Q. What kind of potting mix should I use for my cactus?
A good starting ratio for a cactus potting mixture is a three-part mix: one-third compost, one-third horticultural-grade sand, and one-third grit.
For the compost component, a growing number of hobbyists believe that a peat-based compost should not be used, as it seems to contribute to pest problems such as root mealy bug and fungus gnat, and doesn't contribute much in the way of nutrients to the plant. Many people start with a good grade commercial potting mix for the compost component, and some sift it through a screen to remove such "undesirables" as the small pieces of wood and twigs that can sometimes be found in such mixes.
All sand is not created equal. The sand component should be horticultural grade, relatively coarse, and sharp. Never use non-horticultural grade sand, such as fill sand or beach sand, as this is usually not washed, and can contain, among other things, salt.
For the grit component, most people agree that horticultural pumice is the best. It is also not widely available, and can be expensive if you can find it. Some other materials that can be used include perlite, porous gravel, and lava fines. People often have good luck using fired clay products for the grit component. These products include certain cat litters and products that are used to absorb oil spills. If using one of the clay products, you must ensure that it is a fired clay that does not break down and turn to mush when it gets wet. Check the labeling, and to be sure to test it by putting some in a jar of water for some time to see if it breaks down. Mush in your potting mix will do your plants no good.
There are no hard and fast rules for potting mixes, so you'll need to experiment with ratios.
For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service