Portulaca, including the ornamental Moss Rose (P. grandiflora) and the edible, weedy Purslane (P. oleracea), is known for its resilience in hot, dry conditions. Despite this hardiness, the plants have specific weaknesses that can frustrate gardeners. Understanding these common problems, ranging from pest infestations to cultural issues and safety concerns, allows for targeted interventions to maintain healthy growth or manage unwanted spread.
Common Pest and Disease Threats
Portulaca can occasionally host several sap-sucking insects that weaken the plant. Common pests include aphids (small, black or green insects clustering on new growth) and spider mites (leaving fine webbing and causing a stippled, pale appearance on foliage). Mealybugs, which resemble tiny, white cottony masses, also feed on succulent stems, drawing nutrients and causing stunted growth. Treating these pests often involves non-chemical methods, such as dislodging them with a strong jet of water or applying horticultural oil or insecticidal soap.
Fungal and bacterial issues arise from environmental conditions that are too moist for the plant’s succulent nature. The most frequent disease is root or crown rot, which manifests as mushy, blackened stems near the soil line due to overwatering or poorly draining soil. To prevent this, ensure the planting medium is sandy and fast-draining. Avoid excessive humidity to prevent surface fungi like powdery mildew, which coats leaves in a white film. Removing and disposing of diseased plant parts immediately helps prevent the spread of pathogens.
Failure to Bloom and Cultural Stressors
The most common reason for a lack of Portulaca flowers is insufficient sunlight, as the plants require a minimum of six to eight hours of direct, unfiltered sun daily. The blooms are heliotropic, meaning they only unfurl their petals when exposed to bright light, often remaining closed on cloudy days or in the shade. Inadequate light causes plants to divert energy into vegetative growth, producing lush, leafy foliage instead of flowers.
Improper watering and nutrient management also inhibit flowering. While Portulaca is drought-tolerant, overwatering is detrimental, leading to waterlogged roots and yellowing leaves. Allowing the soil to become excessively dry for prolonged periods stresses the plant, forcing it to conserve energy instead of producing flowers. Applying fertilizers high in nitrogen encourages leaves and stems rather than buds, so using a low-nitrogen fertilizer or avoiding fertilization entirely in lean, sandy soil is recommended.
Managing Unwanted Spreading
Portulaca, particularly the weedy Purslane variety, can become a nuisance due to its reproductive strategies. The plant is a prolific self-seeder, with a single plant capable of producing hundreds of thousands of tiny seeds that remain viable in the soil for years. Moreover, its fleshy stems are capable of vegetative propagation; even small fragments left on the soil surface can quickly develop roots and establish a new plant.
To manage this aggressive spread, consistent deadheading is the most effective preventative measure. When weeding or cultivating the area, remove the entire plant, including the deep taproot, and avoid breaking the brittle stems into pieces that can re-root. Establishing physical barriers, such as a garden edging buried several inches deep, can also help contain the lateral growth of the stems.
Safety Risks
A concern when growing ornamental Portulaca is its toxicity to household pets, specifically dogs and cats. The plants contain soluble calcium oxalates, which are compounds rapidly absorbed by the gastrointestinal tract when ingested. Once in the bloodstream, the oxalates bind to systemic calcium, resulting in a sudden drop in blood calcium levels, known as acute hypocalcemia.
The formation of insoluble calcium oxalate crystals can accumulate in the renal tubules, potentially leading to acute kidney failure in severe cases. Symptoms of ingestion include vomiting, diarrhea, lethargy, and tremors. While the common weed Purslane (P. oleracea) is often consumed by humans, it still contains these oxalates and should be kept away from pets.