Container planting brings color to patios, balconies and decks. It expands the areas available for planting, like the front entryway, or provides a focal point in the garden. Garden soil is too heavy for containers, compacts easily, dries out quickly and carries fungus and insects. Match the potting soil to the plant for optimal growth.
Orchid potting soil is not really soil at all but a bark mixture. Orchids prefer a humid environment but don't like their roots wet. The bark retains enough moisture to feed the roots but all excess water drains out. You may have noticed that when you buy an orchid it comes in a pot that has slits in the side. The pot also seems small for the height of the orchid as well. Orchids actually grow on wood with their roots exposed to the air in the wild. Orchid potting mix provides a support for the plant so it can grow in a pot. Besides commercial orchid potting "soil," orchids will grow in sphagnum moss, bark, coconut fiber and charcoal.
Potting soil for cacti is similar to that of orchids in that the soil does not retain moisture. It does have some nutrients from organic materials. Make your own cactus potting soil by mixing equal parts sand, fine gravel and regular potting soil. When planting cactus or repotting, tamp the soil around the base of the cactus but don't water. Bruised cacti may rot when exposed to water. Wait a week, then water.
Plants in pots outside dry out more quickly than plants in the ground. Even if the pot is glazed or plastic, the plant still will dry out faster. Moisture-retaining potting soil has water-retaining polymers, or crystals, that soak up the water and then release it as the surrounding soil dries out. Another way to help potted plants stay moister longer is to line the bottom third of the pot with several layers of newspapers or paper towels. Layer the paper over the bottom of the pot as well.
Several manufacturers of potting soil include slow-release fertilizer pellets in the potting mixture. It's convenient and you know that the right amount has been mixed in proportion with the soil.
No frills and the least expensive of potting soils contain a mixture of perlite or vermiculite, peat moss, and bark. Organic material other than the bark may have been added as well.
Other than orchid potting soil, there seems to be a potting soil for nearly every type of plant with special needs, from African violets to azaleas and gardenias. Know the requirements of your plants and amend regular potting soil with the additions required by the plant. For example: Gardenias like acid soil so water with a mixture of weak tea and a squeeze of lemon.