The right potting mix drains well, has nutrients present within it and is free of weed seeds and disease organisms. Garden soil, even if sterilized, isn't suitable for most container plants as it is too heavy and often becomes compacted over time because it doesn't drain well. A soil-less potting mix is best for container-grown plants because of its superior drainage qualities, according to the University of Illinois Extension Service. Nutrients must be added to these mixes at the time of planting and periodically throughout the plant's life as they have few nutrients of their own.
Sterilize a plastic tub for making your potting mix in. Rinse it in a solution of 1 part bleach to 9 parts water then rinse off with clear water.
Combine 1 bushel of vermiculite or perlite and 1 bushel of sphagnum peat moss. Mix these together well and break up any large clumps of peat moss with your hands.
Add 1-¼ cups of ground limestone to the mixture. Mix in ½ cup of 20 percent phosphate fertilizer and 1 cup of a slow-release granular fertilizer.
Sterilize your planting containers with the bleach solution. Fill them to within 1 inch of the rim with the potting mixture.
Begin additional fertilization for most plants in the third month after planting in the potting mix, as by this time most of the slow-release fertilizer is gone. Use a balanced liquid feed once every two weeks.