National Wildlife Federation/ San Diego County
Are Your Trees Suffering From Root Problems?
Copyrighted 2003 by Fran Lambert, Certified Arborist WE-ISA 2363
This Special Report is intended to educate tree owners about how roots function within the landscape environment, how to identify potential problems, and to explore possible solutions. We find this a fascinating and important subject and hope you will too.
Landscape trees are imported into a site with conditions very different from their natural habitat and receive care that is usually quite unlike that of their wild cousins. These often adverse conditions can result in many preventable tree disorders, pests and diseases that diminish their health and lead to an early demise. Understanding how landscape and forest trees differ will help us learn to better manage the environment we have created for our trees.
Trees growing in a natural forest ecosystem have their roots in a rich, well- aerated soil full of nutrients. The soil is blanketed with organic nutrients that provide an optimum environment for root and mineral uptake. There is a complete cycle of leaves falling, decaying, and replenishing nutrients that the tree utilizes to produce more leaves, wood and roots.
The forest floor is very aerobic and allows water & air to easily penetrate the root mass. It also contains an abundance of beneficial microorganisms that break down the decomposing leaves into the critical elements. Trees flourish under these ideal conditions and often live hundreds of years just as they have for millennia.
There is no turf on the forest floor, only a deep, rich organic layer of decayed leaves. By contrast, landscape trees are often located in lawns that rob the trees of the deep water, oxygen and nutrients they need to grow and thrive. The thicker and more well watered the lawn, the less air and water reaches the tree roots. If there is no lawn under trees, leaves are typically raked up.
Urban soils are frequently poor or compacted and are subject to big fluctuations of temperature and moisture. This can often kill tree roots or simply prevent them from growing. Trees may become hazardous when root systems fail due to damage from these factors.
Further, a wide variety of plants not normally grown together are added to our landscapes and compete with trees for resources and space. Beneficial microorganisms that naturally assist tree roots with absorption are often absent or in short supply in this artificial environment. Soil pH is altered and can disrupt fertilizer uptake, causing deficiencies. Excessive fertilization and frequent shallow irrigation often builds up salts, which draw moisture from tree roots leading to further damage or even death.
Many of our urban and suburban soils have been significantly altered by development. During excavation the top layers of the original soil are hauled away to prepare the lot. Often only a few inches of landscape mix is added and large numbers of plants installed, all trying to survive in this limited soil profile. Most of our North County coastal soils are compacted or densely structured containing little or no organic material; so all roots are forced into the area closest to the surface causing tremendous competition. Under these circumstances, trees tend to develop large surface roots that become problematic for the rest of the landscape and hardscape. Under ideal conditions, 95% of tree roots would be functioning in the top 18” of soil.
Drainage is usually poor between these layers causing roots to decay from fungi that flourish in the absence of oxygen and the continual excessive moisture. Under-utilized fertilizers also end up in this interface and create a very stagnant toxic zone. Beneficial fungi and bacteria are either non-existent or in such low populations that they are unable to enhance water & nutrient absorption or serve as a line of defense. Root pathogens and crown rot flourish and this decay can eventually lead to whole tree failure. Compaction from construction, foot traffic, over irrigation etc. restrict permeability of air and water and does not allow carbon dioxide to escape, greatly impairing tree root function. So it is no wonder that many trees fail to thrive or are suffering from various disorders and diseases in the first few years after installation or construction.
Landscape installations and improvements may not take the long-term needs of trees into account. In fact, the ecosystem that is created often works against the trees. Tree root systems extend far past the dripline. Up to 50% of the roots will eventually be located outside the zone directly under the tree. Most of the fine, absorbing roots are located within inches of the surface and require oxygen to function. Many landscapes have turf, ground cover, or ornamental plants located right up to the tree trunk and covering most of the root zone. Trees cannot compete with them for the water, nutrients and air they need, as their roots are much slower to respond. Trees then become stressed and prone to diseases, pests, decay and other disorders.
These problems are compounded by the frequent practice of attempting to achieve the “instant landscape” i.e. installing too many trees and too much plant material to live to maturity in the area allotted. Fast growing trees that will become too big for the space are put in, dooming them to an early death when they outgrow the space. This is so unfortunate because removal & replacement is costly and often upsetting. It is difficult to condone this practice when there are so many choices of trees that will grow here that fit almost any application.
Existing trees that remain on site during development or even landscape remodeling are frequently subjected to tremendous stress. Often their roots are severed, their trunks damaged, the grade is lowered or raised, construction materials are piled or poured onto their roots, and the earth around them is compacted by heavy equipment. Many times they are given little if any water during the entire construction process. Sadly many mature trees die within a few years of construction because their root zones were not addressed or adequately protected during the project. Since they are of great value to the final result, their survival may depend on a systematic effort to address potential damage and implement a long-term plan. Being proactive about trees during construction is certainly preferable to trying to remedy a tree that later goes into decline.
Trees that are growing in poor soils such as those severely disrupted by development or have been subjected to improper landscape maintenance procedures can greatly benefit from deep root care.
How do you know if you have a stressed tree?
Some signs & symptoms of a tree in decline include stunted or sparse growth, poor leaf color, nutrient deficiency, upper canopy dieback, excessive seed or cone production, early leaf color, early leaf drop, late leafing out in spring, wilt, insect infestation, and disease. All of these may well be indicators of root problems.
Trees are genetically programmed to try to survive as long as possible. So the answer to most of these problems is to re-create forest conditions as closely as we can within an artificial environment. Trees are amazingly able to recover over time, once their needs are systematically met. Arborists who understand how trees work within the landscape can partner with tree owners so that their trees will be as healthy and long-lived as possible.
These are the steps we recommend to promote healthy root systems in landscape trees. The more closely they are followed, the better and faster the results. These recommendations may be critical to the survival of stressed trees.
The first step toward tree recovery is to carefully remove turf and other competing plants growing right under the tree, making sure tree roots are not damaged or left exposed. If the plants can be taken out intact, they may usually be transplanted into a more appropriate spot. Ideally, no other plants should be growing out to the edge of the tree canopy. The more open the area, the healthier the tree. Soil piled up over the trunk of the tree may be removed in some cases.
Second, a means of providing aeration, water and nutrients to the top 18” of soil should be installed if the soil is dense or impervious. Vertical mulching, a technique that opens up holes in a prescribed manner within a tree’s root zone, can solve many tree problems simultaneously. Usually these holes are backfilled with various materials. This simple process will help provide a higher soil oxygen level and allow carbon dioxide, methane and other gases to escape, much like in the forest.
Installation of special aeration tubes at the time of vertical mulching can have far greater benefits as they will remain open over time and be reused over and over for irrigation and fertilization. Oxygen, water and nutrients can be continually available to the tree roots with this system. They allow tree roots to grow deeper and be less competitive with the roots of other plants & turf. Equally important, vertical mulching tubes make it possible to water trees separately from the rest of the plants. Trees require infrequent, deep irrigation and these root aeration tubes provide a means for much needed moisture to reach the tree roots at the proper intervals. The aeration tubes can also be used to leach undesirable substances out of the root zone.
One type of root aeration tubes can be attached to an irrigation system while the other can work independently. It can also be used with drip irrigation or a soaker hose. As trees mature, it is recommended that additional vertical mulching and/ or aeration tubes be extended further out into the root zone. This can be evaluated during an arborist’s annual review of the trees.
It is best to have a knowledgeable arborist install vertical mulching to ensure that woody tree roots are not damaged in the process and that aeration holes are properly spaced based on site conditions.
Third, a thin layer of composted organic mulch should be applied to as much of the tree root zone as practical. This will create a more natural environment and improve tree health. Properly installed mulch can help maintain soil moisture and temperature. It will also improve aeration, structure and fertility over time. Mulch helps control weeds and can serve as a natural form of pest control as well as inhibiting certain plant diseases.
Mulch is also very pleasing aesthetically. A plant border of perennial and annual flowers can be installed between the mulch and turf to soften the look, if desired. The mulch will allow the fine, absorbing roots located within inches of the surface to receive adequate moisture, oxygen and nutrients. It should be re-applied annually to maintain the ideal depth of 2”-3”.
Great care should be taken not to apply mulch right next to the tree trunk or the root crown can be suffocated, causing dysfunction or decay. Overly deep mulch prevents oxygen and water penetration and should be avoided. It can cause serious problems such as toxicity, diseases, deficiencies, overheating and suffocation of the root zone. Always supervise mulch distribution to avoid these common errors or have it applied by a professional arborist. Landscape gardeners are usually not aware of these guidelines. It is also advisable to use composted mulch that has been thermophilically processed to eliminate pathogens, especially for trees in poor health. Cultivate into soil for best results.
Fourth, trees that have been growing in less than ideal conditions or are in decline can benefit from the proper application of fertilizer and other soil additives. Usually trees receive only the high nitrogen fertilizers commonly applied to turf and ornamental plants. This often causes excessive weak growth that can attract pests and require much more frequent pruning than a tree receiving proper nutrients according to seasonal needs.
The natural inclination of many people faced with a declining tree is to give it a big dose of fertilizer. But fertilizer alone will not cure a tree that is showing signs of environmental stress. What may appear as a nutrient problem or even a disease may instead be a symptom of an abiotic disorder. These include soil compaction, poor aeration, improper irrigation, excessive salt buildup, herbicide damage, pH problems and a host of other difficulties. A word of caution: avoid applying nitrogen to stressed trees or they will use up all their energy reserves pushing new growth. Consult an arborist if in doubt.
The timing of fertilization is important. There are also specific formulations that should be applied each season if a qualified professional, preferably an arborist, identifies a need for fertilization. Spring fertilization will encourage tip and leaf growth. Summer fertilization promotes wood production, while fall fertilization develops roots. In very damaged trees, it may be advisable to wait on fertilizing until the tree shows some signs of recovery. Then apply a low nitrogen product.
The best way to fertilize trees is a combination of surface and deep root applications; vertical mulching tubes are ideal for this. Fertilizer should not be applied near the trunk but rather at the dripline and beyond. This will encourage proper tree growth rates and patterns, which results lower maintenance requirements and fewer problems. By the way, trees are fertilized, not fed, as they make their own food when the right conditions are present.
Beneficial living organisms (such as mycorrhizae) that form symbiotic relationships with tree roots and serve as an extension of the root system are often missing from poorly functioning soils. Stressed trees may benefit from introducing mycorrhizal inoculants and other soil additives through vertical mulching tubes or injections into the root zone. For best results, a qualified professional such as an arborist should apply these specialized materials.
Fifth, all trees should be inspected annually to identify pruning needs, inspect the root zone and provide any needed intervention or fertilization. Some arborists offer an annual service package that includes this preventative maintenance. It is also wise to monitor your own trees monthly for any changes.
Healthy trees with strong, well developed and fully functioning root systems will be better able to resist and recover from any stressors, whether caused by nature or introduced by man. A systematic deep root care program can pay for itself many times over.
Your trees deserve the best care you can provide both above and below ground. They will reward you with many years of beauty and enjoyment. Investing in their care will save you time, money and concern in the long run. They will be far less likely to fail in storms or succumb to the latest pest or disease, and be more able to recover from past damage. Mature specimen trees also add great value and beauty to your property.
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