Fertilization: How, When and Why
For plants to grow and thrive they need a number of different elements. Carbon, hydrogen, and oxygen are required, but these elements are plentiful in air and water, so we do not have to supplement them for our plants. Plants also require micro- and macro- nutrients. Micronutrients are found in the soil and they are needed in such small quantities that we do not usually need to provide our plants with these. The three macronutrients that plants require are nitrogen, phosphorus, and potassium. Nitrogen promotes growth of shoots and foliage, phosphorus promotes the growth of roots and flowers, and potassium helps strengthen a plant. When you look at a container of fertilizer, the three numbers on it are referring to the amount of available nitrogen, phosphorus, and potassium found in it. For example, 15-10-15 fertilizer has 15% nitrogen, 10% phosphorus, and 15% potassium.
Fertilizer comes in three different varieties- water soluble, granular, and slow release. Water soluble is mixed with the water you use to water your plants. It is generally applied once every two weeks. Granular and slow releases are mixed with the soil. They release their nutrients when they are watered. Granular fertilizer is generally applied once every four to six weeks. Slow release fertilizer can last from four to nine months. Always read label directions before applying.
Different plants have different fertilizing needs:
Most houseplants will benefit from an all-purpose fertilizer. Mix with water and apply as per package instructions throughout the growing season.
To keep your annual flowers blooming throughout the summer, choose a fertilizer with a high middle number, such as 10-15-10. Apply throughout the growing season following package directions.
Perennials can be fertilized throughout the growing season with an all purpose 20-20-20 fertilizer. Flowering perennials can be fertilized with a fertilizer with a high middle number, such as 10-15-10. As always, read and follow package instructions.
Shrubs and bushes
Fertilize your shrubs and bushes in the spring when they start to show signs of active growth. Use a 20-20-20 fertilizer and apply 1-3 times throughout the growing season, depending on the type of plant. If it is a flowering shrub or bush, you can fertilize once a week with a 15-30-15 fertilizer as long as it continues to flower.
Fertilize your trees when they start to show signs on active growth. Fertilize up to three times a season until mid-August. Do not fertilize in the fall, but be sure to keep your trees well watered.
Generally you can fertilize your lawn once in the spring and once in the fall. Use a fertilizer specially formulated for lawns. Fertilizing in the spring will promote green growth and fertilizing in the fall will prepare your lawn for the coming winter.
Keep in mind that these are guidelines only. Some plants have special fertilization requirements. Check with our experts at the time of purchase to see what the recommendation for that plant is.