oxalis

Oxalis, commonly known as sorrel, is a highly persistent weed that frequently colonizes the pots of cultivated cacti. While it does not directly parasitize the cacti, it is considered a major nuisance because it is extremely difficult to fully eradicate once established. It spreads easily between collections, making it a near-universal presence among growers.

Oxalis is easily recognized as a clover-like green weed growing in the substrate at the base of the cactus. While it does not cause direct physical symptoms on the cactus itself, its presence is a strong cultural indicator. A proliferation of oxalis typically indicates that the potting medium is retaining too much moisture.

The weed is introduced through seeds or plant fragments, often shared inadvertently between growers when trading plants. Once present, it spreads rapidly. Its growth and survival are heavily favored by wet conditions, high humidity, and poorly draining soil mixes.

Eradicating oxalis completely is widely considered unfeasible, but it can be managed using the following methods:

• Manual Weeding: Regular weeding (several times a year) is required to keep the weed from overtaking the pot.
• Improving Drainage: To discourage oxalis growth, growers should increase the inorganic drainage components of their soil. Dave Crow suggests upping the pumice ratio in the soil mix, particularly during rainy periods, to prevent the substrate from holding moisture for too long.
• Coexistence: Some growers choose to tolerate the weed, viewing it as a source of organic matter, though it must still be managed to prevent it from crowding the cactus.

Community examples - the photos above belong to these reporters; credit them.

* Expert Participation: Gee Bee did not participate in this discussion. Therefore, there are no authoritative statements or guidelines from Gee Bee regarding this topic. * Nitrogen Fixation Claim: Gabe Rupe and Anthony Johansen asserted that oxalis acts as a “nitrogen fixer” that provides free nitrogen to the soil. This is a community belief and is not botanically verified for Oxalis species. * Indirect Hazards: Markula Leonhardt noted that pets (specifically cats) attracted to eating the weed may accidentally get injured by the host cactus's spines.

* Topic Authority: None (Gee Bee did not participate in this discussion). * Contributors: Jeremy Hanshaw, Ben Swallow, Dave Crow, Gabe Rupe, Anthony Johansen. * Photo Credits: Dave Crow.