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Recently, on a private growers forum I belong to, the question of growing plants over the septic tank and disposal field was asked. The member was asking if it was a good idea to use the heat from the septic tank to help with rooting hardwood cuttings. They also asked about building misting beds and grow beds over the disposal field.

Using the heat from the septic tank is a great idea. Professional plant propagators use bottom heat with hardwood cuttings to help stimulate callusing and root growth. why not use the free heat from the septic tank?

The other question is something else entirely however. My response raised a few hackles. Let’s see if you agree or disagree with my responses, and the response I received:

My response to the original question:

Annuals/Perennials…yes. Trees/shrubs…NO

Do not ever plant trees or shrubs over, or near the field. Annuals and Perennials are ok because the shallow roots will not penetrate into the field, but the trees and shrubs, if left for too long, will start to infiltrate the field and eventually block it. Then, you will need to dig up the field to fix it, which means removing those trees and shrubs anyway.
Even planting them “temporarily” may have an effect. If the roots begin to infiltrate the field, and you dig it out, you may be leaving the roots still in the field. Also, most fields are fairly shallow…2 feet or so, because the field needs to breath. Well, not actually breath, but it needs oxygen to work correctly. Personally, I would be a bit nervous about digging down into my field.

I don’t have an opinion about the mist beds on the field, but I wonder if the field will be able to “breathe” with them on it. For a definite answer on what can be put over a field, contact your State department that handles Subsurface Wastewater Disposal Systems (a fancy term for the septic systems and disposal field), or local plumbing inspector.

The response to my answer:

My nursery was over my septic tank and leach fields and we had no problems. Dwayne says no for trees and shrubs, but I wonder why he says that. My inspectors never said a word, and I’m not sure why they would. The health dept., if that’s who regulates your septic inspections, might have an issue with it if they feel it could interfere with the operation of your septic system, but worst case scenario mist in flats. Then they would be portable.

I really don’t see why it should be an issue.

I replied with:

It’s the roots

As I mentioned in my other response, it is the roots that will make the disposal field fail. The cuttings would be fine, if they are removed after a year or two, but for grow beds, it probably wouldn’t be. Some of the liners I have dug up had quite a root system to them, and that was just after 2 years, I can’t imagine the root system if they were left as stock plants for an extended period of time.

I am currently coordinating a complete septic/disposal field replacement at my full time job. The Designer, Code Officer, Installer, and the State Inspector all told me to not let any tree or shrub be planted near the system. Shallow rooted annuals and perennials are fine, but not trees and shrubs. Those trees and shrubs love that “rich” water. They all warned that the disposal field should not be driven over or compacted in any way because the bacteria need to breathe. The compaction also changes the soil composition, which affects how the soil drains.

I figured I would mention it seeing how I am currently involved with replacing 3 current systems that all had trees and shrubs planted around, over, and through them, not to mention the parking that was allowed for the past 5 years.

An “investigation” of one of the systems revealed huge roots throughout the field, (even the field that had the closest tree about 40 feet away has roots!) and severe compaction of the soil because of the parking. The new disposal field now has to be raised 2 feet because of the compaction…that will be a nice mound in the center of the lawn when it’s done!

Just passing along information I recently received that may save the field.

Now, I don’t know about you, but after witnessing the root penetration in the disposal fields I am having replaced, I personally will never plant a tree or shrub close to my own disposal field. Shallow rooted annuals and perennials are one thing, but deep rooted trees and shrubs do not belong anywhere near a disposal field. I have dug up 2 year old Forsythia liners and 2 year old Weigela liners that has huge root systems. Those small shrubs had roots that were a foot deep, and that was just two years of growing! Disturbing the cover of a disposal field is just asking for trouble. Digging into the contaminated soil could spread diseases. No thanks, I’ll pass.

Replacing a disposal field because of badly placed landscape plants is completely avoidable with just a little forethought. Save yourself some headaches and a boatload of cash, and plant your trees and shrubs away from your disposal field.

What do you think? Would you plant trees and shrubs on or around your disposal field?

For more info on planting over septic tanks and disposal fields, visit these links:

Inspectapedia-Guide to planting over septic system components

Planting on septic leach fields

Or grab this book from Amazon.com:

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