Choose a container with large drainage holes at the bottom. If the clay, plastic or ceramic pot you love does not have holes, pierce holes in the bottom of a smaller plastic container, place it inside the pot and prop it up on gravel to drain.
Fill a container three-quarters full with potting soil. Water the soil lightly so that it is damp; do not over-water so that the water forms a puddle in the soil.
Place your seedling directly in the pot if it is growing in a peat pot. The peat pot will break down and add organic material to your soil.
Remove the seedling carefully if it is growing in plastic container. Turn the container sideways and gently tug on the base of the seedling, being careful not to disturb the roots. Tug on the base, then the container, until you dislodge the seedling from the container.
Place the seedling in the pot so that the top of the root ball is level with the soil surface. Press the seedling firmly into the soil. Add more potting soil and pat the soil around the base of the seedling.
Place other seedlings in the pot at least 4 inches apart to give the seedlings room to grow and spread out.
Add a thin layer of mulch so that it is evenly dispersed along the top of the soil. Mulch will help keep the soil moist, which is important because moisture evaporates more quickly from a container than it does from the ground.
Water the geranium thoroughly.
Mix a solution of water-soluble fertilizer a week after transplanting your geranium seedlings. Fertilize your geranium every week or two (following the package’s instructions) throughout the growing season.