When putting plants into a container garden you should never use garden soil. Garden soil contains microbes that can seriously harm plants when confined to a container. Potting soil is a soilless mixture that you can use in place of garden soil in containers. Typical mixtures of potting soil include loam, peat moss and a drainage mix such as perlite, vermiculite or sand. They may also contain some type of granulated fertilizer or manure. You can make your own potting soil or purchase potting soil in bags from your local garden center.
Create your own potting soil by mixing 1 part peat moss, 1 part compost and 1 part vermiculite.
Place the soil in an oven bag and put the oven bag into a roasting pan. Place the probe of an oven thermometer through the mouth of the bag and into the center of the soil.
Set your oven temperature to 250 degrees.
Place the soil mixture into the oven and bake it until the oven thermometer shows that the center of the soil reaches 180 degrees.
Turn off the oven and allow the soil to cool before removing it.
Mix a granular fertilizer into the soil in a concentration recommended by the fertilizer packaging. The amount of granulated fertilizer used varies among brands.
Determine what size container you need based on the eventual size of the plants. Plants with a large root ball should go into a container that is only 1 to 2 inches in diameter larger than the root ball. You can place between one and four smaller plants in an 8-inch container, between four and seven plants in a 10-inch container and between five and eight plants in a 12-inch container.
Fill a container one-third of the way full of potting soil for plants with a large root ball. Place items with a large root ball into the soil. Fill in around the sides of the root ball with more potting soil until the container is filled. For smaller transplants such as annual plants, fill the container completely with potting soil. Open a planting pocket for the container with one hand and place the root ball of the transplant into the planting hole. Close up the soil around the plant.
Check the container daily by placing your finger into the soil up to the second knuckle. Water when the soil feels dry to the touch. The soil saturation varies among plants. In general, you should water your plants so that the soil feels damp to the touch.