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Garden Bed Against a Brick Wall: What You Should Know

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Building an elevated bed against a brick wall is useful for planting flowers, fruits, vegetables, and other different types of plants. It can save huge space in your garden and normally built-in corners.

Garden soil can cause a brick wall to become weak due to moisture and root ingression into the foundation. Building a garden bed against a brick wall can be done safely by using a barrier placed between the soil and the wall. An added layer of protection can be used by building the garden bed 12 to 24 inches away from the wall. 

Building a raised bed against a brick wall is a common practice and it can be done by anyone, however, there are a few things to consider before you start laying down your grand plan.
These are –

  • Protection against moisture 
  • Protection against roots
  • Protection against pests

I know that there are many good moisture barriers out there, but I have found this polyurethane waterproof barrier on Amazon, which is cost-effective, durable, and of excellent value for money.

polyurethane sheeting to protect from moisture

How to Waterproof a Wall’s Foundation

Wall protection from garden beds and plants

The foundation of the walls must be protected from underground and outside water seepage. 

To make sure that water does not enter the wall’s foundations, you should use a waterproofing system.

There are several methods you can use to prevent moisture ingress into a wall’s foundation. 

Here we have listed the more popular methods –

Heavy polyurethane coating

This is a synthetic coating and is usually two to three times thicker than normal coatings. 

The purpose of the coating is to prevent moisture ingression from the outer walls into the inner parts where it can cause stresses and cracks over time.

The coating should be applied on a properly dried surface cleaned of any debris or dirt which can cause it to flake off afterward.

Concrete Penetrant

Penetrating sealers work by increasing surface tension on the concrete. 

These products will create hydrophobic water-shedding, meaning water will quickly be repelled from the sealed concrete surface instead of soaking in.

It reduces a substrate’s ability to absorb water or stains at the molecular level.

This coating should also be applied to a clean and dry surface.

Fiber Cement Board

Fiber cement board is one of the better choices of building materials that work on home exteriors to prevent moisture from seeping into the house’s foundation. 

The pores in the concrete fiber are too small for water molecules to ingress and cause a problem.

The edges must be sealed to prevent moisture from passing as well because if it is not sealed it will nullify the effects of having the barrier there in the first place

Epoxy for Walls

Epoxy acts as a protective and decorative paint to prevent moisture ingress on cement-based substrates, such as concrete, plaster, cement-mortar, and cement boards. 

The surface to be treated must be dry and stable, as well as being free from any materials that would hinder bonding, such as dust, loose particles, grease, etc.

Pool Liner

Using a pool liner before the addition of soil and other substrates on a garden bed can help prevent water from going in the wrong direction.

The plastic pool liner should be placed on the wall surface closest to the house where the garden is to be located. The garden is then constructed on this liner moving outwards from the walls of the house. 

Bitumen Paint

Bitumen paint acts in a similar manner to epoxy, which coats and protects the wall’s surface against the negative effects the bare dirt can have on a wall.

It is very cheap, readily available, and can be easily applied using a paintbrush. 

Tree Root Barrier

A tree root barrier will not directly protect the wall from soil. 

What it actually does is prevent roots from trees and plants from venturing close to your home by posing a hard barrier to prevent growth in unwanted directions.

Roots can cause cracks in concrete structures and house foundations by absorbing moisture causing the soil to subside beneath the foundation. A void is created which removes the support from under the foundation causing stress and unwanted cracks.

Additionally, the roots themselves can place additional pressure on the foundation and walls as they grow bigger, which also causes stress and cracks.

To find out more about roots and their effects on concrete foundation you can see our detailed article here.

Benefits of using a barrier lining during construction

Garden against a wall

A barrier lining is very useful in the construction of raised bed gardens and will help protect walls and other foundations from the effects of having plants closeby. 

  1. A lining can protect close-by walls from wandering roots.
  2. It can also maintain run-off water in the soil. 
  3. Keeps the soil protected from weeds and pests such as termites.

Keeping Roots at Bay

Roots can cause cracks to concrete structure and house foundations by absorbing moisture causing the soil to subside beneath the foundation.

A void is created which removes the support from under the foundation causing stress and unwanted cracks.

Promoting Water Runoff 

Raised bed gardens are constructed so that it utilizes amended soil for the efficient growth of plants and vegetables. 

This soil would therefore have properties that would 

  • provide good nutrients to the plants
  • aeration for plant roots
  • Good drainage 

Protection from weeds and pests

A lining barrier would prevent weeds from the existing soil from infiltrating into the nutrient-rich soil that is intended for your plants.

If they are allowed to do so they can rob your plants of nutrients by competing for space within the raised bed.

Additionally, pests like termites are naturally found in untreated soil and can also easily infiltrate into the amended soil mixture. 

Termites in your raised bed can cause problems if you are using wood as the siding material and they can easily eat through hence weakening the raised bed structure. As a result, the wood would break with very little pressure. Learn more about how termites can affect your garden.

Will the Soil Affect the Wall?

Yes! The soil will affect the wall because as the soil sits against the brick and mortar structure, the moisture from the soil will slowly start penetrating into the brick wall. 

Over the course of time, the wall structure will weaken from the routine watering of the plants in the raised bed.

It can also provide passage to underground soil termites and insects to enter the house, so it will never be a good idea to simply place soil against any wall structure without the proper protection in place.

Should you Join the Garden Bed to the Wall?

Garden beds can be joined to the wall. However, over time, if bricks are used it can come loose from the wall because it was not part of the initial structure when the wall was being built. 

To prevent any soil from washing away when this happens you can line the raised garden bed with a protective liner as previously explained.

Many homeowners are faced with this same problem after they have purchased preowned homes.

The parts where the bed joins the wall just separate.

What you can do to fix the issue which may seem a crack is to fill it. A simple mortar filler mix will do the trick.

Are Bricks from the Wall safe for Raised Beds?

The bricks from the wall will not affect the raised bed garden. However, there is one concern with having soil next to bricks. Fly Ash!

Fly ash is a masonry additive that contains heavy metals such as radium and arsenic and is often used in concrete products for added durability. However, there isn’t much scientific evidence stating that fly ash does leak into the soil. 

The barrier used for moisture ingress will also prevent chemicals from leaching from concrete into the soil. 

Can Roots Cause Damage to the Wall?

Plant roots can damage the wall by:

  • Causing stress and cracks in the wall
  • Absorb underground water and spread moisture to the wall bricks

When roots absorb water, the moisture level is lowered, resulting in shrinkage of the soil. This shrinkage causes the movement of underground soil, and the foundation is disturbed.

The same happens when water is lost during transpiration, and pressure is developed on the walls by the roots that will cause cracks to concrete.

For this reason, it is also recommended that raised bed gardens be constructed 1 to 2 feet away from a wall so that the wall would not be affected by the roots from the garden.

Stop Roots in an existing garden

If you want to prevent root problems in your existing raised bed, you will have to install obstacles to stop spreading plant roots in raised beds. 

Or you can simply dig a 1-ft deep channel around the outer limits of the raised bed and compress the soil at the bottom to compact it and make it more difficult for the occupying roots to grow.

To stop roots from becoming a problem in the garden you can use Herbicides applied directly to the soil surface that are carried down into the root system with rainfall or watering. 

The chemicals kill the roots when they come into direct contact with them.

Chemicals that work in this way include bromacil, hexazinone and tebuthiuron.

How to Build a Garden Bed Against a Wall

Following steps must be followed to build a raised garden against your house wall:

  1. Dig down into the soil

    Deeply dig the ground (almost 10-20 inches deep) for the construction of a bed.

    Compact the surface soil with the help of a heavy log and level the surface using a level meter for good drainage. 
  1. Cast bricks around the excavated area

    Construct a framework of the raised bed with bricks so finished front and back part of an excavated area with cement blocks or bricks.
  1. Line another layer of bricks

    You can join the bricks to the wall or line another layer in front of the existing wall.
  1.  Install waterproof barrier

    Now install a waterproof thick plastic sheet or cotton fabric to make the barrier between the wall and bed.
  1. Add first layer of organic material

    Line the bottom of a garden with organic material which would add nutrients to the soil as it is being broken down. This is also done to help fill the garden bed without having to add a lot of nutrient rich soil which will increase the cost of the project.
  2. Add soil

    Add a layer of soil mixed with nutrients and organic fertilizer on top of the organic material.
  1. Add plants

    Now the bed is ready for different plants such as flowers, fruits, veggies, or mixed ones.

Walls you can Build a Raised bed Garden Against

You can build walls of raised bed garden along following material such as:

A Fence

You can make the boundary of raised beds by wooden fences, bamboos, plastic bottles fences, empty cans and tins, glass bottles, cement bricks, concrete blocks

House walls

Raised bed gardens can be built against house walls but there must be some precautions you must follow. Keep 2-4 inches distance to build a bed against house walls because it can cause dampness and holes in the house wall.

Front walls

You can use front walls to enhance the beauty of the entrance through raised beds. Same precautions must be followed to keep 4-6 inches away from the wall.

The Downside of having a raised bed against brick walls

When you want to design your garden rooftop or courtyard through raised beds beware their demerits before construction:

Lack of sunlight 

One thing to consider when building a raised bed against a wall is sunlight. If the wall is south facing then you would not have much problem.

In the northern hemisphere, the sun will provide almost 12 hours of full sunlight during the daylight hours which is beneficial to the plants that are on the southern side of a wall structure.

However, if the wall is eastern or western facing then the amount of sunlight that the plants will receive will be limited. This will affect the overall production of crops during the growing season (beginning of spring to the end of fall)

Waterlogging and Salinity Problems

Over the course of time, if a barrier isn’t used to protect the wall’s structure from moisture, the wall will begin to absorb water and weaken. 

This in turn will lead to cracks if any pressure is placed on the wall by the natural movement of soil.

Take the guesswork out of watering plants and keeping the soil moist. It is both cost-effective and durable.
Best of all, it also measures pH and light. It’s worth a look.

Trazon Soil pH Meter 3-in-1 Soil Tester Moisture

Promotes Pests and Insects

Having soil against a wall, in this case, the walls of a house can bring unwanted pests into your home. 

Termites are subterranean insects that thrive in moist and dark conditions. Termites get nutrients from cellulose, an organic fiber found in wood and plant matter.

This means that they can eat into any wooden structure in your home and can easily make any home unlivable by weakening its structure.

Can I build raised bed along the house foundation

No, it is not such a good idea to plant anything along the house foundation whether it is raised bed or a simple garden. It can weaken the house foundation through water seepage and the spreading of plant roots.

What Should You Put in the Base of the Raised Beds?

You should make the base of the raised bed with a wooden sheet to avoid weeds and cover this base with dead leaves, rotten plants, grass cutting, wood chips, straw, and carbon-based material.

For an added layer protection, you can use ground cover or shade cloth to promote drainage and prevent loss of soil.

The Takeaway

Raised bed gardens are eco-friendly and sustainable.

They enhance the scenic beauty of the home while at the same time, utilizing very little space.

In order to have a garden bed against a wall, you have to put in place the necessary protection so the soil would not affect the strength of your wall structure or even your homes.

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