How and when to fertilize the garden can seem confusing, but once you understand some soil basics knowing how to care for your garden's soil is pretty clear. To start, it is important to know there are an awful lot of chemical reactions going on in the soil. These chemical reaction are what makes nutrients, such as nitrogen, phosphorus, and potassium, available for plants to use.
Since plants are using these nutrients up from the soil, we typically remove the plants from our garden either to eat or to prevent disease spreading. Therefore, through gardening we are removing nutrients from the soil and these nutrients must be replaced so next year's plants can grow and be healthy.
There are two ways we typically add nutrients back into the soil. One is through man-made chemical fertilizers and the other is through organic material and fertilizers. Both provide nutrients to plants, but they behave in very different manners.
Chemical fertilizers are readily available to the plants. All they need is a warm soil temperature and some water for the plants to be able to use the nutrients. The nutrients in organic matter come from something that once was alive. Horse manure once was grass. Blood meal comes from blood. For these nutrients to become available to plants, soil microorganisms must break down the organic matter. In addition to the soil microorganisms, this takes time, heat, and water. Nutrients from organic matter are released over many months into the soil.
Because organic matter is slow to release its nutrients, fall is an ideal time to apply them to the garden. This can be done by simply adding a layer of composted manure, shredded leaves, or compost to the top of the garden. There is no need to till in the soil. The soil creatures will do that work for you. Besides nutrients, these organic materials also add water holding capacity and structure.
Since chemical fertilizers are quick release, fall is not the ideal time to add these to the garden. By next growing season these could be washed away. If you want to add chemical fertilizer, be patient and wait until the spring.
Anne Lenox Barlow has had experience in the agricultural field as a horticulture educator with Cornell Cooperative Extension in Clinton County. She can be reached by e-mail at firstname.lastname@example.org.