To ensure healthy plant growth fertilizers containing nutrients may be added to the soil, but this is only necessary when the soil is unable to provide adequate amounts of the nutrients required. In general only nitrogen (N), phosphorus (P), and potassium (K) need to be added regularly. The percentages of these nutrients are labeled on fertilizer packages. Three numbers, always in the same order (NPK), identify the ratio of these elements: 5-10-5, for example means 5% nitrogen, 10% phosphorus and 5% potassium.
Plants respond differently to larger or smaller amounts of each element. Nitrogen aids in strong leaf and stem growth and promotes dark green leaf color. Too much nitrogen causes an abundance of soft foliage and delays flowering and fruiting, while an insufficient amount causes stunted growth and yellowing leaves.
Phosphorus encourages root development and also aids in the development of flowers and fruit. Phosphorus is also excellent for transplants. An insufficient amount causes stunted growth and delayed bearing of fruit.
Potassium improves general plant hardiness. It also helps in seed production and improves the size and quality of the flowers and fruit. A deficiency reduces flower and fruit size.
Which Plants Need Fertilizing?
Never fertilize trees and shrubs that are in poor health without first identifying the cause of the plant’s illness. Fertilizing a plant under stress, due to lack of water for example, will only further the plant’s decline by encouraging new growth at a time when the plant cannot adequately support its existing growth. If a plant is under attack from insects or disease, the use of fertilizer will only disguise the symptoms by encouraging new growth that is not damaged. For example, if an azalea is infested with lacebug, the feeding damage causes yellow leaves. The bugs lay eggs on the plant and the cycle of damage continues next season. Several seasons of lacebug damage may kill the azalea.
Newly planted trees and shrubs should not be fertilized for the first year with anything except compost (including Leafgro, manure, etc.) or a B vitamin plant starter. It is important for new plants to develop their roots and become established before being encouraged by fertilizer to increase their rate of growth.
Mature trees and shrubs should be fertilized every 2 to 3 years if the surrounding lawn is not fertilized regularly. If the lawn is fertilized regularly, additional feeding of the trees and shrubs is not necessary.
When Should Plants Be Fertilized?
Most plants can be fertilized in the late fall and then again in the very early spring; however, wait to fertilize spring blooming trees and shrubs after they bloom in the spring. This will ensure that you do not encourage the plant to flower prematurely.
Fertilize annuals, vegetables, roses, and plants grown in containers throughout their growing season. Perennial plants can vary greatly in their fertilizing requirements. It is best to check a reference book or with us at the Nursery to see which of your plants need regular fertilizing.
What Type of Fertilizer is Best?
There are so many different types of fertilizer available that the choices are staggering! Read fertilizer packages carefully before choosing a particular brand. You will want to consider its effectiveness, ease of application and cost.
First of all, be sure that the plants you want to fertilize are listed on the label. You will find that most fertilizers are “all purpose” and will feed a wide variety of plants.
Next, consider how the fertilizer is to be applied. The easiest fertilizers to use are slow-release, granular types of products that are sprinkled on the ground once in the spring and last for the rest of the season. Many liquid fertilizers come with a hose attachment that is much easier to use than a watering can.
Finally, just as you may consider the cost per weight when purchasing groceries, you may want to investigate the cost per use of a fertilizer. Some fertilizers appear more expensive than others until you understand that they need only be used once or twice a season.
Natural vs. Organic
- Natural – A product derived from animal/biological, mineral, or plant sources, in a form substantially as it occurs in nature. The materials may be altered to put them into a physical form that allows them to be efficiently applied.
- Organic – Any substance containing carbon is, by technical definition, organic. Both naturally occurring and man-made products may be organic.
Water-Soluble vs. Slow-Released Granular
Water-soluble fertilizers (such as MiracleGro) are mixed with water and then applied to the plant. These fertilizers are fast acting and are terrific for annuals, vegetables, houseplants and roses.
Granular fertilizers (such as Hollytone, 10-10-10 and Osmocote) are very easily applied around the base of the plant. In general they do not need to be worked into the soil. Granular fertilizers are appropriate for all types of plants and are convenient because they do not need to be applied as often.
How Much Fertilizer Should Be Used?
Over-fertilizing can harm plants and pollute the groundwater. Follow the manufacturer’s directions carefully.