Twenty nutrients have been identified as essential for good plant growth, and 17 of them are found in healthy soil. Nitrogen, phosphorous and potassium are needed in the highest amounts; they are called macronutrients. Calcium, sulphur and magnesium are also important macronutrients. Organic plant fertilizers contain these essential macronutrients and a range of micronutrients that ensure balanced nutrition for plants. Plants require fertilizer during three important times in their growth cycle.
Plant fertilizer applied at the beginning of the growing season encourages strong root structure development. Plants absorb nutrients through their root system. Nitrogen stimulates dark green vegetative growth and potassium improves disease resistance. Magnesium is essential for chlorophyll production. Increase the nutrient content of soil and it increases the nutrient content of vegetables. A 2007 study by the University of California-Davis showed that tomatoes grown in nutrient-rich organic soil have 79 percent more flavinoids, which are important in cancer prevention. Healthy soil makes healthy food.
Fertilizer applied in mid-growing season can be broadcast, watered into the soil or spread in a band around the plant base. Plants in mid-season feed heavily on soil nutrients as they develop fruit and flowers. The boron and sulphur in organic plant fertilizer is essential for seed, root and fruit development. There are billions of tiny living organisms in natural plant fertilizers that release their nutrients slowly. Synthetic fertilizers release the chemical nutrients all at once, and the plant may not be able to absorb it.
Plants have used large amounts of nutrients during the growing season and benefit from nutritional input after harvest. Organic plant fertilizers such as compost can be spread on topsoil as mulch. The fertilizing nutrients slowly leak into the soil as autumn rains begin or the garden vegetation naturally starts to decompose. Apply one to three inches of compost fertilizer to each plant as it comes to harvest. Soil structure also improves from the addition of decomposing plants and organic fertilizer. In the spring, soil is looser, darker in color and ready to plant.