While cacti are plants that are famous for surviving neglect they do benefit from repotting every so often and when it comes to repotting, cacti are plants that can sometimes be hard to judge. While these plants can be repotted at any time of the year now is a good time as we are coming to the end of the growing season.
By their nature the roots of cacti tend to be quite small in proportion to the size of the plant. A cactus should only be repotted into a larger pot when it has completely filled its old pot with roots. This will usually be about once a year for the first couple of years and then about every three years as the plant matures. When repotting it is usually a good idea to invest in specially mixed compost for cacti, as this will be well drained and have the right level nutrient to keep your plants healthy. While some people use peat based potting composts, over time these can lead to problems with drainage.
One of the main problems that you will face when repotting your cacti is the spines. This handling problem can be overcome however by either winding a collar of rolled up newspaper around the plant and using this as an improvised handle or by using fire side tongs to help maneuver the plant.
To repot simply lift the plant out of its original container using your makeshift handle. If the plant is reluctant to come out of the pot you can give it a gentle shove by pushing a pencil up through the drainage holes. When you have taken the plant out of the pot examine the roots for any obvious signs of damage. If the plant has been in the same pot for a couple of years it is usually a good idea break away any loose soil from around the top and sides of the root ball as this will have become caked and stagnant. Place the plant into a pot one size bigger making sure that you have grit in the bottom for drainage. Firm the soil around the root ball using a spoon so as not to hurt yourself on the spines. Allow the plant to settle in its new home for a couple of days before you start watering again.