QuestionI'd like to have large trees in my backyard. Because the septic system is in the backyard, I need to know if the root system of Birches will seek out and destroy my septic system the way I have been told Maples will. Also, how prevelant are bronze birch borers in East Tennessee and should I be worried about that? What type of Birch would best suited to a northwest exposure and high clay soil content? Any help would be appreciated.
AnswerIn general, shallow-rooted herbaceous plants that are not excessively water-loving are best. A leach field is a series of relatively shallow (a minimum of 6 inches below the surface) underground perforated pipes set in gravel trenches that allow septic tank effluent to drain over a large area. As the effluent seeps into the ground, it is purified by the soil. Plant roots can help remove excess moisture and nutrients thereby making the purification of the remaining effluent more efficient. However, roots that clog or disrupt the pipes will seriously damage the drainage field. The challenge of leach field gardening is to find plants that will meet your landscape needs but not clog the drain pipes.
Trees and shrubs are much riskier choices for the drainage field than herbaceous plants. The woody roots of these plants are more likely to clog and damage drain lines. Especially notorious for line clogging are water-loving trees such as Beeches, Birches, Elms, Poplars, Red Maple, Silver Maple, Willows, Fagus spp. ,Betula spp.,Ulmus spp.
Populus spp.,Acer rubrum, Acer saccharinum, Salix spp. willows and poplars . Do not plant these near a leach field unless you are prepared mentally and financially for the possibility of needing to install a new field sometime in the future. If you insist on growing them near a field, at least plant them at the far end where the lines will be drier and less conducive to root growth.
Some smaller and less-aggressive woody species may be suitable for planting over the drain field. Some possibilities include fibrous rooted shrubs such as boxwood or holly, or small trees such as dogwoods. When planting shrubs in a leach field, place them between the lines when possible. Normally, drainage trenches are 3 feet wide with 6 feet between trenches.
Finally, you must decide what is more important to you - the leach lines or the plants. One gardener decided that the cost of a new system was inconsequential when compared to the enjoyment and shade she would get from an established grove of silver maples near her leach field. It is impossible to predict how long it will take for roots to disrupt a leach field because every situation is different. The field could need replacing in as few as 8 years, or as many as 40.
Plant trees as far away as possible from the drain field. If you want to be absolutely certain that tree roots will not intrude into your drain field, trees should be planted at least as far away as their estimated root spread at maturity. One way to estimate this is by the ultimate height of the mature tree. For example, a weeping cherry may be expected to grow about 25 feet tall, and should be planted a minimum of 25 feet away from the drain field. An oak might need to be planted 60 or 70 feet away. On the other hand, if you are willing to risk some root intrusion, you may plant these non-aggressive species quite a bit closer to the drain field (although closer than 10 feet is not recommended). Although the root spread of these trees may eventually encompass part of the drain field, the roots are not likely to cause serious damage.
Prepare the soil for your trees before planting. Roots tend to grow along impermeable surfaces until they find a crack or other "path of least resistance" where they can penetrate. If you plant a tree in shallow topsoil over a compacted subsoil - a common situation in newer housing developments - the first "crack" or "path" in the soil that a tree root encounters may be your drainage field trench. Dig up as wide an area as possible for your new tree before planting to provide a good rooting environment. Prepare the soil especially well on the side of the plants that faces away from the drain field. This is where you want the most roots to grow. If you are planting between drain lines, be careful to avoid the lines and trenches. If the soil is very poor or compacted, consider amending it with organic matter (compost, leaves, peat moss, etc.). Never amend just the planting hole backfill - you should instead till organic material into the entire planting bed or at least into an area several times the size of the planting hole. Good soil preparation can help discourage roots from clogging your drain pipes because tree roots will be better able to take up adequate water and nutrients without invading the leach field.
Consider using root barriers. Another effective, although expensive, technique that may be worth trying is installing a root barrier between your drainage field and tree plantings. Geotextiles, impregnated with a long-lasting herbicide that moves only a short distance in the soil, have been used successfully to restrict root growth in street tree plantings. To effectively stop tree roots, the barrier should extend from the soil surface to a depth of at least 2 feet. Some roots may still grow under the barrier, but intrusion into the drain field should be greatly reduced. Install the barrier fabric at least 3 feet from the drain field so as not to disrupt the system. Allow at least 5 feet (the more the better) between the tree and the root barrier - more if it will be a very large tree. Finally, never encircle the tree with the barrier material; this could effectively containerize your tree and prevent it from thriving. Instead, run the material the entire length of the drain field to prevent roots from getting into the field by going around the barrier.
Bronze birch borers in East Tennessee can be a problem with white, paper and yellow birch. River birch seems to be resistant to attack. Here is a web site that lists the birches and their susceptibility to bronze birch borer.
http://www.extension.umn.edu/distribution/horticulture/DG1417.html
In the forest, birch trees thrive on cool, moist soils. Their very shallow root system makes them sensitive to even short periods of drought or heating of the soil, thus they grow poorly on hot, dry soils. Therefore, homeowners should attempt to place birch trees in locations where the soil will be shaded, cool, and moist. However, birch trees require full to partial sunshine on their leaves to grow well. The challenge is to select a growing site where the soil will remain cool and moist, but where the tree will also receive full sunshine on its leaves for much of the day.
Excellent locations for placement of birch trees in the landscape generally are found on the east and north sides of a home where the building provides afternoon shade . Avoid southern and western exposures where the afternoon sun heats and dries the soil. There are other tree species available that are well adapted to hot, dry locations. Remember that existing trees and structures can often provide the necessary shading. An excellent time to evaluate your landscape for a proper site would be mid to late afternoon. At that time, look for locations where the ground is shaded.
In the forest, birch trees thrive on cool, moist soils. Their very shallow root system makes them sensitive to even short periods of drought or heating of the soil, thus they grow poorly on hot, dry soils. Therefore, homeowners should attempt to place birch trees in locations where the soil will be shaded, cool, and moist. However, birch trees require full to partial sunshine on their leaves to grow well. The challenge is to select a growing site where the soil will remain cool and moist, but where the tree will also receive full sunshine on its leaves for much of the day.
Excellent locations for placement of birch trees in the landscape generally are found on the east and north sides of a home where the building provides afternoon shade (Figure 1). Avoid southern and western exposures where the afternoon sun heats and dries the soil. There are other tree species available that are well adapted to hot, dry locations. Remember that existing trees and structures can often provide the necessary shading. An excellent time to evaluate your landscape for a proper site would be mid to late afternoon. At that time, look for locations where the ground is shaded.
Most birch trees prefer moist but not wet soils. If your planting location is in an area that is poorly drained or that may occasionally flood for short periods of time, you should limit your selection to river or Heritage river birch both of these can also be grown on drier soils).
