Whether to use a liner inside your wooden urban planter boxes isn't a simple yes or no. It depends on your goals for plant health, container longevity, and maintenance. Using a liner, such as heavy-duty plastic or landscape fabric, provides significant benefits. It creates a crucial barrier between moist soil and the wood, dramatically slowing rot and extending your planter's life for years. Liners also help retain soil moisture, reduce watering frequency, and prevent soil from washing out through drainage holes. For growing edible plants, a food-safe liner can prevent chemical leaching from pressure-treated wood into your soil.
However, going without a liner has its merits. It allows for superior air circulation to the plant roots and enables natural "sweating" of the wood, which can prevent waterlogging. The key is excellent drainage. Ensure multiple holes in the planter bottom and consider a base layer of gravel or broken pottery.
For most urban gardeners, we recommend a hybrid approach. Use a permeable landscape fabric liner. It protects the wood from constant soil contact while allowing water and air to pass through. Always ensure your liner has drainage slits or holes aligned with those in the wooden box. This balanced method protects your investment and creates a healthier environment for your plants to thrive in the city.