A seashell dish garden allows you to combine a beach theme with the relatively easy care of a succulent. Succulents come in all shapes, sizes and colors. Most varieties grow slowly, making them especially well suited to a small seashell container. Stonecrops (Sedum spp.) and hen-and-chicks (Sempervivum spp.), which generally grow in U.S. Department of Agriculture plant hardiness zones 3 through 8, work well for both indoor and outdoor shell gardens in most climates.
Any seashell with an opening large enough for at least one succulent and deep enough to hold the soil mixture will work for a shell garden. Consider using a coiled shell, like a conch, or flat, more dish-shaped shell, such as a large clam or cockle shell. Clean the shell in warm water, removing any dirt or soil from both the exterior and interior surfaces with a soft-bristled brush. Disinfecting the shell in a solution of 1 part bleach and 9 parts water before you plant prevents disease and fungus problems later.
Filling the Shell
A 1/2 to 1 1/2 inch layer of clean gravel provides drainage inside the shell. Covering the gravel with a thin layer of activated charcoal prevents any odors from forming in the standing water that may collect in this gravel layer. Succulents need a fast-draining soil. You can use a cactus potting soil mix or create your own by combining equal parts potting soil, coarse sand and peat. Fill the shell to within 1/4 inch of the shell's rim with the soil and water it lightly until it's evenly moist but not soggy.
The smaller succulents are difficult to handle without damaging the leaves, so use a small spoon to transplant them into the shell. Make a divot in the soil with the tip of the spoon or your finger, then scoop the succulent from its old pot with the spoon and set it into place so they are at the same depth they were growing at previously. If you do handle the succulents, lift them by the tips of the their leaves and handle them gently to avoid damage. The succulents only require about 1 inch of space between each other.
Succulent shell gardens rarely if ever need fertilizer. Using fertilizer makes the plants grow quickly and they will outgrow their shells. Most succulents grow best in bright but indirect sunlight, and they can survive temperatures between 40 and 90 degrees Fahrenheit with no damage. Your dish garden only requires watering when the soil mix has almost completely dried out. Provide just enough water to moisten it. Succulents rarely suffer from pests or diseases, although root and stem rot can occur if the soil is kept too moist.