Before you fill your urban planter box with soil, creating a proper foundation is crucial for plant health and vitality. The bottom layer serves two primary purposes: drainage and aeration. Excellent drainage prevents water from pooling at the roots, which can cause rot and other diseases. Good aeration ensures that the roots receive the oxygen they need to thrive.
So, what should you use? The best material is a simple drainage layer. Start by covering the drainage holes with a permeable barrier. Landscape fabric or a piece of fine mesh screen are excellent choices. This prevents soil from washing out while still allowing water to escape freely.
Next, add a layer of coarse, chunky material. Aim for a depth of 2 to 4 inches, depending on the height of your planter. Ideal materials include horticultural gravel, small lava rocks, perlite, or even broken pieces of old clay pots. Avoid using non-porous materials like solid plastic or packing peanuts, as they can impede drainage and create anoxic conditions.
This layered system creates a reservoir for excess water to drain away from the soil and root zone. It mimics the natural, well-draining conditions that most plants love, leading to a more successful and flourishing urban garden.