Proper drainage is the foundation of a thriving urban garden. Without it, your plants' roots can sit in water, leading to rot and disease. So, what's the best way to layer the bottom of your planter boxes? The goal is to create a system that allows excess water to escape freely while keeping the soil in place.
Start by ensuring your planter box has adequate drainage holes. If there aren't enough, carefully drill several more in the bottom.
The ideal layering system from the bottom up is as follows:
1. The Coarse Layer: Begin with a 1-2 inch layer of a chunky, inorganic material. Excellent choices include horticultural gravel, small lava rocks, or broken pieces of old terracotta pots. This layer creates an empty space at the bottom where excess water can pool away from the soil and roots. Do not use packing peanuts or other materials that can compact; the goal is to maintain air pockets.
2. The Separator Layer: Next, add a permeable barrier. A piece of landscape fabric or a simple coffee filter works perfectly. This critical layer sits on top of the coarse material and prevents your potting soil from washing down into the drainage layer and clogging it over time.
3. The Soil Layer: Finally, fill the rest of your planter box with a high-quality, well-draining potting mix. Avoid using garden soil, which is too dense for containers and will hinder drainage. A mix specifically formulated for containers or raised beds is ideal.
A common myth is that a deep layer of gravel alone improves drainage. This is not true. In fact, adding too much gravel can raise the water table inside the planter, bringing moisture closer to the roots. The key is the combination of a moderate coarse layer and a reliable separator.
By following these simple steps—coarse material, a fabric separator, and quality potting mix—you will create the perfect environment for your urban plants to develop strong, healthy roots and flourish all season long.