How to Root a Columnar Cacti

Use a sharp knife to cut a piece from a healthy columnar cacti. You may wish to wear heavy gloves to avoid injury from the cacti needles. Make the cut at a 45-degree angle so water or rain is less likely to enter the mother cacti and cause it to rot. After you have removed the piece, recut the bottom end so it is level or flat.

Harden off the cut end of the cacti cutting by first coating the cut end in garden sulphur, which helps protect the exposed end from pathogens. After the sulphur dusting allow the cut end to air-dry until a hard callus has formed. The callus will protect the cutting from rotting. It may take several weeks for the callus to develop completely. You can either prop the cacti cutting vertically in a container to keep it straight, or lay it on its side, rotating it every few days so it will not bend or curve. The cutting should not be placed in direct sunlight while the cut end hardens.

Mix 50% perlite to the cacti potting soil. The perlite addition is needed to add aeration and water drainage to the soil medium while the columnar cutting is developing roots. Place the new cacti-perlite mix into your large planter.

Plant the columnar cacti cutting deep into the potting mix -- 1/3 to 1/2 of the cacti should be in the soil. This will help keep the cacti stable and upright.

Water the planted cutting when the soil medium becomes slightly damp, but do not overwater. Place the potted columnar cutting in a bright location, but not in direct sun. The cacti should develop a root system in about four to six weeks. When you see the cacti plump up and begin to grow at the top, this indicates that roots have developed and food and water are being taken up.