The Acosta plant, scientifically known as Pleurothallis purpurea, is an intriguing orchid. This guide covers its cultivation and care.
Understanding the Acosta Plant
The “Acosta plant” is scientifically Pleurothallis purpurea. “Acosta” is an older, defunct classification; the species now belongs to the large Pleurothallis genus, which has over 1,200 species. These orchids are often called “bonnet orchids” and abbreviated as “Pths” in horticulture.
Pleurothallis purpurea has slender, ribbed stems and small, leathery leaves, often heart-shaped to aid water capture. Its flowers are diminutive and can display various colors, though purpurea indicates a purple hue. These orchids are primarily found in the New World, especially in the humid cloud forests of Central and South America’s Andes.
Acosta Plant Care Requirements
Pleurothallis purpurea thrives when its specific needs for light, water, humidity, and temperature are consistently met.
Light
Pleurothallis purpurea prefers low to intermediate light, thriving in bright, indirect conditions. Direct, intense sunlight causes leaf scorching, turning leaves brown or yellow and brittle. An ideal light intensity for most Pleurothallis species ranges from 700 to 1500 foot-candles.
Watering
These orchids must not dry out completely. Water the plant as its potting medium approaches light wetness, keeping it consistently moist but not waterlogged. In high humidity, daily morning watering is sufficient; in drier conditions, more frequent watering or misting is necessary. Use water low in alkalinity, such as rainwater, distilled water, or reverse osmosis water.
Humidity
High humidity, with a minimum of 70%, is vital for Pleurothallis purpurea. Maintain humidity using:
A humidifier
A humidity tray
An orchidarium
A terrarium
Ensure roots do not sit in standing water to prevent rot.
Temperature
Pleurothallis purpurea prefers cool to intermediate temperatures. Day temperatures should be 65-75°F (18-24°C), with night temperatures dropping to 40-60°F (5-16°C). Consistent temperatures above 70°F (21°C) cause stress and shriveling, especially with insufficient humidity. A 9-18°F (5-10°C) day-night temperature difference promotes healthier growth.
Potting Medium
A well-aerated potting medium that retains moisture while draining thoroughly is best for Pleurothallis orchids. Options include fine fir bark, New Zealand sphagnum moss, or a mix of perlite and charcoal. These plants also grow mounted on bark slabs or twigs, often with sphagnum moss around roots for moisture retention. Check for mix decomposition every 9-12 months; repot if the medium breaks down.
Fertilization
Orchids are light feeders, and Pleurothallis purpurea benefits from weak, balanced orchid fertilizer. When potted in sphagnum moss, fertilize every third watering year-round. A balanced fertilizer (e.g., 10-10-10 N-P-K) applies every 4-6 weeks at diluted strength during the growing season. Use low-alkalinity water for fertilizer solutions to prevent mineral buildup.
Air Circulation
Good air circulation prevents stagnant conditions and fungal issues. While high humidity is desired, proper air movement helps prevent black spotting on leaves, especially during warmer periods. Place plants near a fan, ensuring it does not blow directly on them, to maintain gentle air movement.
Propagating Acosta Plants
Propagating Pleurothallis purpurea is primarily achieved through plant division. This method uses the plant’s natural habit of forming multiple growths along its rhizome. The best time for division is spring or early summer when the plant is actively growing.
Carefully remove the plant from its pot and gently untangle the roots. Examine the rhizome for sections with at least two or three growths, each with its own root system. Use a sharp, sterilized knife or scissors to cut the rhizome between these desired growths, making clean cuts near the base.
After division, prepare small pots with a well-draining orchid mix. Position each new plant so the rhizome is just below the substrate surface. Water the newly potted divisions thoroughly to settle roots, then place them in bright, filtered light. Consistent moisture and high humidity encourage root establishment.
Common Challenges and Solutions
Pleurothallis purpurea may encounter issues. Leaf discoloration, such as yellowing or browning, indicates improper watering or light. Yellow leaves signal overwatering, while brown tips suggest insufficient humidity or under-watering. Adjust watering frequency and ensure proper humidity. Leaves turning yellow and falling off also indicate inadequate light.
Lack of blooms or stunted growth stems from insufficient light or improper fertilization. Ensure the plant receives adequate indirect light and a consistent, weak orchid feeding schedule to encourage flowering.
Pleurothallis are susceptible to pests, including:
Scales
Mealybugs
Spider mites
Aphids
These sap-feeding insects cause chlorotic spots and weaken the plant. Fungal issues like black rot, brown rot, and leaf spotting also occur, often exacerbated by poor air circulation or overly damp conditions. Prompt identification and treatment are necessary. For pests, wash with soapy water or apply insecticidal soap. Improve air circulation and adjust watering practices to prevent fungal problems.