Can You Put a Raised Garden Bed on a Leach Field?


Raised garden beds offer gardeners an excellent way to garden with less effort since they are easy to maintain, improve soil drainage and aeration, and prevent soil compaction. The soil in a raised garden bed warms up faster in the spring, giving you a jump start on your gardening season. But can you put a raised garden bed on a leach field?

You can’t put a raised garden bed on a leach field as the added soil depth inhibits evaporation and limits the septic system’s effectiveness. The soil in a raised garden bed holds more moisture, which can saturate the leach field and cause it to fail. The roots can also penetrate and clog the pipes.

However, if you have limited space and must put your raised garden bed on or near your leach field, there are some things you can do to reduce the risk of damaging your septic system. In this comprehensive guide, I’ll explain the dangers of putting a raised garden bed on a leach field, how to build a raised garden bed on a leach field, and tips for gardening with a raised bed on a leach field. Buckle up, and let’s take a closer look!

Dangers of Putting a Raised Garden Bed on a Leach Field

A leach field is a critical part of your septic system. It is the final step in the sewage treatment process, where effluent from the septic tank is slowly released into the soil. It typically consists of a series of perforated pipes buried in gravel-filled trenches. The effluent from the septic tank seeps out of the pipes and is distributed evenly through the gravel. The soil then filters the effluent, removing bacteria and other contaminants.

Putting a raised garden bed on a leach field can damage the system in several ways:

Inhibits Evaporation

A septic system relies on evaporation to remove water from the effluent. As the water evaporates, the solid waste is left behind in the leach field. Unfortunately, the added soil depth in a raised garden bed inhibits evaporation, which can saturate the leach field and cause it to fail.

With the leach field saturated, evaporation can no longer occur, and the solid waste builds up. When this happens, the effluent can back up into your home through the drains, resulting in a messy and costly sewage backup.

Limits the Septic System’s Effectiveness

The added soil depth in a raised garden bed also limits the septic system’s effectiveness. The soil in a raised garden bed holds more moisture, preventing the effluent from seeping out the pipes and into the gravel. This can cause the effluent to back up into the septic tank, leading to a sewage backup.

A properly functioning leach field needs proper aeration to work effectively. With the extra weight of the soil, the leach field can become compacted, preventing aeration and further limiting the system’s effectiveness.

Roots of Plants Can Clog the Leach Pipes

A leach field typically has a series of perforated pipes buried in gravel-filled trenches where the effluent from the septic tank seeps out and is distributed evenly through the gravel. As the plants in your raised garden bed grow, their roots can break and penetrate the leach pipes, causing clogging and blockage.

If the leach pipes become blocked, effluent can back up into the septic tank and eventually into your home, leading to messy and costly sewage backup. Depending on the extent of the damage, you may end up having your entire septic system replaced, which can cost upwards of $10,000.

How To Build a Raised Garden Bed on a Leach Field

If you have limited space and need to put your raised garden bed on or near your leach field, there are some things you can do to reduce the risk of damaging your septic system. Here are some tips for building a raised garden bed on a leach field:

Choose the Right Location

When choosing a location for your raised garden bed, it’s essential to consider the placement of your leach field. If possible, avoid putting the raised bed directly on top of the leach field. Instead, try to place it to the side or rear of the leach field. This will help reduce the risk of compaction and root intrusion.

If you have no choice but to put the raised bed on top of the leach field, choose a level and well-drained location. This will help reduce the risk of saturation and sewage backup. Check the piping position to avoid accidentally puncturing or breaking them while digging.

Use the Right Materials

Raised garden beds are available in various materials, including wood, stone, and concrete. Wooden garden beds are the most common due to their affordability and ease of construction. However, while they are prone to rot and termites, they are not as heavy as stone or concrete, making them less likely to compact the leach field.

Concrete and stone garden beds are much heavier than wood, so they are more likely to compact the leach field. The excessive weight can also cause the leach pipes to break or collapse.

Build It the Right Way

Once you’ve chosen the right location and material for your raised garden bed, it’s crucial to build it correctly. This will help ensure that it doesn’t damage your leach field or septic system.

When building your raised garden bed, use pressure-treated lumber that has been adequately cured to prevent rot, mold, and insect infestation. The excess moisture in a raised garden predisposes the lumber to these problems, so it’s vital to use pressure-treated lumber that has been properly cured.

Use quality fasteners, such as galvanized nails or screws to attach the lumber. Pre-drill pilot holes to avoid damaging the timber. You can add a plastic lining at the bottom to prevent the roots from penetrating the leach field. While landscape fabric is often used for this purpose, its small holes can allow roots to pass through, so plastic is a better option.

Fill the bed with a high-quality, well-draining soil mix from a reputable garden center. Avoid using topsoil, which can be too heavy and compact the leach field. Choose a lightweight soil mix that drains well to prevent saturation.

Tips for Gardening With a Raised Bed on a Leach Field

Proper care and maintenance of your raised garden bed will help reduce the risk of damage to your leach field while providing you with a bountiful harvest. Here are some tips for gardening with a raised bed on a leach field:

Avoid Overwatering

While regular watering is essential for a healthy garden, overwatering can saturate the soil and compact the leach field. A saturated raised garden exerts more pressure on the leach field, leading to sewage backup.

Water your garden bed deeply and only as needed. Check the soil before watering to see if it’s dry. Insert your finger 2-3 inches (5.08-7.62 cm) into the soil to check the moisture level. If the soil is dry, water deeply and slowly until the soil is moist but not saturated.

It’s best to water in the morning so the plants have time to dry off before nightfall. Avoid watering in the evening, as this can promote fungal growth and encourage pests.

Spread a Layer of Mulch

Mulching your garden bed will help conserve moisture, prevent weeds, and insulate the roots. Use a layer of organic mulch, such as straw, hay, leaves, or wood chips. Apply a 2-3 inch (5.08-7.62 cm) layer of mulch around the plants, taking care not to pile it up against the stems.

As the mulch breaks down, it will add nutrients to the soil and improve its drainage. This will help reduce the risk of saturation and sewage backup. While inorganic mulches, such as plastic or landscape fabric, can also be used, they will not add nutrients to the soil and can exert too much pressure on the leach field.

Fertilize Sparingly

Fertilizing your garden bed will help promote healthy plant growth and bountiful harvests. However, it’s important to fertilize sparingly to avoid overloading the leach field with nutrients.

Use a slow-release fertilizer that will provide a steady supply of nutrients over a period of time. Apply the fertilizer according to the manufacturer’s instructions. Perform a soil test to determine which nutrients are needed and how much fertilizer to use.

Organic fertilizers, such as compost or manure, are also good options. They have high nutrient contents that promote plant growth without overloading the leach field.

Choose the Plants Wisely

Planting on a raised garden bed over a leach field requires proper plant selection. Avoid planting trees or shrubs, as their roots can penetrate and damage the leach field.

Herbs, vegetables, and annual flowers are good choices for a raised garden bed. They have shallow root systems that won’t damage the leach field. Select plants that are well-suited to your climate and soil type.

You can consult with a nursery or extension service to get recommendations for plants that will grow well in your area.

Inspect the Leach Field Regularly

Regular inspection of the leach field is essential for the early detection of problems. Look for sewage backup signs, such as pooled water or strong odors. If you notice any issues, call a professional to have the leach field repaired.

It’s also important to have the leach field inspected by a professional every 3-5 years. They will be able to identify any potential problems and perform any necessary repairs.

Final Thoughts

While a raised garden bed can inhibit evaporation and limit the septic system’s effectiveness, you can still have a beautiful and bountiful garden. With proper planning and plant selection, you can enjoy all the benefits of a raised garden bed without damaging the leach field. Just be sure to practice good maintenance and inspect the leach field regularly to avoid any problems.

Alexander Picot

Alexander Picot is the principal creator of TheGrowingLeaf.com, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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