FERTILIZING TREES AND SHRUBS

Nutrient Requirements

Nutrient requirements of plants vary according to the variety of trees and shrubs, their stage of growth and the conditions under which they are grown. Fertilizing will only aid plants that have been properly maintained and located.

Soil contains two major nutrients, phosphorus and potassium. The pH level refers to the degree of acidity or alkalinity present in soil. Generally, a pH of 5.0-7.5 favors healthy growth of most plants. Do-it-yourself soil testing kits are available to test pH and nutrient levels.

Fertilizer Types

Fertilizers are available in different forms such as liquids and dry mixes; and formulations, including organic and non-organic. Generally, fertilizers contain three main elements:

• nitrogen, which promotes rapid growth and affects the greenness of leaves
• phosphorus, which promotes root development, branching and flowering
• potassium which promotes growth, making the plant more resistant to temperature and disease

The amount of each nutrient is listed as a ratio such as 10-10-10, or 20-10-10. The first number corresponding to nitrogen, the second phosphate and the third potassium. Some formulas also contain small amounts of micronutrient elements such as copper, iron, and zinc.

Organic Fertilizers

Organic fertilizers include formulas of dried blood, fish and seed meals and horse or cow manure. The mix is broken down by soil microorganisms releasing nutrients into the soil.

Inorganic Fertilizers

Inorganic fertilizers release nutrients effectively and are absorbed quickly by the plant's roots.

Inorganic fertilizer is available in liquid formats, applied directly to the plant, and as dry mixtures, watered into the soil. Also, control-release formulas are available, slowly releasing their nutrients into the soil. Control-release formulas generally need stable soil temperatures no less than 70^oF, and no more than 90^oF to work effectively.

Applying Fertilizer

It is important to follow the manufacturer's instructions when determining the application rates of fertilizer and the correct application process. High concentrations of fertilizer can burn roots and foliage.

Most manufactured fertilizers are simple to use, highlighting the nitrogen-phosphorus-potassium ratio on the package, and offering clear instructions. Do-it-yourself fertilizer mixtures can be time consuming and can lead to irreversible consequences if not properly followed.

When to Fertilize

The frequency of fertilization will depend on the tree or shrub itself, and should be applied so that nutrients are available for the plant's growth season. Wait at least one year before fertilizing a new plant to enable it to establish its roots before stimulating new growth.

As most growing seasons occur in the spring, fertilizer should be applied in late winter or early spring, approximately four weeks before the first signs of new growth appear, or when the soil temperature is at least 40^oF. Additional applications to trees and shrubs with a later growth spurt can be made after the initial spring period.

Generally, trees and shrubs benefit from yearly applications of nitrogen, which can be applied safely up to mid-September. It is important not to fertilize plants with potassium or phosphorus as they enter the dormant period and prepare for fall. It would stimulate new root growth that would not have had time to prepare for the cold weather.

What Areas to Fertilize

The area to be fertilized will be determined by the breadth of the plant's absorptive roots. The root systems of shrubs usually extend just beyond their foliage, while a tree's roots generally cover a radius of two times the radius of the tree's crown. Fertilizer should not be applied directly on the tree trunk as this may cause burning.

Try these fertilizers

Pasquesi Home & Gardens recommends Glorious Garden's Tree and Shrub Food for all your tree and shrub fertilizing needs.

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