Issue: May 8, 2004

Mesquite tree and septic system


I saw your column in the Las Cruces Sun-News. My husband and I are new to this area, having moved here one month ago. My question to you is this: There are two mesquite trees that have been planted in the front yard. Each tree is about 10-feet tall and not on a drip system. However, they are planted in between three 60-foot drain lines to our septic system. (The house we bought is 14 years old.) Should these trees be removed? We certainly do not want the trees to ruin our septic field.

E. L.

Las Cruces, NM


This is a difficult question to answer because there are a lot of factors to consider and because plants don't always do what they could do. It is possible there will be no problem, but there is the potential for problems in some situations.

You stated that the trees are near the lines to the septic tank. These should be heavy plastic lines with glue joints that prevent leakage. The only concern in this case is if the pipes cracked for some reason. If so, the water leaking from the cracks would encourage root proliferation, and there is a chance that the roots will enter the pipe and cause clogging.

When you mentioned that there were three lines, I wondered if these were the "leach" lines going from the septic tank. In this case, the possibility of problems is greatly increased. The purpose of leach lines is to allow the liquid effluent from the septic tank to infiltrate the soil. This creates a very hospitable environment for roots. Roots cannot grow in dry soil but where there is moisture, their growth is abundant. Where the roots grow vigorously, there is the potential for them to enter into the perforated septic lines and create problems. In some parts of the country, the pipes must be buried deeply to avoid freeze problems, reducing the potential for problems. In Las Cruces, the depth need not be that great. The mesquite is a tree with the ability to root to great depths. These two factors combined suggest that the potential for damage is great.

It is not clear how long the trees have been there. From their size, I suspect they are fairly new. If they have been there for many years without causing problems, then I would leave them in place. On the other hand, if they are fairly new, they may be just now reaching the point where they can cause problems. In that case removal and replacement with something less likely to cause problems (probably not a tree) is the best course of action.

The decision is yours to make. However, if you need some additional help, contact your local Cooperative Extension Service office for an on-site determination. Your County Extension Agent or Master Gardeners associated with the office will be able to give advice based on what they see on your property.

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Yard and Garden, ATTN: Dr. Curtis Smith

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9301 Indian School Road, NE, Suite 112

Albuquerque, NM 87112

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. New Mexico State University is an equal opportunity/affirmative action employer and educator.