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Fertilizing 101
Fertilizing plants is on everyone's "Gardening To Do List", but should it be? If so, when and with what type of product? There are so many different fertilizers available that it is easy to become confused.
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 or phosphate 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, or potash, 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?
While proper fertilizing helps to promote healthy plants, it is important to remember that it also makes plants grow faster. While rapid growth is often very desirable to gardeners, there are situations when we want plants to grow more slowly.
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 by insects. For example, if an azalea is infested with lacebug, the feeding damage causes yellow leaves. When the gardener looks at her plant and sees yellow leaves she may think the plant requires feeding. Fertilizer encourages new growth that hides the yellow leaves with fresh green ones. The gardener may think that she was correct in fertilizing the azalea since it now appears healthy; however, the lacebugs were never controlled. 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 "pushed" by fertilizer to increase their rate of growth.
Some plants are considered "heavy feeders" including roses and annuals. These plants bloom for extended periods of time and require plenty of fertilizer to provide top performance. Other plants require little or no fertilizer to remain healthy.
Mature trees and shrubs need to 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?
It is important to understand the role that rising and falling temperatures play in deciding when to fertilize. A consistent pattern of irregular temperatures in the spring and fall seems to be occurring in our area. We can experience days or weeks of unseasonably warm temperatures followed by a killing freeze.
If you fertilize during one of the first cool snaps in the early fall and then the temperatures become unseasonably warm, the plant is more likely to produce new growth and/or the flower buds may begin to swell. The cold weather that follows will kill off the new growth and flowers. Therefore, it is best to fertilize in late November when the temperatures are more consistent. The reverse is true in the spring. It is best to fertilize again in late February before the temperatures begin to rise.
Most plants can be fertilized in the late fall and then again in the very early spring. 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. Do not use a fertilizer if the plants that you want to feed are not listed. 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. A benefit of using water-soluble fertilizers is that you are watering the plants as you fertilize.
There are a few important things to remember about water-soluble fertilizers, however. While the prices of water-soluble fertilizers appear lower than granular fertilizers, water-soluble must be used approximately every 10 days (or as indicated on the package) where granular are used monthly or once a season. The other important factor is that liquid fertilizers need to be used as often as directed in order to be effective. If you do not have time to liquid feed regularly, it would be better to use a granular fertilizer.
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 dug or watered into the ground. Granular fertilizers are appropriate for all types of plants and are convenient because they do not need to be applied as often.
Many gardeners use a combination of the two types of fertilizers on plants that are heavy feeders. They use granular fertilizers initially and then supplement with a monthly liquid feeding. While this extra fertilizing is fine for annuals and roses, it should be avoided for trees and shrubs.
How Much Fertilizer Should Be Used?
Over-fertilizing plants causes soft stem growth and the excess fertilizer could pollute the groundwater. It is important to follow the manufacturer's directions carefully.
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