Hi. My cactus was doing well up until about about a month ago. It now has quite a few light brown areas. I wonder what I can do to restore it to its previous green health. Please see my photos. Thank you for your assistance.
Your plant appears to be an Opuntia (“prickly pear” cactus) that is living indoors. Toronto Master Gardeners has a Guide to Growing Cacti and other Succulents which provides general advice that can be helpful.
If you notice the pads of your Opuntia cactus turning light brown or white, it could be a sign of various issues. Here are some common causes and how to deal with them:
- Sunburn: Opuntia cacti need plenty of sunlight, but too much direct sunlight can cause sunburn, which appears as white or light brown spots on the pads. Move the cactus to a location with indirect sunlight or provide some shade during the hottest part of the day. Gradually introduce it to more sunlight to avoid shock.
- Overwatering: Overwatering is a common issue with indoor cacti. Make sure your Opuntia is planted in well-draining soil, and allow the soil to dry out completely between waterings. Water sparingly, especially during the winter months when the cactus is dormant. If the soil is consistently wet, the roots can rot, leading to discoloured pads.
- Fungal Infections: White or brown spots can also be caused by fungal infections. To prevent this, ensure good air circulation around the plant and avoid splashing water on the pads when watering. If you suspect a fungal issue, remove the affected pads and apply a fungicide to the remaining plant.
- Pests: Pests such as scale insects or mealybugs can infest Opuntia cacti, causing damage and discolouration. Inspect the cactus carefully for any signs of pests, and if you find any, remove them manually or use insecticidal soap to control the infestation.
- Nutrient Deficiency: A lack of essential nutrients can lead to discolouration in cactus pads. Fertilize your Opuntia with a balanced, diluted cactus fertilizer during the growing season (spring and summer). Follow the recommended dosage on the fertilizer label, and avoid over-fertilization.
- Cold Damage: Opuntia cacti are generally hardy, but they can suffer damage from extreme cold. If the cactus is exposed to low temperatures below its tolerance level, it can develop discolored spots. Protect your Opuntia from frost and cold drafts during the winter.
- Physical Damage: Sometimes, physical damage to the pads, such as scarring or bruising, can lead to discolouration. Avoid touching or handling the cactus unnecessarily, and be cautious when repotting or moving it.
- Bacterial/fungal disease: While less common, Opuntia cacti can be susceptible to bacterial or viral infections. I’ll point you to the Texas A&M Agrilife Extension which has an extensive list of diseases affecting cacti.
I’ll also point you to a past Toronto Master Gardeners post which dealt with the issue of a discoloured Opuntia. You’ll find similar advice as above. Best of luck with your cactus.