Concrete and stone planters may not have drainage holes and it is difficult to drill them in without damaging the planter--or the drill. If you have a planter you want to use that doesn't have drainage holes, a gravel lining will provide the needed drainage for the soil without any alterations to the original planter. Another benefit of lining with gravel is that it is simple to replace the flowers in the planter each year or season to change the look of your planters.
Fill the container with a 2- to 4-inch layer of clean gravel. Use 4 inches in large planters and 2 inches in small planters and hanging baskets.
Choose a pot large enough for the plant but smaller than the planter you lined with gravel. Use a pot that has drainage holes in the bottom. A plain plastic pot is fine as it won't be visible once planted correctly.
Fill the smaller pot with a well-draining potting soil. Transplant your plant into this pot, planting it to the same depth it was at in its nursery pot.
Place the smaller pot into the gravel-lined planter so it sits on top of the pebbles. Fill in around the pot with sphagnum moss up to within ½ inch of the rim of the smaller pot.
Water the inner pot as recommended for the type of plant. Excess water will drain into the gravel, where it will be wicked away by the moss. This prevents soggy soil that may damage roots.