Things You'll Need
Granite or gravel
Planter boxes adorn the outsides of countless homes, offices and other buildings, breaking up the architectural landscape with bright flowers and fresh plants. These boxes can serve as gardens in areas where space allowance or climate prevent large-scale gardening efforts. The most important aspect of preparing to garden in a planter box is to provide proper drainage and nutritional support for the plants, which is done by layering soil and amendments for the healthiest plants.
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Fill the bottom of your planter box with 6 to 8 inches of crushed granite or gravel. This layer of small rocks will allow for water to drain effectively from the planter, preventing damage to the roots from sitting water.
Cover the granite or gravel with a layer of landscape fabric. This fabric features small holes for water drainage, but will stop the soil from washing away with the water.
Fill the rest of the planter with well-draining potting soil. You can purchase soil at a garden center or nursery, or create your own with a mixture of soil and a drainage aid like peat moss.
Add a 1-inch layer of plant-specific fertilizer once you add plants to your box. Because the soil in the box is isolated, you will need to add soil or liquid fertilizer every few months to provide enough nutrients for the plants.
If you have a planter box with large holes in the bottom for drainage, cover the bottom with landscape fabric before adding the granite or gravel. This will stop the rocks from falling through the holes.
When choosing soil, consult the specific needs of your flowers. Some may require soil high in certain nutrients, such as nitrogen or phosphorous.