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Fertilizing Your Landscape

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 important in urban and suburban areas of the nation where soils have been altered due to construction. These urbanized soils tend to be heavily compacted, badly aerated, poorly drained, and low in organic matter. Even where land has not been affected, fertilization may be needed as part of a maintenance program to step-up plant vigor or to improve root or top 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.

Fertilizer is no stand-in for environmental factors, such as sunlight and water, which must be in balance if a tree or shrub is to grow into its full potential. Trees and shrubs that are healthy and growing robustly are less susceptible to attack by insects and diseases. An application of fertilizer may, in some instances, improve the plant's resistance to further infestations of certain pests. For example, maple trees will recover from mild cases of Verticillium wilt following applications of nitrogen fertilizer.
Ash Tree's Before & After Deep root Fertilization

Objectives for Fertilizing

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.

Fertilizing Newly Planted Trees

Freshly planted trees typically do not need fertilizer during the 1st growing season. Almost all transplanted trees produced in the nursery have elevated levels of nutrients that last through the 1st growing season. Exuberant fertilization during the first year could harm the tree and cut back its rate of development. After the 1st year, nitrogen can be utilized in a roughly 3ft area around each tree. This will assure a satisfactory supply for continued development. Don't apply fertilizer within 12 inches of the stem of the tree since fertilizer can burn and injure young stem tissue.

How to Determine Whether 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, potassium, 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 specialized 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 frequently deficient soil nutrient, provides the greatest growth reaction. Regrettably, soil tests or analyses for available nitrogen are not very reliable. Nitrogen is at hand in several forms (e.g. nitrate, ammonium, urea) and these forms can change rapidly in the soil. However, overall tree growth, particularly root and shoot elongation, leaf color and leaf size, can be enhanced with additions of nitrogen. Be careful not to over-fertilize with nitrogen. Do not overcompensate with higher amounts of nitrogen when fertilizing grass, shrubs and trees. Nitrate leaches readily from many soils and can cause water pollution troubles.

Fertilizer Selection

An assortment of fertilizer types exist: Complete (N-P-K) vs. Partial (one or additional select nutrients) Organic vs. inorganic Fast release vs. slow release Dry (grained, pelletized, spikes, powdered, encapsulated) vs. liquid

To assist in determining the form of fertilizer to utilize, weigh these factors: type of flora, season, wanted rate of plant reaction, application program and equipment price, proximity to water sources, consequence of soil type and pH, type of deficiency, and outcomes of a soil test or additional sampling methods.

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.

Application Methods

Fertilizers can be applied either directly or indirectly to plants. When turf is fertilized, tree and shrub roots that extend into the turf area absorb some of the fertilizer, and are therefore indirectly fertilized. Turf fertilization rates should be supplemented only if trees and shrubs are showing symptoms of nutrient deficiency.

Straight application of fertilizer could call for placement into the backfill soil or positioning in the planting hole at planting time. Nevertheless, the more common variant of direct fertilizer application, broadcasting, is typically the most useful, especially proportional to cost. Just broadcasting the fertilizer over the soil atop the tree and bush roots and watering it in is generally enough. Compressed soil should first be aerated or raked.

The most sensible and efficient way to fertilize large trees is to scatter granular fertilizer on the surface of the soil and allow rain or irrigation water to transport the nutrients to the roots. Evenly broadcast the fertilizer over the area to be fertilized - that area covering the outer two-thirds of the distance between the trunk and the drip line and extending at least 50 percent of the crown radius beyond the dripline.

An alternative method is to position granular fertilizer into holes in the ground that are four to twelve inches deep. These holes are constructed in a regular pattern at 2- to 3-foot separations, in the same expanse as broadcast fertilizer is applied. Divvy up the fertilizer amongst the holes. This process does not insure homogeneous coverage to all feeder roots, particularly in the upper few inches of the soil surface where the bulk of the roots occur. Strong concentrations of fertilizers in these holes can in addition injure roots located next to 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 another alternative for tree or shrub fertilization. These are pounded into the soil with a heavy hammer and can only be used successfully when the soil is moist. The spikes do not evenly distribute fertilizer around the tree's or shrub's major feeder roots. These spikes are an expensive alternative. Their reputation is based on simplicity and ease of application.

Foliar feeding is a short-run answer when a nutrient inadequacy has been diagnosed. The leaves, buds and green wood are able to absorb some nutrients. Foliar nutrient sprays are put on with a pressure sprayer or siphon sprayer attached to a garden hose. The green-up from foliar spraying is fairly speedy but not long enduring. Generally deficiencies of micronutrients including iron, boron or manganese are rectified by seasonal foliar applications.

Micro-injection constitutes the direct injection of necessary nutrients into the trunk of the tree or bush. It's an acceptable commercial use for remedying or invigorating trees demonstrating stress or decline symptoms. Nutrients can as well be solidified into gelatin capsules and embedded in holes in the trunk. Micro-injection research is comparatively limited and outcomes are often conflicting. Boring holes, embedding or injecting fertilizer and sealing holes could lead to trunk disfigurement and decay. Foliar applications, injections or implants would better be used only when soil application of fertilizer is unrealistic. These routines are regarded as short-term remedies for nutrient deficiencies and pest infestations. In the final analysis, suitable soil and foliar applications must be applied for a permanent cure.

Fertilizer Placement

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.

How Fertilizer Uptake is Affected

Numerous elements impact how easily and well trees and bushes assimilate fertilizers. The most significant uptake factors are: Fertilizer variant (inorganic, quick release,or fluid forms are assimilated faster than organic,slow-release, or dry forms) Soil type (clay particles and organic matter assimilate or bind more nutrients than sand, so fertilizer needs to be applied more frequently in sandy soils, but with lesser rates each time due to leaching potential) Soil moisture content and soil temperature (nutrient uptake is faster in moist warm soils) Plant vigor (plants under stress are more ineffective in assimilating available nutrients because of damaged or decreased root systems)

Application Timing

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.

Marie Wakefield. For container landscape and other better landscaping ideas visit

Jomar Tree Service • P.O. Box 4803 • Cave Creek, AZ • 85327 – serving the Phoenix metro area – 602-285-0285