|I have a rare cactus species (I don't know the name) and I want to propagate it through cutting some of the stems and rooting them in soil. Do you have any special recommendations for this procedure? Thank you.|
|Propagation of cacti through cuttings provides larger plants much more quickly than propagation from seed, but far fewer plant can be obtained. Those types of cacti that are columnar, pad-forming or those with segmented stems such as a Christmas cactus are easily started from cuttings. As with seed, spring is the best time to take cuttings, as most cacti will be emerging from their winter rest at this time and initiating new growth. The size of the actual cutting taken can be quite variable. On a Christmas cactus, a couple of stem segments may be used, with a total length of a few centimetres, while on some columnar cactus plants, a single cutting may be as long as a meter. An important point is that the plant that you are taking the cutting from should be in as healthy a condition as possible.
When taking a cutting from a stem section, use a clean sharp knife. If you are taking several sections from one long stem, you must remember which was the top and the bottom of each piece, because a stem piece that is planted upside down will not grow. A simple way of keeping track of the top and bottom is to cut the bottom of each segment on a slight angle, and the top straight across. For pad-forming, or branching cacti, the cuttings should be taken at the joints so that the mother plant is not significantly disfigured. A single oval pad from a pad-forming cactus makes an ideal sized cutting.
The primary problem encountered with cactus cuttings is the development of fungal soft rot. This condition begins at the cut surface and eventually reduces the entire cutting to a slimy mass. Two techniques are recommended for avoiding this problem. The first is to simply allow all fresh cuttings to sit in a warm dry place for from 1 to 14 days before they are placed in the rooting medium; the larger the cut surface, the longer they should be allowed to dry. During this time, the cut moist surface will form a dry callus which is far less prone to rot. Although it sounds slightly alarming to leave a newly taken cutting sitting exposed for several days, remember that a cactus is able to survive periods of drought. As long as the cutting is not noticeably shrivelled, it is probably alright to leave it dry. Newly cut stem segments may also be dipped in garden sulphur before planting to prevent the onset of soft rot.
Cuttings will root in a standard well-drained cactus mixture if provided with bright light and cool temperatures for several months. Although the cuttings may not have a developed a root system, resist the temptation to keep their soil any wetter than you would a normal cactus plant. The wetter the soil, the more likely the cuttings will rot.
Best wishes with your cacti!