I purchased this cactus recently and he is starting to turn brown. I’ve been told that this might be due to too much water or not enough sunlight. Additionally, I’ve been told that my pot should be draining. I would love some expert insight into the problem. Thank you!
The advice given to you so far has been fairly accurate. Specific cacti have different growing requirements, however, all cacti need to be planted in a good quality cacti potting mix, in a pot or container with drainage holes. I have noticed many small cacti being sold in tiny pots with no drain holes. They look very cute, but haven’t been sold with the plants health or longevity in mind.
Cacti potting mix is coarser than indoor plant potting mix. It contains a blend of ingredients that allows water to drain freely to the base of the pot. It has large air pockets between particles to allow the roots to breathe and to dry out in between watering- which cacti like, as it imitates native growing conditions.
I can see white lumps in your potting mix. That may be pumice, perlite or vermiculite- which is ideal. If they are small beads of styrafoam your cactus has been planted in potting mix for indoor plants. This mixture is designed to keep the soil moist, which can be detrimental to cacti. It also contains more nutrients and fertilizer than most cacti need. Pick up one of the white beads in the soil and squeeze it to see is it is solid or soft. If you can compress it, your cacti will need repotting. I have attached a link below to our Toronto Master Gardeners Cacti Growing Guide for your reference. Note the watering guidelines and useful references at the bottom of the article.
Cacti love sunlight and in Toronto do best near a south or west facing window. Be mindful that, despite many types of cacti being desert dwellers in their native range, they don’t do well on our extreme heat days if they are exposed to extended periods of full sun during the heat of the day. They can actually get sunburnt. The area on the leaf pad, or cladode, that receives intense rays of sunlight and heat can burn resulting in the green tissue drying up, turning white to grey brown and making the plant susceptible to fungal diseases.
Sunburn will appear as a dried pale brown patch, with the underlying tissue remaining firm. Move the plant away from intense heat and light, but remember to move it back after the heat wave has past. Sunburnt cacti don’t look great, but can continue to grow and thrive if all of their ideal growing conditions are met.
The sunburnt area will not turn back to green, so ultimately you may decide to use the damaged leaf pad as the parent plant for propagating new plants. In your case the damage is on the parent plant, so cutting out the damaged area could injure the cladodes attached to the parent, also known as ‘pups’. If the damage was on a pup you could remove it with a clean sharp blade just above the point of attachment and discard- or use to propagate new plants.
Your cactus appears to be from the Opuntia family, which includes the Prickly Pear. If Opuntia are stressed by intense heat conditions they are susceptible to a fungus called Hendersonia opuntiae. There is no treatment for this disease. The damaged areas are cut out until healthy green tissue is seen or the entire cladode is removed. Because of the location of your damage, the cladodes attached to the damaged piece would need to be removed and propagated and the infected cladode discarded into a garbage bin (not your compost bin)
To diagnose a Hendersonia fungal infection, check if the damaged brown area on your cactus feels soft or soggy. Did you notice multiple patches of die back that joined together to become one large patch? Were the edges of the damage reddish brown at first, then turned to pale grey brown? If so, it is most likely infected.
I am really hoping that it is just sunburn!
Good luck with saving your cactus.
15 Sept 2022