over the soil and till it in to the root zone, or the top 6- to 10-inches of soil. When fully incorporated, the soil should have a loose, crumbly texture. Avoid walking on the soil and compacting it, otherwise plant roots may not establish well.