Components of fertilizer
The three primary nutrients plants need are nitrogen (N), phosphorus (P), and potassium (K). These are available in chemical/synthetic (nonorganic) fertilizers. The numbers of each nutrient indicate the percentage of net weight contained. For example, a100-pound bag of 10-10-10 contains ten pounds of each element.
Nitrogen promotes strong leaf and stem growth and dark green color, such as desired in broccoli, cab-bage, lettuce, and herbs. Add aged manure to the soil and apply alfalfa meal or fish or blood meal to increase available nitrogen.
Phosphorus promotes root and plant growth, including setting blossoms and developing fruit, and seed formation; it’s important for cucumbers, peppers, squash, and tomatoes—any edible that develops after a flower has been pollinated. Add (fast-acting) bonemeal or (slow-release) rock phosphate to increase phosphorus.
Potassium promotes plant root vigor and disease and stress resistance and enhances flavor; it’s vital for carrots, radishes, turnips, and onions and garlic. Add green sand, wood ashes, gypsum, or kelp to increase potassium.
What to Know About pH
It’s important that garden soil has the proper soil pH. A very high or very low soil pH may result in plant toxicity or nutrient deficiency. A pH value of 7 is neutral; microbial activity is greatest and plant roots absorb/access nutrients best when the pH is in the 5.5 to 7 range.
When to Fertilize
Woody plants and perennials absorb nutrients from the soil during the growing season; they require few nutrients while dormant. Therefore, apply fertilizer as soon as the plants begin breaking dormancy in the spring. Follow instructions on the label as to how often to apply (this depends on the type of fertilizer used). Stop applications after the first fall frost. Food crops also benefit from an early-start fertilizing schedule. Some “feed” on fertilizers lightly, others are considered heavy feeders, and require more regular applications throughout the growing season.
Choosing Fertilizer: Granular Vs. Soluble
Granular fertilizers are solids that must be worked into the soil and given time (and water) before they dissolve and become available to plants.
Slow-release fertilizers are a subset of granular formulations. A portion of the fertilizer is not immediately available to the plant. Nutrients are metered out over several weeks. Therefore, they are applied less frequently.
Sometimes called “liquid feed,” soluble fertilizers are sold as either ready-to-use solutions or as packaged dry-milled materials that need to be dissolved in water. These tend to be quick-release fertilizers high in nitrogen that result in fast green growth.