If brown spots spread on a cactus, this damage can be traced back to various causes. In most cases, mistakes in care are responsible for the dilemma. Diseases or pests are less common. We have put together the most common causes for you here with tips for the right course of action.
What causes brown spots on cacti?
Brown spots on cacti are often caused by care errors such as lack of nutrients, waterlogging, incorrect overwintering or sunburn. Sucking pests such as spider mites, scale insects or aphids can also cause this. Natural corking occurs in some cactus species as they age.
These care mistakes cause brown spots
Cacti react to failures in the care program with, among other things, brown spots on the prickly epidermis. This applies to an unsuitable choice of location as well as an unbalanced water and nutrient balance. The following overview summarizes common causes:
- Nutrient deficiency: Fertilize cacti every second watering from May to September
- Waterlogging: Allow the substrate to almost dry out during growth and then water thoroughly
- Wrong wintering: From November to February, keep it bright and cool at 5 to 12 degrees and do not water it
Although cacti are sun worshipers, they can still suffer from sunburn. If the plants move to their original location in full sun on the windowsill after the winter, they should first acclimatize in a partially shaded location for 8 to 10 days. This precaution is also relevant if you put your cacti on the balcony in May.
Sucking pests leave brown spots
If negligence in care can be ruled out as the cause of brown spots, you are most likely dealing with pest infestation. Stinging and sucking insects damage the epidermis, causing brown spots to develop there. Spider mites are also among the culprits, as are scale insects and aphids. Examine the affected cactus with a magnifying glass to locate the pests. In the early stages, the infestation can be combated with simple home remedies:
- Dab scale insects with alcohol-soaked cotton swabs or dust with diatomaceous earth
- Spray spider mites and aphids with the classic soft soap solution (€9.00 on Amazon)
By packing the infected cactus in an airtight plastic bag for 3 to 5 days, you cut off the pests and their brood from the oxygen supply.
Tip
As cacti get older, various types tend to become corked. This is a natural process during which the tissue becomes woody, which can be recognized by brown spots. Young cacti, on the other hand, react to excessive humidity by corking and watering with cold, hard tap water. In addition, epidermis becomes corked when the cactus suffers from sunburn.