Getting your planters ready for the season ahead? Lining them is a simple step that makes a real difference.
A good liner keeps soil moist, protects roots from temperature fluctuations, and stops compost washing out through drainage holes. For wooden planters in particular, it is the most effective thing you can do to prevent rot, since it is the constant contact between damp soil and wood that causes most of the damage over time. Metal planters benefit too, as a liner slows the onset of rust and corrosion.
This guide walks you through choosing the right liner, fitting it correctly, and getting the drainage balance right so your planter performs well year after year.
What to Use as a Planter Liner
The best liner for your planter depends on what it’s made of and what you plan to grow. Here are some popular options:
- Plastic sheeting or black bin liners: Inexpensive and easy to find. Good for moisture retention, particularly in terracotta or metal planters that dry out quickly. Pierce for drainage before use and avoid wrapping too tightly.
- Landscape fabric: Allows water to drain through naturally while keeping soil in place. A practical middle ground if you want something more breathable than plastic and more durable than coir.
- Coir liners: Made from coconut husk, these allow air and water to circulate and have a natural appearance. Coir liners break down faster than synthetic options and will need replacing every few seasons.
- Damp proof membrane (DPM): Tough, waterproof, and easy to cut to size, DPM is widely recommended for wooden planters. It is not always stocked in garden centres but is readily available from DIY and builders merchants.
Other materials such as pond liner, old compost bags, or hessian can also do the job if that's what you have to hand.
Lining a Planter Box: Step-by-Step Instructions
Follow these six easy steps to create a successful planter:
1. Measure the planter
Measure the interior dimensions of your planter, including the length, width, and depth. Add a little extra to each measurement to allow for overlap and securing the liner properly.
2. Cut the liner
Cut the liner material to the right size using scissors or a knife based on your measurements. Ensure the liner is big enough to cover the inside of the planter completely, with extra to fold over the edges.
3. Fit and secure the liner
Press the liner into the planter, pushing it into the corners and smoothing it against the sides. Fold the excess liner over the edges of the planter and secure with staples or nails for wooden planters. Adhesive tape or glue can be used to secure the liner in metal, terracotta or plastic containers.
4. Make drainage holes
If you're using a waterproof liner such as plastic sheeting or a bin liner, use scissors or a knife to pierce a few small holes in the base for drainage. If you're using landscape fabric or coir, water will drain through naturally.
5. Add gravel and compost
Lay a thin layer of gravel or chippings across the base before adding your compost. This helps stop soil washing out through the drainage holes and keeps water moving freely through the planter. Once your compost is in, you're all set to start planting.
Common mistakes to avoid
- Using a non-breathable liner for plants that need good airflow.
- Cutting the liner too small, leaving gaps at the sides or base.
- Not securing the liner properly so it slips or folds during planting.
- Leaving excess liner above the rim, which can wick water onto the planter edges.
- Not piercing drainage holes in waterproof liners before planting.
The importance of drainage
Proper drainage helps to prevent waterlogging, which can lead to root rot and other plant diseases. While liners help retain moisture, it is important to balance this with adequate drainage.
Always check that your planter has drainage holes in the base. If not, drill a few small holes to let excess water escape. Don't make the holes too big or it might not hold the soil well. When using a waterproof liner like plastic or pond liner, pierce small holes in the liner directly above the planter’s drainage holes. Permeable liners such as landscape fabric or coir usually do not need extra holes.
Maintaining your planter
Once you’ve lined your planter and filled it with an array of beautiful plants it’s important to keep it well maintained. Check for signs of waterlogging regularly and make sure drainage is working properly. Continue to check water levels and adjust as appropriate through the seasons. In winter, consider insulating your planter using plant fleece to protect roots from frost.
Check the liner every time you replant, looking for tears, thinning, or signs of decay. Coir and other natural liners break down over time and will need replacing every year or two. Plastic and fabric liners last longer but can split or perish, particularly through winter.
If you're looking for planters, liners, or compost to get started, you'll find a good range in store and online at Bents.
FAQs
Do all planters need lining?
Not all planters need a liner, but most will benefit from one. Wooden planters should always be lined, as contact between damp soil and timber is the main cause of rot. A liner helps metal planters too, slowing corrosion. Terracotta and plastic planters don't need lining for structural reasons, but one can help retain moisture if your plants need it.
Can I use a plastic bag or old compost bag as a planter liner?
Yes, a plastic bag or old compost bag can be used as a planter liner. Both work well as a low-cost option. Pierce a few small holes in the base for drainage, and if you're using a compost bag, place the black side facing the soil. They won't last as long as a purpose-made liner but are a practical choice for most situations.
What's the best liner for a wooden planter?
The best liner for a wooden planter is one that keeps moisture away from the timber to prevent rot. Damp proof membrane (DPM) is widely recommended for this reason, though heavy-duty plastic sheeting works well too. Make sure it fits snugly and has drainage holes to stop water pooling at the base.
How often should you replace a planter liner?
How often you need to replace a planter liner depends on the material. Coir liners typically need replacing every year or two as they break down over time. Plastic, DPM, and landscape fabric liners can last several seasons but are worth checking each year for tears or wear before replanting.