By: Bill Reichenbach, Certified Arborist WI-0188A
When thinking about trees and tree health, we should be more aware of what is below ground. Healthy root systems are vital to the health and longevity of trees. A vigorous expanding root system is supported by healthy soils. Often times when the trees crown appears stressed - thin canopy, small or chlorotic leaves, branch dieback - it is the root system and corresponding soils that are the real issue.
Roots obtain water, and essential elements from the soil. Abundant oxygen in the soil is critical for respiration. A good root system anchors the tree in place. Roots also store carbohydrates for growth and tree defense.
The majority of a trees root system is in the top 6 to 24 inches of the soil. They occupy an area two to four times the diameter of the trees crown if there is room. Root systems consist of large woody roots and many smaller non-woody ‘feeder roots’. These small feeder roots constitute the major portion of the root systems surface area.
What are some of the common factors that cause root problems and tree stress?
-Nutrient poor, compacted, alkaline soils with low organic matter content. Many soils in our landscapes have been disturbed in the building process. Topsoil has been striped away and sub soils have been brought to the surface, often rubble or limestone building materials are mixed in the surface layers. Heavy equipment and even continued foot traffic compacts soils limiting oxygen in the soil and increasing run off rainfall. An ideal soil for most trees in our area is a nutrient rich, loose well - drained soil with plenty of organic matter. Unfortunately, that is not the typical situation.
-Competition from turf grass. The root systems of lawn grasses strongly compete with shallow tree roots for nutrients and moisture. Grasses even produce chemicals that restrict the growth of other plants.
-Physical damage to roots. This often happens in the construction process. Heavy equipment, changing of grades – cuts or fills will compact soils, physically remove roots or create wounds that allow the entry of fungal disease pathogens. Even lawn mower blades can damage the surface woody roots.
-No recycling of nutrients. In many landscape’s, leaves in the fall are removed from under the trees. In the natural forest, this material is deposited on the forest floor to decompose. This allows for the recycling of nutrients and build up of organic matter, which is so important in developing healthy soils and root systems.
-Drought or over watering. Extended drought is an obvious problem – especially for the fine feeder roots. Fine roots will die under extreme dryness. The tree will grow new roots when good moisture conditions return but at the expense of stored food reserves. Excess moisture, with resulting oxygen depletion in the soil will have the same impact. Mismanagement of irrigation systems can be the culprit.
What should be done to lessen these problems?
-Mulch Mulch Mulch – Using shredded bark or wood chip mulch is one of the most beneficial procedures we can do to trees to improve soil, roots and over all tree health. Mulching simulates the natural forest floor environment. It eliminates grass competition, helps retain soil moisture, increases soil fertility, and improves soil structure and organic matter content. It also protects the trunk and the buttress root system from string trimmers and lawn mower damage. Improper mulching can be harmful. Do not pile mulch up upon trunks. Keep mulch a few inches away from tree trunks. A 3-4” thick layer of mulch is ideal, the larger the area the better. Root systems are expansive; we want to mulch as much of the soil and root system as is practical and aesthetically pleasing. Less competitive plants, low shrubs, perennials and ground covers will enhance the appearance of mulch beds. Native plants often work well emulating the natural forest floors found in our Wisconsin woodlands.
-Fertilization and root biostimulants are most effective to improve nutrient availability and tree vigor. Turf grass robs much of the available nutrients in most landscape settings and the lack of recycled leaf litter limits available nutrients. Fertilization will provide needed supplemental nutrients. High quality slow release products are best.
-Compost and compost teas add life to soils. Compost applied to the soil surface as a mulch or prior to mulching greatly improves soil structure and moisture holding capacity. It also greatly enhances beneficial soil microorganisms improving soils and root health. Compost teas also provide much needed ‘life’ to poor soils.
-Mycorrhizae soil inoculations add beneficial fungi often limited in landscape soils. Mycorrhizae (meaning fungal root) are a critical component of healthy tree roots. These fungi actually increase the uptake of nutrients and moisture and improve disease resistance.
-Vertical mulching or air spading of severely compacted soils. Alleviating severe compaction will greatly improve tree root function. The addition of compost and/or mulch after this procedure will have long lasting beneficial impact.
-Proper watering during dry periods. Trees need, on average one inch of water every seven to ten days. Frequent, shallow watering does not properly meet the needs of either trees or turf. Over watering can, be just as harmful as lack of moisture.
The season is upon us. Spring is here. Now is the time for your Wachtel Certified Arborist to visit your property, to observe your trees, and discuss with you a plan to improve your trees from the ground up!