Fertilizing Landscape Shrubs and Trees
Fertilizing Landscape Shrubs and Trees - Part I
Author: Marie Wakefield
Maintenance plans should be produced for trees and shrubs in your landscape. An effective care program includes monitoring and keeping insect and disease problems in line along with restraining weed competition, and giving well timed applications of water, mulch, and fertilizer.
Tree and shrub fertilization is especially important in urban and suburban areas of the country where soils have been altered due to construction. These urban soils tend to be heavily compacted, poorly aerated, poorly drained, and low in organic matter. Even where soils have not been affected, fertilization may be needed as part of a maintenance program to increase 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.
How and when to fertilize landscape trees and shrubs depend on:
Maintenance objectives (stimulate new vs. maintain existing growth)
Tree and shrub ages (generally more for younger and less for older plants)
Plant stress levels
When to Fertilize
The top time to fertilize trees extends from late fall, after the leaves have fallen, through the winter and into early spring before vigorous new growth occurs. Fertilizer applied in the fall has a longer time period to penetrate the soil enabling the roots to more efficiently absorb it. The fertilizer is taken up by the roots during the winter and is available to the plant for growth in the spring.
Trees that are fast growing should be fertilized yearly. Well-established, mature trees usually require 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.
Fertilizing Landscape Shrubs and Trees - Part 2
As part of your overall landscape plan, the importance of a care program which includes monitoring and keeping insect and disease problems in line along with restraining weed competition should be considered. Here is how to determine if fertilizer is needed-
Scrutinizing the trees and shrubs visually is frequently the best general factor to apply in arriving at fertilization decisions.
Bad leaf color (pale green to yellow)
Decreased leaf size and retention
Untimely autumn coloration and foliage drop
Decreased twig and branch emergence and retention
Overall decreased plant development and vigor
As well as detecting signs of possible nutritive deficiencies of the plants, soil and foliage analysis can be used to help ascertain or corroborate whether additional fertilization is needed.
Eighteen nutrients are essential for plants: carbon, oxygen, hydrogen, nitrogen, phosphorus, potassium, calcium, magnesium, sulfur and nine trace minerals: iron, boron, copper, manganese, molybdenum, zinc, cobalt, nickel and chlorine. Carbon, oxygen and hydrogen function in the formation of plant cells and food creation, the first two obtained from the atmosphere and the latter gotten from water absorbed 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, 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 over fertilize 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.
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 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.
NOTE: The fertilizer package has three numbers such as, 10-10-10. They represent, respectively, the percentage by weight of nitrogen (N), available phosphorus (P2O5) and water-soluble potash (K2O). These figures help you choose the right fertilizer and determine how much to apply. For example, a fertilizer labeled as 10-10-10 contains 10 percent N, 10 percent P2O5 and 10 percent K2O. The remaining 70 percent is usually inert filler.
Fertilizing Landscape Shrubs and Trees - Part 3
Remember first to consider the importance of a care program which includes monitoring and keeping insect and disease problems in line along with restraining weed competition. Then you need determine if fertilizer is needed. Then you will consider the various methods of applying fertilizer.
Methods of Application
Fertilizers may be put on either directly or indirectly for trees and shrubs. 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 broadcasting 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 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.
NOTE: Definition: The dripline is the area directly located under the outer circumference of the tree branches. This is where the tiny rootlets are located that take up water for the tree. Trees should be watered here, not by the base of the trunk, or the tree may develop root rot.
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 quick-fix solution when a nutrient deficiency has been found. The leaves, 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 iron, boron or manganese are corrected by seasonal foliar applications.
Fertilizing Landscape Trees and Shrubs Part 4
First there is the importance of a care program which includes monitoring and keeping insect and disease problems in line along with restraining weed competition was considered. Then how to determine if fertilizer is needed. Then some methods of applying fertilizer are required. This article considers another method of application, placement of fertilizer and timing.
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 imbedded in holes in the trunk. Micro-injection research is comparatively limited and outcomes are often conflicting. Boring holes, imbedding 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 should not be concentrated around the base or trunk of a tree or shrub, but should be applied over as much of the plant's root zone as possible. For trees and shrubs, fertilizer should be applied over an area twice as large as the crown spread. Since most landscape plant roots grow in the top foot of soil, surface, but not deep application, is recommended.
Factors Affecting Fertilizer Uptake
Numerous elements impact how easily and well trees and bushes assimilate fertilizers. The most significant uptake factors are:
1.Fertilizer variant (inorganic, quick release, or fluid forms are assimilated faster than organic, slow-release, or dry forms)
2.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)
3.Soil moisture content and soil temperature (nutrient uptake is faster in moist warm soils)
4.Plant vigor (plants under stress are more ineffective in assimilating available nutrients because of damaged or decreased root systems)
Fertilizer should be given when plants require it, when it will be most effective, and when plants can readily take it up. Late summer and early fall fertilization may rouse new growth that is not winter hardy, and summer drought may interfere with nutrient uptake, but spring, fall, and winter applications are acceptable. A split application may be beneficial, applying half the yearly rate in early spring and the rest in the fall as or after plants go dormant.
If water is unavailable, do not fertilize at all - plants will be unable to take up the nutrients. (During a dry season, fertigation - application of fertilizer through an irrigation system can be valuable.)
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 the growth of your beautiful shrubs, bushes and trees should be kept at optimal levels to guarantee plant vigor.