Most plant experts recommend a soilless mix for houseplants and outdoor plants in containers. Garden soil isn’t considered suitable for potting applications because its quality is so variable—it may be heavy and drain poorly, or it may be loose and unable to hold water. Additionally, garden soil may contain disease organisms, weed seeds, and insect eggs.
Soilless mixes usually consist of peat moss, perlite, and vermiculite. These ingredients ensure that the growing medium is light and airy and that it holds water while draining well. However, soilless mixes don’t have any nutritional component. To provide some nutritional support for plants and to introduce microbial activity, add compost to a soilless mix.
A mixture of 2 parts soilless mix and 1 part screened compost provides a high-quality environment for plants. If you want to include garden soil, a suitable mixture consists of equal parts of garden soil, screened compost, and sand.