Wondering how to fill those deep, beautiful urban planter boxes without breaking the bank or using mountains of soil? You're not alone. The most economical approach uses a method called "planter box filler" or creating a false bottom. Instead of filling the entire box with expensive potting mix, you use lightweight, bulky, and often free or low-cost materials to take up space at the bottom.
Start by placing a layer of drainage material like broken terracotta pots or pebbles at the very base. Then, add your bulk filler. Excellent options include upside-down plastic pots, crushed and rinsed plastic bottles, natural materials like untreated wood logs or cork, or even packing peanuts (biodegradable starch-based only). Cover this layer with a permeable barrier, such as landscape fabric or a layer of straw, to prevent soil from washing down. Finally, fill the top one-third to one-half with high-quality potting soil. This is where your plants' roots will grow.
This method offers multiple benefits: it saves up to 50-70% on soil costs, makes large planters much lighter and easier to move, improves drainage to prevent root rot, and is an excellent way to repurpose recyclable waste. Your plants will thrive with their roots in the nutrient-rich top layer, and your wallet—and back—will thank you.