What are the Common Causes of Rot in a Cactus?

Cactus do not require too much care and do well both indoors and outdoors

Many people grow cacti because they are easy to care for. If you forget to water them, you do not have to fret because your cactus does not need a lot of watering and feeding needs. However, fungus growth can happen with over watering and stem rot could result. Once you encounter stem rot, you might have to cut away at the brown parts of the stem and include some greenish areas as part of the cleaning process just to ensure the infection is not spreading further.

When your cactus is suffering from over watering, you will notice brown spots gathering on its stem. You should then un-pot your cactus and ensure that the roots are white and do not show any brown or black color. If there are brown and black roots, cut them away and leave the cactus to dry completely out of its pot. When using a knife, ensure that it is clean and sterilized as cacti are sensitive and rot can happen with unclean cuts. When handling stem rot or even grafting rot, you must cut away the rot as well as part of the green which may contain the infection. If you only cut the brown section of the body part that shows the rot and not the greenish section above the brown stem which could show some signs of infection, you could still be dealing with rot and all this can spread to the cactus’ cortex very quickly.

When you have treated your cactus and allowed it to dry out, repot the plant and watch the watering. Only water the cactus sparingly about 1-2 inches on the top soil and avoid leaving it in a saucer of water. Your cactus will thrive in the driest condition and needs only some water every 10-14 days.

So, what are the common causes of rot in a cactus? Some of these may include the following:

Fungus and Rot:

Exposure of the weakened plant stem can sometimes lead to infection and rot. Most often, fungi can attack an exposed and weakened part of the cactus and they spread rapidly through spore generation.

Insects and Invertebrates:

The cactus plant attracts many insects and rodents including birds which enjoy eating these plants. This problem is inherent usually with cacti planted outdoors. These critters do not feast on the whole plant but could leave open wounds and waste products about exposing your plant to plant pathogens. In some cases, the rodents are known to contently munch at your cactus until it is finished. Insects which feast on cacti include mealybugs, worms, caterpillars, red spider mite, aphids and nematodes.

Do not transport multiple cacti together as they could scar each other

Excessive moisture:

Cacti are succulents and generally store water in their tissue. In long dry conditions, they would use the water to help them survive. When we keep them over-watered, they have difficulty getting rid of the excess water in their stems. These cacti then swell up a lot with constant watering and there will come a time when the cactus will split open in one or more places. While a cactus may recover from this, it exposes the plant to rot and the roots begin to show signs of the rot. Sometimes, the whole plant will turn to mush.

Rapid Growth caused by Fertilizer:

Although indoor cacti may require some fertilization to encourage healthy growth and flowering, too much fertilizer can result in bloated plants and quick growth causing the stem to elongate and get distorted. Generally, cacti which are growing outdoors do not require any fertilizer as they are content with the outdoor sun and rain. Rain water for instance will provide enough nutrients for the soil. Instead of fertilizing, it is sometimes better to replace worn out soil with fresh soil to promote better root growth and replenish the much needed nutrients.

Physical Damage:

Cactus growers need to be careful when moving their plants about as sometimes they could damage the plant causing a scrape wound, a poke or in severe situations, a smash that could happen leading to a tear in the stem. Avoid carrying multiple potted cacti about as sometimes the spines from one cactus could puncture or scratch the other cactus next to it causing a brown scar to develop after a few days. This scar will remain with the plant for life and is sometimes mistaken as a sign of a disease or that a pest is near.

Sun Burn:

If you move your cactus plant from a shady location to direct sunlight, you could cause the plant to suffer from sun burn. Too much sun will cause the outer cells to die providing an impetus for fungi attack. A light burn will show up as a whitish discoloring on the exposed areas while more severe burns will take the color of a hard brown scar along the plant. If your cactus plant suffers at the whitish discoloring stage, you can undo the damage by getting it shade but if the plant bears a hard brown scar, the damage is permanent. Generally, a cactus which has been sitting under shade for a long time does not do too well under the sun and so, exposure to the sun should be a gradual affair.