Landscaping the ground over a septic system beautifies a less-than-inspiring view but choose plants with care. Certain trees and shrubs can cause damage with their aggressive roots when planted around septic tanks and drain fields. Learn which plants are the worst to grow over a septic system and which are safer choices.
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Safe Plants to Grow Over Septic Tanks and Drain Fields
Don't become so paranoid about the potential of root damage on a septic system that you abstain from planting anything in that area. You just need to know some best practices for how to landscape a septic tank and drain field. Growing the right kind of vegetation here is not only permissible but actually advisable. Plants can help to prevent erosion and suck up excess moisture from the drain field.
As for what you can plant over your septic tank and drain field, grasses (including ornamental grasses) often work best. Their shallow root systems are less likely to invade the septic system and cause damage. For the same reason, small, non-woody ground covers are a good choice. Here are some options to consider:
- Tall fescue grass
- Kentucky bluegrass
- Creeping Charlie
If you're insistent on growing trees and shrubs around your septic system, shallow-rooted kinds are best. Options include: dogwoods, Japanese maples, Eastern redbuds, cherry trees, hydrangeas, azaleas, boxwoods, holly, and dwarf tree varieties.
A good way to narrow down plant options is to consider these tips:
- If the area is sunny, consider perennials for sunlit areas.
- If the spot does not get much sun, look at shade garden plants.
- The soil around septic systems is sometimes wetter than average, sometimes saltier than average, and sometimes both. Cover both bases with perennials, such as bee balm, hollyhocks, and wild violets, that tolerate both wet ground and salt.
- Deer will still eat plants growing over septic systems. So if you have a high deer population, look into deer-resistant perennials, ground covers, bulbs, and grasses.
The Worst Plants to Grow Over Septic Systems
Avoid planting large, fast-growing trees over your septic system. In addition, some of the worst offenders when it comes to septic damage are trees and shrubs with root systems that aggressively seek out sources of water. They aren't fussy about the water source they tap into, meaning the pipes in your septic tank drain field are very much fair game.
Here are some common trees and shrubs to avoid growing over a septic system:
- Pussy willows
- Japanese willows
- Weeping willows
- Aspen trees
- Lombardy poplars
- Birch trees
- Beech trees
- Elm trees
- Most maple trees other than the Japanese maple
- American sweetgum trees
- Ash trees
- Tulip trees
Some gardeners also might wonder whether they can put a vegetable garden over a septic field. That is not ideal. It's not safe to eat food crops grown in the ground around a drain field due to the risk of bacteria in the area.
Even if you've avoided growing problematic plants directly over your septic system, you're not in the clear. The roots of large, mature trees nearby can pose a risk. The general rule is a tree needs to be at least as many feet away from your septic drain field as it is tall. So a specimen 50 feet tall at maturity should stand at least 50 feet away. Failing that, it is possible to install root barriers to try to keep tree roots from invading your septic drain field (similar to the bamboo barriers used in controlling invasive bamboo).
The Basics of How Septic Systems Work
In areas that lack sewer systems, septic systems serve as wastewater treatment facilities. A pipe brings the wastewater from the toilets, showers, sinks, and washing machine out of your home and stores it in the septic tank, which is an underground, watertight receptacle.
The septic tank is designed so that solids ("sludge") and scum will separate from liquids. The solids sink to the bottom. The scum rises to the top. The liquids form a middle layer in between the scum and the sludge.
The liquids eventually exit via a T-shaped baffle pipe. The catalyst for their exit is the entry of additional wastewater from the house. The ingenious baffle is designed so that only the liquids can exit through the pipe. Their discharge takes the liquids into a much larger part of the septic system known as the "drain field" or "leach field."
The drain field typically consists of a number of perforated PVC pipes laid in underground trenches. The trenches are filled with crushed stone or gravel. They may be covered with drain field fabric to keep dirt out.
Because the pipes are perforated, they allow wastewater to exit into first the crushed stone or gravel and then the soil below. The wastewater is said to "percolate" through the ground. This process removes most of the harmful bacteria present before it can reach groundwater. Excess moisture in the soil will be taken care of through evaporation unless you (mistakenly) do something to impede it.
At some point (often about three years), you must pay a septic service to pump the sludge and the scum out of the septic tank.
Planning a Septic Field Garden
It is primarily the drain field pipes that you have to worry about when planting around septic tanks. You do not want roots penetrating the perforations and gumming up the works. All of the parts of this carefully tuned system must be functioning properly or else the result is a mess (and a costly one).
You can plant flowers on a septic bed, as they are sufficiently shallow-rooted. But it's best to choose perennials over annuals. The less gardening work you have to do in a septic system area, the better—both for you and for the septic system. Always wear gloves when digging in a drain field to protect yourself. And never dig deeply, as you could damage the system.
In addition, avoid the following, which can interfere with the normal evaporation process that removes excess moisture:
- Adding soil to the area
- Mulching too heavily
- Watering the plants more than you absolutely have to
When you select low-maintenance plants that are suitable for the environment, you can sit back and enjoy the greenery without having to worry about your septic system.
Planting On Your Septic Drain Field. Virginia Tech Cooperative Extension
The Effect of Soil on Human Health: An Overview. European Journal of Soil Science.