Liners in planters are commonly used, particularly in raised beds, but are they always necessary? When I first heard about planter lining, this was one of my first thoughts. I weighed the benefits and drawbacks of using liners in my planters at the time.
Using a liner in wooden or metal plant boxes helps prevent them from degrading. Plastic, varnish, and burlap fabric are the best liner materials that could stop such planters from rotting and rusting.
What are the best materials for a liner? Can you use trash bags as low-cost liners for planters? Stay with me because these questions will be answered as we go forward!
Liners are necessary when plant boxes are made of wood, which is a degradable material, and/or metal, which is prone to rust.
Wood is a common material in plant boxes. Since they are prone to degradation when in contact with water, liners should be used to maintain the planter’s integrity.
Considering a plank of wood continuously having contact with water. As time goes by, such planks tend to turn brown, black, and then rot.
This is more likely to happen in the context of gardening since you are watering your plants regularly.
Another contributing factor is the abundance of microorganisms in the soil. If you directly place the soil in a wooden plant box, the microorganism will try to degrade the wood since it is a biodegradable material.
Metal planters are prone to rust, especially in contact with water. Rusting of plant boxes may cause soil toxicity due to the release of chemicals, such as iron, which can cause stunted plant growth and yellow leaves.
Continuous contact of water with the metal interior of a plant box can heighten the risk of rusting. Generally, rusting will not have a direct effect on the plants, but it can cause heavy metal toxicity in the soil.
When too much rust forms, it can get mixed into the soil, and accumulate.
If minerals such as iron are abundant in the soil, it will be hard for your plant’s roots to absorb essential nutrients from the soil such as nitrogen, phosphorus, and potassium.
With difficulties in nutrient absorption, the plant will not have enough resources to use for its optimum growth. This is why stunting and yellowing of leaves happen.
Compare lined planters with garden beds in our article on garden beds.
Using a liner is highly beneficial for gardeners since it 1) hinders biodegradable planters from decomposing, 2) prevents rusting in metal planters, 3) inhibits fluctuating soil temperatures, 4) stops weeds from growing, and 5) hampers the incidence of soil pests.
Using a liner could protect plant boxes that are biodegradable i.e. wooden planters. Liners add a layer of protection as they separate the soil (which is rich in microorganisms) from the wooden surface.
Adding a liner will also hinder the contact of water with metal-based parts of a planter. This will prevent this specific type of planter from rusting and depositing the rust in the soil.
Liners may also act as an insulator for planter boxes. Using a thick layer of plastic sheet for instance will absorb and trap the excess heat from the environment. Thereby, lessening the heat being absorbed in the soil.
If your planters are not raised, using liners will also hinder the weed seeds naturally deposited below the soil surface from growing through your plant boxes.
When you use a liner, you can better control the conditions and protect the soil in your planter boxes. Thus, there is a lesser chance of pests such as ants, gophers, and moles!
Using liners in planters could cause problems like 1) impede proper drainage, 2) get torn apart, 3) make changing soil tedious, and 4) add up on gardening expenses.
When liners are used, drainage is also affected since you confine the soil. However, this is avoidable through simple means!
Gardeners can poke holes in planter liners to ensure ample drainage. This is done to avoid the accumulation of water below the soil that can cause diseases from fungi and bacteria.
Liners can also be damaged especially during maintenance activities such as digging using a trowel.
Incurring a big tear on the liner, especially if it is made from easy-to-tear materials like plastic and sacks, will defeat its purpose of protecting wooden and metal planters.
It will also take an effort to remove all the soil from your plant boxes and put them back after being able to change the liner.
You will spend more money since liners are an additional garden input. High-quality liners packed individually may cost more than 20 USD each. However, I am providing you with cheaper options across the article, so buckle up and take notes!
The best materials for a liner are plastic, varnish, and burlap fabric. This is due to their protective nature, waterproof properties, and drainage capacities.
Plastic is the best lining material for planters made of wood. This is because it is thick and non-biodegradable, so it can protect the wood planter from degradation due to water and soil microorganisms.
Using plastic can be effective in lining both wooden and metal planters.
A plastic planter liner could be in the form of:
- Polyethylene sheets
- Trash bags
- Thick plastic covers
- Plastic pots
- Plastic tarps
You can be creative and resourceful in using plastic as your planter’s liner. Some gardeners I know reuse old plastic sheets, tarpaulins, and even plastic covers.
The only criterion you need to look for in a liner is its durability. When reusing, do not use those plastic sheets that are close to tearing apart.
However, if you have an allocated budget for a liner, you might consider the product below which is available on Amazon.
As I have explained previously, using a liner can protect your wood planters. In fact, using liners can turn them into waterproof containers for your plant babies!
Lining the interior of wooden plant boxes with a thick coat of varnish is a simple way of waterproofing garden planters.
This approach is only applicable to wooden plant boxes.
Using varnish to waterproof a wooden plant is cost-effective because of 3 factors:
- Easy to do. What can be easier than just brushing the inside of a wooden plant box? Compared to the plastic sheets—where you will measure, cut, assemble, and attach—this approach is easier.
- Effective. This factor can be attributed to varnish’s hydrophobic chemical properties. I have varnished a lot of wooden platforms myself, and I can tell that using varnish really makes wood waterproof!
- Cheap. A bottle of varnish may cost less than a couple of dollars! You can check the product below on Amazon.
The critical aspect that you need to take note of here is that the varnish layer must be at least 2 coats so that it will be thick enough to protect the wooden planters.
Burlap fabric is an effective lining material because it allows for sufficient drainage while also acting as a barrier against soil particles that can degrade wood and metal planters.
One important aspect that liners hinder is drainage, as you can recall from the cons section. This is the reason why plastic liners must be perforated before being used.
However, in the case of netted burlap fabric, this extra step is no longer necessary. Burlap liners already have small holes where water can pass through for optimal drainage.
Learn more about drainage in our article on drainage in planter boxes.
I think you are also wondering—so water can still pass through, why should we use this?
Burlap fabric is still being used because it is a cheap option. Aside from that, only a small amount of water passes through it in a slow-release manner.
Check out this burlap liner on Amazon if you want to try it out!
But even with these advantages of burlap fabric, it is still best to use it with other liner options. Use a burlap fabric liner along with a varnish coating if you have a wooden planter. Otherwise, use it with a thin layer of the reused plastic sheet if your planter is made out of metal.
Do liners make the soil waterlogged?
Liners can make the soil waterlogged if there are no drainage holes in them. This is the reason why plastic liners need to be perforated to facilitate the drainage of water, and not cause further problems such as water logging and worse, root rot diseases.
Do liners rot?
Liners made from biodegradable materials such as plywood and cedar will surely degrade with time. If used continuously over the years, they will rot. Thus, the most common liners used by gardeners worldwide are non-biodegradable such as plastic.
Is it better to use a waterproof planter?
If one has a budget for a waterproof planter, it is the best option as buying liners for planters that aren’t water-tight will even cost more in the long run. Waterproof and raised plant boxes like this one from Amazon would be a good choice, for gardeners looking to invest in high-quality planters.
Is it advisable to use organic materials for a liner?
It is not recommended to use highly organic materials as liners, such as coco coir, peat moss, or leaves, because they can speed up the degradation of wood and metal planters. They are more likely to decompose and be absorbed by the soil as well, which can improve soil quality but not protect the planter.
Liners in planters must be used to protect the integrity of the plant boxes made of wood and metal which are prone to decomposing and rusting, respectively—especially with regular watering
Plastic materials including polyethylene sheets, trash bags, thick plastic covers, plastic pots, and plastic tarps are the best materials to use as liners. Applying a thick coat of varnish or laying down a burlap fabric liner can also help protect wooden and metal planters.