Tree Root Growth Gone Wrong

Surface roots can pose a major hazard. Photo: John C. Fech

Like most important things in life, roots can grow well, poorly or somewhere in between. When tree roots don’t develop properly, the consequences can affect people, property and the tree itself. Little can be done to improve a poor root system, so it’s important to do what you can to ensure a healthy root system, as well as be able to recognize when a tree’s root system is unhealthy and in need of care.

Surface roots are a common issue that is hard to deal with. Photo: John C. Fech, UNL

Surface roots are a common issue that is hard to deal with. Photo: John C. Fech, UNL

Fostering good roots

Perhaps the best way to start consideration of the bad is with the good. Picture a bicycle wheel turned on its side, with the center hub representing the trunk and the spokes representing the roots. Roots are supposed to look like spokes of a bicycle wheel, but a few sinker or spiker roots are also produced, especially early in the tree’s life. In general, the radicle, the first root, is produced and oriented straight down, with the following roots growing horizontally.

Avoiding bad roots

The most effective way to prevent bad root system development is to plant trees properly in suitable locations and follow up with good maintenance. Finding the right place for a tree includes an understanding of site conditions, including hours of direct sun received, soil texture, soil structure, slope and soil moisture conditions.

As each root adds a new layer of growth, it becomes greater in diameter, just like the trunk. This occurrence is a powerful force. Photo: John C. Fech, UNL

As each root adds a new layer of growth, it becomes greater in diameter, just like the trunk. This occurrence is a powerful force. Photo: John C. Fech, UNL

Balled and burlapped (B&B) trees typically lose a substantial amount of their root system while being dug from growing fields. This root loss can create significant stress on the tree during drought conditions and can limit plant vigor and establishment. Potted tree root systems are intact when planted, but circling roots within the container can lead to future defects if not corrected or removed. Bag or fabric containers are designed to limit circling roots and typically provide a vigorous and fibrous root system that maximizes initial tree establishment in dry conditions. Take special care with bare root trees, since the roots can dry quickly when exposed. The benefit of the exposed root system is that it allows for pruning of dead and damaged roots and proper root spread at planting.

Digging an adequately sized planting area will help loosen the surrounding soil and support stronger root establishment during periods of drought. Try to avoid disturbing the soil in the bottom of the hole or settling may cause the tree to end up deeper than intended. Compost shouldn’t be added to the backfill when planting the tree, but it can be used to topdress around the tree and out to where roots will grow in the future. Wood chip mulch can also be used for this purpose.

Root rot in the bole reduces structural integrity. Photo credit: John C. Fech, UNL

Root rot in the bole reduces structural integrity.
Photo credit: John C. Fech, UNL

To properly plant, place the root mass in the hole at the appropriate depth and begin filling the hole with soil. When the hole is approximately one-third full, gently replace and settle the soil around the root mass. Then continue to fill the hole, stopping every few inches to settle the soil with water. Ensuring good soil-to-root contact will help the tree maximize water uptake during dry conditions.

Chronic mechanical damage from lawn mowers, string trimmers and other motorized equipment causes long-term damage to trees that can compromise their health, predispose them to insect and disease problems, and ultimately reduce a tree’s life span. This damage can be minimized by separating the lawn from trees with a mulch ring.

Mulch should be organic material that breaks down to enhance nutrient cycling and soil porosity. It should be spread in a flat layer 3 to 4 inches deep outward from the trunk, ideally extending outward to the tree drip line. Mulch should never be piled against the bark to any depth; buried bark remains wet and has an increased potential for disease and damage. Excessive quantities of mulch can stifle gas exchange and water infiltration into the soil and also stimulate root growth in conditions that are only temporarily favorable once the mulch dries out again.

Surface roots are a common issue that is hard to deal with. Photo: John C. Fech, UNL

Surface roots are a common issue that is hard to deal with. Photo: John C. Fech, UNL

Amiss roots

If proper planting procedures and maintenance guidelines aren’t followed, tree roots can grow in an unhealthy manner and produce undesirable results. These results can be manifested in several ways.

Most of my clients are well aware of the “each year a tree adds another ring of growth” concept as it applies to the trunk. However, few of them realize this process also occurs in the roots. As each root adds a new layer of growth, it becomes greater in diameter, just like the trunk. This occurrence is a powerful force, and in some cases strong enough to heave up driveways and sidewalks.

Poor placement and tree tendencies often lead to roots raising concrete. Photo: John C. Fech, UNL

Poor placement and tree tendencies often lead to roots raising concrete. Photo: John C. Fech, UNL

Stem girdling roots are often the result of failure to inspect the root mass at planting time. Often, roots are already beginning to circle in the container and simply continue to grow in that fashion as the tree grows. Sometimes roots grow in a relatively loose potting medium and are planted into denser landscape soils. In these cases, the roots have difficulty both growing out of the original root mass and penetrating the landscape soil. As a result, the roots turn and grow back into the potting medium, eventually girdling the tree.

Whether “large and getting larger” or stem girdling, roots that are problematic in these ways can sometimes be detected through a little excavation. If you’re using a simple hand tool for the process, such as a sod spade or camp shovel, be careful not to injure roots. An air spade, though more invasive and expensive, is another option for this task. No matter which tool you use, a little digging can tell a lot and help you discover possible causal agents.

Cutting through roots during other landscape operations can create several problems. In some cases the cut root will branch out and produce more roots in a similar fashion to the subsequent growth that is produced following the shearing of a hedge. In others, the freshly cut surface is subject to various invading fungi that cause the root to soften and rot, leading to a decline in water and nutrient transport, as well as structural support for the tree.

When root rot is introduced into tree roots, the tissues can simply soften and slowly decompose, resulting in minimal consequences. However, if the tree species is a poor compartmentalizer, the decay can spread slowly and surely into the entire bole, causing a significant weakness in the tree’s stability. When this occurs, the tree may fail catastrophically, causing harm to people and property.

Stem girdling roots cause damage by impeding the uptake of water and nutrients. Photo: John C. Fech, UNL

Stem girdling roots cause damage by impeding the uptake of water and nutrients. Photo: John C. Fech, UNL

Some tree species have a tendency to produce surface roots, while others don’t. Maples, cottonwood, poplars and bald cypress are among those trees with strong surface rooting tendencies. Species characteristics are not the only influential force in the expression of surface rooting. Repeated water movements, hardscape restrictions and hardpan soils can also cause significant expression of exposed roots. Surface roots are not only objectionable to arborists and clients, but they also pose a trip hazard.

The perennial question from clients regarding surface roots is “What can I do?” Unfortunately, there is no one all-encompassing answer. Possible solutions include shoehorning low-growing perennials and ground covers amongst the roots, creating a new landscape bed that no longer needs traditional lawn maintenance, and placing wood chip mulch between the surface roots in a manner that replicates what occurs in a naturalized setting. In either case, it’s wise to avoid placement of topsoil over the roots, as this keeps them moister than normal and greatly reduces oxygen exchange, both of which discourage healthy root growth.

Tips for Proper Root Maintenance

  • Plant trees properly in suitable locations and remember to follow up.
  • Take special care with bare root trees, since the roots can dry quickly when exposed.
  • Digging a good-sized planting area helps loosen the surrounding soil and supports stronger root establishment.
  • Compost or wood chip mulch can be used to topdress around the tree and out to where roots will grow in the future.
  • Ensuring good soil-to-root contact will help the tree maximize water uptake.
  • To avoid root damage from motorized equipment, separate the tree from the lawn with a mulch ring.
  • Avoid excessive quantities of mulch; too much can stifle gas exchange and water infiltration into the soil.
  • Inspect and check all roots prior to planting.
  • When excavating roots with a hand tool, be careful not to damage the roots.
  • Avoid placement of topsoil over roots.

Read more: Guide to Protecting Tree Roots

Editor’s note: This article was originally published November 2014 and has been updated.

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