Many urban gardeners wonder if applying a sealant to the interior of their wooden planter boxes will extend their lifespan. While this seems like a logical solution, the answer requires careful consideration of your specific gardening needs and the type of wood used.
Applying a waterproof sealant directly to the inside of a planter box can create a barrier against moisture, which is the primary cause of wood rot. This can indeed prolong the life of the wood, especially for planters that will hold moist soil permanently. However, this approach has a significant drawback: it can trap water against the wood if there is any failure in the seal, potentially leading to rot from the inside out.
A more effective and commonly recommended method is to use a protective liner. Inserting a separate, removable liner—such as a heavy-duty plastic sheet, pond liner, or landscape fabric—creates a physical barrier between the moist soil and the wood. This method protects the wood while also allowing for better air circulation and making it easier to replace the liner if needed.
Regardless of your choice, proper drainage is non-negotiable. Ensure your planter has adequate drainage holes at the bottom to prevent water from pooling. For an extra layer of protection, you can apply a sealant specifically designed for outdoor wood to the *exterior* of the planter. This shields it from rain and the elements without the risk of trapping moisture inside.
In conclusion, sealing the inside of a wooden planter can help, but using a dedicated liner is often a superior strategy for combining longevity with plant health. Always use untreated, rot-resistant wood like cedar or redwood for the best starting point.