I’m sorry I can’t tell you what kind of cactus this is but I’ve had it for several years and have seen the bottom of it turn brown. I was wondering what’s wrong with it and if there is anything I can do for it. Thanks so much for your help
Thank you for inquiring about your struggling cactus. The problem seems to be a combination of a few issues, which have likely compounded over the several years you have owned your plant.
Your photo shows the cactus by a window, without any apparent shade. There is a certain prevailing belief that all species of cacti can thrive under full, hot sun, as in a desert habitat. In fact, direct rays of the sun, day after day, can easily result in sun scorch, causing the plant tissue to burn, and scar. You can see the vertical ridges have burned more than the furrows. Your particular cactus does not have an abundance of spines, that, in some varieties, collectively, believe it or not, create a shading defense barrier against the burning rays of the sun. The outer cells have scarred and formed a hard crust as a result.
Next, looking at the relative size of the pot to plant mass, your cactus has likely become root-bound: there is not enough room for your plant to develop a healthy root system, robust enough to send moisture and nutrients up to the body of the plant, thereby exacerbating the sun burn damage.
As with most plants, over watering a healthy cactus can result in root rot — more water than the plant can send up above the soil level. However, whatever water you gave your cactus, in this condition, may no longer have been able to penetrate the tight mass of roots. For your plant, the best advice would be to re-pot in a special cactus planting medium (buy from a local nursery), according to the instructions, in a new, 30% larger clay (ie breathing) pot, with a water-catching saucer below. Then s-l-o-w-l-y water the plant over the following days, and weeks, to gently restore the root system to good operating condition. Give your cactus filtered light, continue to water in small, but regular, amounts, and patiently watch for encouraging signs of restoration and growth.
Please refer here to our TMG notes on REPOTTING A CACTUS
Also, please read our Toronto Master Gardeners guide to Growing Cacti and Other Succulents