Fertilizing Landscape Trees and Shrubs

Sustainment programs should be prepared for trees and shrubs on your landscape. A dependable sustainment plan includes checking and containing insect and disease problems, restraining weed competition, and doing timely applications of water, mulch, and fertilizer.

Tree and bush fertilization is particularly crucial in urban and suburban areas of the country where soils have been changed due to building. These urban lands incline to be heavily compressed, poorly oxygenated, poorly drained, and short of organic matter. Even where soils haven't been stricken, fertilization is possibly needed as part of a sustainment program to step-up plant vigor or to improve root or crest growth.

Trees and shrubs in residential and commercial landscape plantings are frequently fertilized to keep them healthy and attractive. Over-fertilization is prevalent, causing excessive growth, especially on young nursery stock. Trees growing in lawn areas usually receive some nutrients when the grass is fertilized. This is usually sufficient to maintain most trees in fertile soil. However, fertilization may be desirable on altered soils where unconsolidated fill material has been added or the topsoil has been removed. Managed urban areas where fallen leaves are taken off may also require a fertilization regime to enrich soil and replenish nutrients.

Plant nutrition is no stand-in for environmental factors, such as sunshine and water, which must be in equilibrium if a tree or bush is to acquire its full potential. Trees or bushes that are healthy and flourishing are more insusceptible to assault by insects and diseases. An application of fertilizer might, in a few cases, improve the plant's resistance to additional infestations of certain pests. For instance, maple trees will recoup from mild cases of Verticillium wilt after applications of nitrogen fertilizer.

Fertilizer Objectives

How and when to fertilize landscape trees and bushes hinge upon:
Sustainment aims (induce new vs. maintain existing growth)
Tree and bush ages (in general more for newer and less for older plants)
Plant strain levels

When to Fertilize

The best time to fertilize trees goes from late autumn, after the leaves have come down, through the winter and into early spring before new growth comes about. Fertilizer employed in the autumn has a lengthier period of time to infiltrate the soil enabling the roots to more efficiently assimilate it. The fertilizer is soaked up by the roots during the winter and is accessible to the plant for growth in the spring.
Trees that are rapidly developing should be fertilized annually. Well-established, adult trees usually call for fertilizer once every three to four years.

Newly Planted Trees Fertilizer Use

Newly planted trees usually do not need fertilizer during the first growing season. Most transplanted trees developed in the nursery have high levels of nutrients that last through the first growing season. Too much fertilization during the first year can damage the tree and reduce its rate of growth. After the first year, nitrogen can be applied in an approximately 3ft area around each tree. This will ensure a sufficient supply for continued growth. Do not apply fertilizer within 12 inches of the stem of the tree because fertilizer can burn and harm young stem tissue.

Determining the Need to Fertilize

Visual inspection of trees and shrubs is often the best overall factor to use in making fertilization decisions.
Look for:
Poor leaf color (pale green to yellow)
Reduced leaf size and retention
Premature fall coloration and leaf drop

Soil Test

18 nutrients are required by plants: carbon,oxygen, hydrogen, nitrogen, phosphorus, potassiu , calcium , magnesium, sulfur and 9 trace minerals: iron, boron, copper, manganese, molybdenum, zinc, cobalt , nickel and chlorine. Carbon , oxygen and hydrogen operate in the formation of plant cells and food fabrication, the first two furnished from the atmosphere and the latter received from water soaked up by roots.

A soil test furnishes specialised data on the potential for plant reaction to agricultural limestone and to phosphorus and potassium fertilizers. In addition it provides a verifiable basis for ascertaining how much of those elements to add once they are found to be lacking. A representative soil sampling can be a challenge to get, because most nutrient-absorbing roots of trees and bushes are in the upper six inches of the soil and may stretch out two or three times beyond the radius of the crown. Consequently, in determining the nutritional demands of trees and shrubs, it's also essential to look at soil and moisture conditions; the species, age and vigor of the plants; and previous fertilization.

Nitrogen, the most typically depleted soil nutrient, furnishes the greatest growth response. Unfortunately, soil tests or analyses for accessible nitrogen are not very dependable. Nitrogen is present in different forms (e.g. nitrate, ammonium, urea) and these forms can alter rapidly in the soil. All the same, overall tree growth, especially root and shoot elongation, leaf color and leaf size, can be heightened with increases of nitrogen. Be sure not to overfertilize with nitrogen. Don't overcompensate with greater amounts of nitrogen when fertilizing grass, bushes and trees. Nitrate leaches readily from numerous soils and can create water pollution problems.

Selecting a Fertilizer

A variety of fertilizer types exist:
Complete (N-P-K) vs. incomplete (one or more select nutrients)
Organic vs. inorganic
Fast release vs. slow release
Dry (granulated, pelletized, spikes, pulverized encapsulated) vs. liquid

To help determine the type of fertilizer to apply, consider the following: type of plant, time of year, desired rate of plant reaction, application methods and equipment cost, proximity to water sources, effect of soil type and pH, type of deficiency, and results of a soil test or other sampling method.

Nearly all landscape plants profit from a slow secreting nitrogen fertilizer that can be organic or inorganic. Remember that nitrogen is easily washed through the soil, but phosphorus and potassium are not, signifying they necessitate less frequent application.

Methods of Application

Fertilizers may be put on either directly or indirectly for plants. When sod is fertilized, tree and bush roots that stretch into the sod area absorb some of the fertilizer, and are consequently indirectly fertilized. Sod fertilization rates should be supplemented only if trees and bushes are demonstrating symptoms of nutritive deficiency.

Direct application of fertilizer may involve incorporation into the backfill soil or placement in the planting hole at planting time. However, the most common form of direct fertilizer application, broadcasting, is generally the most effective, especially relative to cost. Simply placing the desired fertilizer over the soil atop the tree and shrub roots and watering it in is usually adequate. Compacted soil should first be aerated or raked.

The most serviceable and expeditious way to fertilize sizeable trees is to disseminate granular fertilizer on the surface of the dirt and permit rain or irrigation water to move the nutrients down to the roots. Uniformly disperse the fertilizer over the area to be fertilized - that expanse covering the outer two-thirds of the distance between the tree trunk and the drip line and extending at least 50 percent of the crown radius beyond the dripline.

Another method is to put granular fertilizer into holes in the soil that are 4 to 12 inches deep. These holes are dug in a regular pattern at 2- to 3-foot intervalsl, in the same area as broadcast fertilizer is applied. Divide up the fertilizer among the holes. This technique does not insure consistent coverage to all feeder rootsl, especially in the upper few inches of the soil surface where the majority of the roots occur. High concentrations of fertilizers in these holes can also injure roots located bordering the hole.

A commonly used commercial method is to inject liquid fertilizers into the soil. A special injection rod is used and the fertilizer solution is injected under pressure. A comparable probe mechanism called a 'root feeder' is sold at most garden centers. The long probe attaches to a garden hose and water-soluble fertilizer cartridges distribute nutrients and water directly into the tree root zone. The tip of the injection needle should be inserted 4 to 12 inches into the soil at 2- to 3-foot intervals. Fertilizers suitable for liquid injection are typically more expensive per unit of nutrient and are frequently more difficult to apply than granular fertilizers.

Spikes are additional choice for tree or bush fertilization. These are rammed into the soil with a heavy hammer and can only be employed effectively when the soil is damp. The spikes don't evenly broadcast fertilizer around the tree's or bush's major feeder roots. Tree spikes are a pricey choice. Their popularity is founded on simplicity and ease of application.

Foliar feeding is a quick-fix solution when a nutrient deficiency has been found. The leavesl, buds and green wood are capable of a little nutrient absorption. Foliar nutrient sprays are applied with a pressure sprayer or siphon sprayer attached to a garden hose. The greening from foliar spraying is fairly quick but not long lasting. More often than not deficiencies of micronutrients including ironl, boron or manganese are corrected by seasonal foliar applications.

Micro-injection is the straight injection of essential nutrients into the trunk of the tree or shrub. It is a customary commercial practice for relieving or invigorating trees showing stress or decline symptoms. Nutrients can also be placed in gelatin capsules and set in in holes in the tree trunk. Micro-injection research is relatively limited and results are often conflicting. Drilling holes, implanting or injecting fertilizer and sealing holes can lead to trunk disfiguration and decay. Foliar applications, injections or implants should only be considered when soil application of fertilizer is not viable. These measures are considered short-term cures for nutrient deficiencies and pest infestations. Ultimately, the proper soil and foliar applications must be engaged for a long-term cure.

Placement of Fertilizer

Fertilizer shouldn't be focused around the base or trunk of a tree or bush, but should be put on as much of the plant's root zone as feasible. For trees and bushes, fertilizer ought to be put on an area double the crown spread. Because most landscape plant roots grow in the top foot of soil,shallow, not deep application, is suggested.

Factors Affecting Fertilizer Uptake

Many factors affect how well and well trees and shrubs absorb fertilizers. The most important uptake factors are:
Fertilizer form (inorganic, fast release, or liquid forms are absorbed faster than organic, slow-release,or dry forms)
Soil type (clay particles and organic matter soak up or bind more nutrients than sand, so fertilizer application needs to be more often in sandy soils, but with lower rates each time due to leaching potential)
Soil moisture content and soil warmth (nutrient uptake is faster in moist warm soils)
Plant vitality (plants under stress are less able to take up available nutrients due to damaged or reduced root systems)

Timing of Application

Fertilizer should be utilized when plants require it, when it will be most efficacious, and when plants can readily accept it. Late summertime and early autumn fertilization may hasten new growth that is not winter hardy, and summer drought could interfere with nutritive uptake, but spring, fall, and wintertime applications are satisfactory. A split application might be advantageous, applying half the annual rate in early spring and the balance in the fall as or after plants go dormant.
If water is unavailable, don't fertilize altogether - plants will be unable to assimilate the nutrients. (During a dry time of year, fertigation - application of fertilizer by means of an irrigation system can be beneficial.)

Tree and bush fertilization comprises only one part of aggregate plant maintenance. Fertilization might not benefit a plant if it's under stress from inadequate soil aeration or drainage, sodden soil, deficient light or space, or excessive pest problems. Altogether factors determining plant growth should be kept at optimal levels to guarantee plant vigor.

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