Your neighbor gave you excellent advice! Lining a wooden planter box is crucial for extending its lifespan and ensuring healthy plant growth. The primary purposes of a liner are to protect the wood from constant moisture and soil contact, which causes rot, and to help contain the soil while allowing for proper drainage.
Here’s what you can use, from most recommended to other options:
1. Landscape Fabric (Weed Barrier)
This is the top choice for many gardeners. It’s a permeable geotextile that allows water to drain through while holding soil in. It protects the wood from moisture and soil acids but still lets the planter "breathe," reducing the risk of mold. Simply staple or tack it to the interior sides and bottom before adding soil.
2. Plastic (with Drainage Holes)
A heavy-duty plastic sheet or old compost bag can be used, but caution is key. Plastic is excellent at retaining moisture and protecting wood. However, you must punch several drainage holes in the bottom to prevent waterlogging, which kills plant roots. Avoid lining the sides completely with non-permeable plastic, as it can create a stagnant air pocket and accelerate wood rot from trapped condensation.
3. Bubble Wrap or Insulation
In very cold climates, adding a layer of bubble wrap or foam board insulation between the wood and your primary liner can provide extra protection for plant roots against freezing temperatures.
4. Natural Alternatives
For an eco-friendly option, consider a layer of burlap or even newspaper (several sheets thick). These will decompose over time but provide a temporary barrier. They work best for short-term plantings.
Essential Pro-Tips:
* Never make the liner completely waterproof. Drainage is non-negotiable.
* Always ensure there are adequate drainage holes in the planter box itself.
* For the bottom, add a 1-2 inch layer of gravel or pebbles below the liner to further improve drainage.
* The liner should cover the interior sides and bottom but does not need to be sealed shut.
By choosing the right liner—landscape fabric being the most balanced option—you’ll protect your investment, ensure proper plant health, and enjoy your beautiful wooden planter for many more seasons.