Fertilizing / Trunk Injections
The first year or two after planting is the most important time for watering and fertilizing. By this time, a young tree is getting its roots established and developing it’s limb structure. Providing care at this critical time will ensure bountiful rewards in the future with stronger, better shaped, more pest and disease resistant trees and shrubs. A good root system is the key to a healthy tree, and there should be a fairly balanced ratio between shoot growth and root growth.
Fertilizers come in a wide array, but there are two basic types that is organic (natural) and inorganic (chemical). All organic compost and fertilizers are derived from living material and contain the most essential building block of life carbon. Many people have become confused over the relative merits of organic versus inorganic aids for trees and shrubs. Most organic aids are generally longer lasting, and are considered more to be soil builders and thus they improve soil quality over time. Compost and manure, are good examples of organic soil builders. Working this organic matter into the soil before planting is the best basis for ensuring good growth and a healthy start for young trees.
Inorganic or (chemical) fertilizers as they are commonly known are a great way to provide a quick pick-me up or booster shot and can induce a temporary growth spurt.
( ammonium nitrate ) (potassium) (phosphorus) (sulfur)
(Examples of inorganic sources)
Unlike organic fertilizers, these are derived from mineral sources and so they do not maintain the essential humus levels on which the continued health of the soil depends. For that organic material is needed. Happily trees and shrubs supply their own humus by dropping their leaves and twigs. Leaving these to decompose where they fall is one of the few times in life that laziness is rewarded.
The results you achieve with your trees, is directly related to the degree of fertility in the soil, which is influenced by the type and amount of nutrients available. For instance, approximately 1/7 of protein is nitrogen, which is the element most used by all trees and green plants. It is important for both growth and development.
Nitrogen is an essential ingredient in most fertilizers but since it dissolves very easily in water, it is leached out of the soil more easily than other elements. Nitrogen exists in the protoplasm and chlorophyll of all trees and plants. It is an integral element essential for life and growth.
( protoplasts in an oak leaf )
( here under magnification you can see the green chlorophyll within a leaf tissue cell )
Too much nitrogen applied when fertilizing however, can be detrimental as it can cause overly fast and excessive canopy growth, while at the same time failing to initiate changes within the root system to compensate for the added growth. We have encountered this situation many times after storms i.e.(large trees completely uprooted or blown over on their sides only to reveal a small compact root system in relation to a broad canopy hence top heavy trees that are prone to blow over during weather related events) The problem is a common one where fertilization objectives are geared towards pushing turf growth i.e.( golf courses various neighborhoods or parks) Indeed more understanding of trees is needed.
This condition often times can create serious problems in relation to resource allocation. Trees allocate their limited resources in several ways, (growth, maintenance reproduction translocation of stored energy reserves throughout woody tissues in limbs, trunk and roots and in the production of allelo-chemicals related to defense against pathogens, insects and disease).
Interestingly enough, allelopathic chemicals also serve to suppress the growth of other trees growing too close to the parent tree. These allocation processes pose a considerable cost to the tree, and do not happen at the same rate. For example when trees are actively producing new foliage, there will be less energy reserves available for other needs and so fertilizing for the purposes of pushing growth can predispose trees to future problems, by depleting valuable reserves. If such a tree encounters a stress situation such as drought, it may not have the necessary energy reserves left over to prevent stress from going to strain, thus weakening the tree.
These overly fertilized trees are predisposed to disease or insect attack because of a gross imbalance in the ratio of shoot growth to root growth. Also they are more likely to be adversely effected if and when drought conditions ensue.Trees that have been given ultra- high nitrogen fertilizers also are less capable of withstanding temperature extremes and physical injuries. Other elements necessary to maintain a balanced growth rate are: potassium, phosphorus and iron. Potassium or (potash) strengthens stems and leaves and the holding quality of flowers on flowering species. Potassium is the main element that helps trees survive long periods of drought. Phosphorus helps in germination and development of seeds, provides rapid development of roots and is necessary for good flower color. Iron meanwhile, is vital to the growth and metabolism of trees and plants. Iron deficiency in the soil, will cause new growth to lack the greenness of a healthy tree. Iron poor trees and plants will often exhibit green veins in the leaves, while the remainder of the leaf turns yellow (chlorosis), a condition that can be remedied by fertilizing or foliar feeding (spraying) with chelated iron.
Most good fertilizers contain some iron in the formula. Certain trace elements also play important roles in tree metabolism. Calcium helps strengthen cell walls and assists in the development of fine root hairs.
(This is a view of a section of the fine absorbing root system of a live oak tree (Quercus virginiana) this section was excavated using an air spade)
It is important to remember, that these fine root hairs are absolutely vital for growth, because most nutrients are absorbed into the tree through them and not through the main woody structural roots, which serve more to anchor the tree. Magnesium is used in the cells of chlorophyll (green coloring), that assist in photosynthesis, which is the process by which trees convert sunlight into carbohydrates or (energy).
Magnesium also contributes in the distribution of phosphate within trees and plants. Manganese is another trace element, which is essential in transporting iron throughout a tree as well as helping the roots assimilate fertilizer, water, air and gases. Boron helps prevent the breakdown of structural tissues in the leaves and stems. Small quantities of copper and zinc are also needed by trees to strengthen the growth of young seedlings, and insure proper growth at maturity.
(Microscopic view of chlorophyll)
Sulfur is used in the formation of protein and aromatic oils in leaves and stems. Established trees also benefit from fertilizing, but it is essential to get the fertilizer down where the absorbing roots are. This is usually in the top 6 to 12 inches (15.24 to 30.48 cm.) of soil. There are several common methods of fertilization, some examples are: The deep root method (auger) which is used in conjunction with granular fertilizers.
Also the watering rod method is another good choice, and can be used with either granular or liquid fertilizers. It is a great way of providing deep watering and fertilizing at the same time.
There is also the broadcast spreader method, which is used in conjunction with granular fertilizers but this method is not very effective where competing ground cover is a factor.
There are other methods besides these, such as micro- trunk injection where nutrients, pesticides or antifungal agents are injected directly into the sap stream of the tree. It offers us a way of getting nutrients directly to the canopy of a tree while by-passing the root system. As far as nutrients are concerned, this process is usually used to deliver micro- nutrients to a deficient tree. Sometimes we are able to help trees that have sustained lightning strikes where the fine absorbing roots have been damaged thereby limiting water/ nutrient uptake or when tree roots have been injured by construction activities using micro- trunk injection methods.
It is always a good idea to obtain laboratory analysis of twig and leaf tissue as well as a soil sample before deciding to fertilize. This service is normally available through the university cooperative extension or the dept. of agriculture/ division of forestry. We can also assist you in this matter. It is important to remember that fertilizing carelessly will do more harm than good.
(micro-injection offers a great way to deliver nutrients, and pesticides systemically)
(Laboratory analysis can really be a great tool for determining necessary treatments)
(This tree's root system was burned by the over-application of fertilizers it will likley decline)
Finally no discussion on tree fertilization would be complete without covering the aspects of bio-fertility. First a brief history of fertilizer is in order. Originally fertility was added to soils using the all- important soil builders mentioned earlier, these would decompose slowly by bacterial action, gradually releasing their nitrogen and mineral/ nutrient content.
(Various soil bacteria under magnification)
For a long time the details of plant nutrition were largely a mystery. By careful study of plant physiology, scientists were able to identify the essential nutrients and to determine what forms of these nutrients trees could readily absorb. Once these were known , it was a simple matter to design mixed fertilizers hence artificial fertilizers were born. Studies in forest biology led scientists to wonder how natural temperate forests and tropical rain forests, could be so productive and prolific without any apparent external source of fertilizer. Soil fertility in these areas is marginal but stable, and yet plant growth is quite impressive.
In addition to the mycorrhizae which literally means (root fungus), various soil bacteria will proliferate in the root zone (rhizosphere).
(Mycorrhizae literally fungus root under magnification)
(Microscopic view of active rhizosphere)
(View of root hair under magnification)
Together the mycorrhizae fungi and rhizosphere bacteria as they are called, along with a host of various protozoa, nematodes , soil arthopods and worms serve to alter soil chemistry and fertility. They also serve other important functions, such as making trees more resistant to pests and disease and improving water, mineral, and nutrient absorption. The mycorrhizae fungi in particular, attach themselves to the root systems of trees and help them in the ways just mentioned by radiating outward into the soil forming an extensive network of fine hair like filaments called hyphae. A mass of hyphae is a mycelium which can develop very rapidly. A fungus colony can produce more than a kilometer of new mycelium in 24 hours thereby covering a large surface area.
(A mycellial fan or hyphae)
(mycorrhizal mycellium under magnification( 500 times)
This large area of fungal filaments, is able to penetrate the tiny spaces in the soil that are inaccessible to the actual tree root, and thus they can extract or convert certain nutrients such as nitrogen and phosphorus into soluble forms which are more easily assimilated. These nutrients are faithfully sent back to the root system. In exchange the host tree feeds the fungi with sugars , proteins, amino acids and other organic substances.
Truly it is a win win situation, think of the mycorrhizae fungi as an extended root system of the actual root system. Although this cycle of give and take imposes a cost to the host tree, it is considerably less than the cost of having to build an equivalent absorption network solely with roots.
Sustainable bio-fertility is directly dependent on the continued microbial proliferation of the soil, in and around the root systems of trees and plants. Like compounding interest the result is healthier more productive trees, and since the tree and it’s microbial neighbors in the soil are active, they reproduce and maintain themselves thereby sustaining fertility.
Some characteristics of bio-fertility are:
1. Bio-fertility is self sustaining, as long as organic material is available in the soil or from living roots.
2. Bio-fertility does not leach from the soil in significant amounts, because it is absorbed as soon as it is produced.
3. Bio-fertility does not contribute to ground water contamination.
4. Bio-fertility does not produce sudden growth spurts because it builds and accrues gradually.
5. Bio-fertility is compatible with chemical fertility.
6. Bio-fertility is created in small amounts, and is localized in the immediate root zone (rhizosphere) where it is needed.
Like air and water, the soil is a precious resource, but it is not an unchanging resource. On the contrary, the quality of the soil in any one location can change dramatically in a relatively short time. Our urban environments are a good example of this. Soils in natural undisturbed forest areas generally contain robust and diverse populations of mycorrhizal fungi. In urban areas however activities such as site development, tilling , topsoil removal, grading, digging, and soil compaction destroy many of these beneficial fungi.
Many of the top performing mycorrhizal fungi do not disperse their spores in the wind, and colonize by moving root to root in the soil or by being consumed and redeposited by their animal vectors.
In a disturbed habitat, the effectiveness of the return of mycorrhizae is largely dependent on the quality and proximity of undisturbed habitat. Many cases have been documented, where trees in disturbed urban and suburban environments have not formed mycorrhizae many years after out-planting, and are surviving only through intensive care and maintenance.
Once the secrets of sustainable bio-fertility were known, scientists began to consider ways to apply this phenomenon for agricultural and horticultural use. Over time, they began to isolate and identify various beneficial microbes that would have the desired fertility enhancing effects in the root zone, and thus bio-fertilizers were born.
(there are many different types of bio-fertilizers the example pictured combines traditional fertilizer with several types of ecto and endo mycorrhizae)
In any case these bio-fertilizers as they are called need not provide fertilizer directly. Instead they supply the micro-organisms that boost soil fertility. Usually they are blended with organic nutrients to help establish the initial fungal populations in the root zone. Unlike the rhizosphere bacteria however most mycorrhizae fungi will not utilize applied organic nutrients once they are established, and prefer organic food supplied solely by the tree. Because bio-fertilizer products contain live microbes for inoculating the soil or the roots themselves, they are often called soil or plant inoculants. Some products are made by combining traditional chemical fertilizers with bio-fertilizer inoculants, to provide an immediate boost to soil fertility in the short term as well as a sustainable fertility effect for the long term. It is an interesting fact that trees which have been treated with these microbial inoculums actually become less dependent on external sources of fertilization.
As far as traditional fertilizers go it is important to understand the nutritional needs of the particular species of tree which you will be fertilizing. Of critical importance, is the chemical analysis of the fertilizer this is identified by the 3 numbers on the bag or container, these indicate the content of nitrogen, phosphorus and potassium the 3 main elements discussed earlier.
It is also a good idea to become familiar with the chemical symbols for each of the three main elements as well as the various trace elements, these are as follows:
These are the 17 essential elements needed for proper tree growth and development. It is important to remember that timing can be a critical factor, especially when using inorganic (chemical) fertilizers. Early spring is the best time for fertilizing trees and shrubs. This is when the buds begin to swell and nutrient up-take is the greatest.
Using inorganic fertilizers when trees are dormant, can create problems by depositing excessive fertilizer salts in the root zone. These can create toxic soil conditions and cause fertilizer burn problems, and so they are best applied during active growing periods when metabolic demand is the greatest.
(Many times over-fertilization can kill beneficial soil organisms in this case worms' which serve to aerate soil and process organic matter thereby improving soil quality)
(Over fertilization can also cause severe burns on tree roots as shown here)
(Symptoms of fertilizer burn on leaves)
I prefer using slow release fertilizers. These release the fertilizer over an extended period of time, kind of like a time release vitamin. Using these fertilizers, reduces leaching and the potential for fertilizer burn problems. These fertilizers can be applied any time of year as long as adequate soil moisture is present, and in northern areas as long as the ground is not frozen. Slow release fertilizers are defined as fertilizers that contain at least 50% water insoluable nitrogen.
Another consideration when fertilizing, is application rate. This depends upon the age, health and species of tree, the form of the fertilizer, the method of application and the site conditions. The general recommendation for slow release fertilizers is 2 to 4 pounds of actual nitrogen per 1000sq ft. of root area. Quick release fertilizers should only be used when the objectives of fertilization cannot be achieved with slow released fertilizers.
Application rates for quick release fertilizers should be between 1 to 3 pounds of actual nitrogen per 1000 sq. ft. of root area, and should not exceed 4 pounds annually. To find the amount of actual nitrogen in a given bag of fertilizer, the fertilizer analysis number on the bag which represents the percentage of the three main elements in the mixture, nitrogen being the first is multiplied by the weight of the bag. For example: In a bag of 8-2-12 8% of the mixture is nitrogen if the bag weighs 50 pounds the problem is stated as such 50 x .08 = 4 hence there would be 4 pounds of actual nitrogen in the bag.
Soil PH, or the relative acidity or alkalinity of a medium also effects nutrient availability. If a soil is too acidic or alkaline, certain nutrients can become bound up or made insoluable, thereby preventing absorption. As a general rule, most trees and shrubs prefer a slightly acidic to slightly alkaline soil in the 4.8 to 7.2 range 7 being neutral.
The most accurate way to determine a trees elemental needs, is to obtain laboratory analysis of the soil and leaves. A soil analysis can provide valuable information about the presence of essential elements, soil P.H. organic matter content and cation exchange capacity, which is basically the ability of a soil to absorb and hold cations. These are positively charged ions and c.e.c. is basically a measurement of how hard plant roots have to pull to obtain water mineral nutrient content from the soil, or how tightly bonded this solution is to the soil particles. Essential elements in a water solution are absorbed through tree roots, while in solution these elements become positively charged ions called cations. Soil particles on the other hand carry negatively charged particles called anions which attract and hold cations to a higher or lower degree. The more fine textured clay a soil contains the greater its cation exchange capacity. The attraction between soil particles and cations minimizes the tendency of elements to leach or wash out of a soil. Because of this fine textured soils are usually more fertile than coarse textured soils. Bulk density is another soil quality that can be derived from a lab analysis this is basically a measurement of the dry weight of a given unit volume of soil. This is usually expressed in grams per cubic centimeter. Densities greater than 1.8 in fine textured soils such as those with a heavy clay base indicate poorly drained or compacted soils that are difficult for tree roots and water to penetrate. Bulk densities between 1.0 and 1.4 are good readings and normally indicate adequate soil conditions for optimal root growth. Higher bulk densities especially in clay soils (1.5 to 1.8) reduce root growth and subsequently tree health. Bulk density usually ranges from (1.0 to 2.0) for mineral soils.
The PH and salt content especially in arid regions are of critical importance when recommending treatments. When taking soil samples small cores should be taken from different areas of the root zone or planting area. These should be mixed together. This procedure will give results that are averaged over the entire area. A soil probe or small garden trowel can be used.
A foliar analysis is also a good idea. Analyzing dried leaf samples may help in diagnosing certain deficiencies or toxicities. A soil analysis or foliar analysis alone however can be misleading. It is possible for certain minerals to be deficient in leaves, but plentiful in soil and unavailable due to soil PH problems. These two analyses should be done together for greater accuracy. Once again this valuable service is relatively inexpensive, and can be done via the local university or county extension service as well as the dept. of agriculture division of forestry. We also provide this service to our customers and clients.
The subject of fertilization is indeed a broad one and there is not enough space here to cover every aspect. I have however tried to give you some of the basics and cover some of the key points. If you are considering having some fertilizing done, and still aren’t sure where to begin give us a call we can advise you on the best fertilizers and methods to adequately meet your particular growing needs, and can provide quality service to ensure the optimal health and longevity of all the trees and shrubs in your landscape.
(Leaving the leaves where they fall is a great way to keep the soil healthy)
( A micorrhizal root under magnification)
(Excess fertilizer salts transported by storm water run-off is one of the major causes for ground water contamination)
(Interaction between tree roots and mycorrhizae)
(There are many fertilizer manufacturers that produce chemical fertilizers with added mycorrhizal inoculants)
In the old school of thought, rapid growth was associated with a healthy tree and so the faster the growth the healthier the tree. Recent research however, has proven this assertion to be false. In fact we often encounter nursery cultivated trees, where production techniques are geared towards pushing growth, that do not perform as well once planted in the landscape.
Close examination of forest soil revealed a surprisingly different source of fertility. When we view trees, we only see the above ground portion so it is easy to overlook what is constantly happening underground. There roots occupy a soil environment that is teeming with microscopic organisms. A thimbleful of forest soil contains millions of these tiny entities. Among these many micro- organisms , are the all- important mycorrhizal fungi which form symbiotic relationships with trees and plants.