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Do I Need A Liner In My Raised Bed? If you are planning your new Vegetable or Ornamental Garden in your yard at home there are many factors that need to be considered in the construction phase of the garden. The size, height, and layout of the beds and what they are made out of. But do I need to protect the edges of the garden bed with a liner?
It is generally a good idea to use a liner to protect the edges of a garden bed, raised or not, from coming into direct contact with the soil. This will extend the life of the material significantly, particularly in cases where timber is used. The life span of low-quality timber unprotected pine is little as 5 years depending upon the conditions.
Additionally, in cases where chemically treated timbers, such as treated pine are used liners are highly recommended. Many timbers are treated with CCA (Copper Chrome Arsenate) which has been shown to prolong the life of the wood but the chemicals do leach into the soil over time with the highest concentrations being detected at the surface of the soil according to a University of Florida study.
What Are The Pros And Cons of Garden Liners?
While garden liners are generally recommended in most cases there are both advantages and disadvantages to using them.
- The liner protects the structure from contact with soil and moisture.
- A liner at the base of the bed prevents burrowing pests such as rabbits, gophers and from entering the bed from below
- It can prevent invasive weeds from getting underneath the sides of the bed.
- They prevent chemicals from timbers leaching into the soil if a nonporous variety is used
- Some Liners are easily damaged and are difficult to replace due to the need to dig out all the soil.
- The use of a liner will reduce the degree of drainage in some cases.
- Once water gets between the liner and the wall of the raised bed it is difficult for it to escape. The can actually accelerate the deterioration of the structure.
Best Materials To Use As Garden Liners
There are several different options that can be select to be used to line your garden. There are listed below;
- Weed matting is a woven material made from polypropylene. It will allow water to pass through it, is long-lasting, and relatively cheap. Click here to see the latest price on Amazon
- 4 MIL Black Plastic is a continuous plastic sheet also made from polypropylene that will not allow water to pass through it. It will completely protect the sides of the raised bed but drainage of the water will need to be considered. To see the latest price click here to visit Amazon.
- Pond Liner can also be used for this job. It is similar to the 4 MIL Black Plastic except that it is about twice as thick. The increased thickness will make the liner more durable, more difficult to damage, and more expensive. Click here to see the latest price on Amazon.
- Geotextile is by far the most durable and highest quality option for a liner. It is around 5 times thicker than other options and is UV stabilized to extend the life of the fabric while remaining water permeable. If you want to protect your structures for the long term this is the product I would select, click here to see it on Amazon.
How To Extend The Life Of A Raised Garden Bed?
Apart from lining the raised bed, there are a number of other measures you can take to extend the life of your bed, the most obvious being to select durable materials to build the bed from.
What Are The Best Materials To Build A Raised Bed From?
For me the simplest, quickest, and most durable option, apart from stone or brick which is the most expensive, to build raised beds from is galvanized steel. Prefabricated beds can be selected purchased in a range of sizes that are quick and easy to assemble, most beds will take less than 10 to 15 minutes to assemble.
The galvanized steel beds will typically last 20 to 25 years possibly longer due to the nature of the material and the fact that many prefabricated beds have internal and external coatings which also help prolong the life of the structure.
An example of the product we recommended is shown in the picture below, the advantage of this product is its height and color. The height is sufficient to allow it to be placed directly on concrete if required while its color will maximize its capacity to absorb solar radiation and therefore heat up the soil, to see the latest price click here to visit Amazon.
The other common option to build raised beds from is timber. While prefabricated options are available we generally don’t recommend buying them because it is difficult to tell what quality of wood has been used in the construction.
If you are considering constructing your own raised garden beds we generally recommend selecting higher quality timbers. According to the Versace Timbers, wood is classified into 4 classes.
- Class 1 Timber is considered to have the highest level of natural durability and is expected to last around 25 years when it direct contact with soil. Timbers include Blackbutt, Ironbark, Spotted Gum, and Forest Red Gum.
- Class 2 Timber consists of hardwood species that have an average life expectancy in-ground of 15 to 25 years. Common timbers within this group include Blue Gum and Jarrah.
- Class 3 Timber is the lowest quality hard would and includes varieties often used in decking applications. These species will typically last 5 to 15 years in the ground. Common varieties include years Stringybank, Kwila/Merbau, Western Red Cedar, and Tasmanian Oak.
- Class 4 Timber are the lowest quality timbers and will last 5 years. Most varieties of pine are included in this group.
To improve durability, class 4 timber, in particular, is often treated to improve durability. There are 6 levels of pressure treatments (H1, H2……etc.) used with the higher number being the more durable. Most hardware stores offer H3 or H4 pine, which can be used for in-ground applications for a few years.
The most durable option is to use bricks or cement. One of the quickest and easiest way to build the raised garden beds is to use Besser bricks/blocks which are relatively large and generally require less skill to lay.
Another initiative way to create a raised garden bed using perform molded concrete. They are laborious to make, as you will see on the video below however the end result is both attractive and durable.
Other Raised Bed Design Factors That Can be Used To Extend The Life Of A Raised Bed?
The life of a garden bed can also be extended by protecting the bottom of the structure by ensuring that the bottom edge of the structure is not in direct contact with the soil. This can be achieved by creating a foundation below that structure that elevates above the ground slightly above the ground.
The elevation of the structure will reduce the amount of time that that the raised bed is exposed to moisture. This is particularly important in cases where the area that the bed is situated is known to have poor drainage. Foundations should typically be made out of cement, stone, or bricks as this is highly durable.
In addition to foundations, a layer of coarse rocks at the base of the raised bed can also be used in improving drainage and therefore reduce the structure’s exposure to moisture.
However, if this strategy is used there are a few important considerations that need to be taken into account. The first is that for the layer to remain to be effective for the long haul it is important to ensure that the rock layer remains separated from the soil within the bed. To achieve this separation it is best to place a layer of geotextile over the rocks.
The second consideration is how the addition of a layer of rocks will affect the depth of the soil in the raised bed. This will be dependent upon the type of plants that are grown, however as a general rule at least 1 ft (30cm) in depth would be recommended.