Opuntia ROBUSTA

Opuntia ROBUSTA - Silver Dollar Prickly Pear, Wheel Cactus, Robust Prickly Pear, Opuntia robusta.

Opuntia is a large genus of succulent plants in the cactus family (Cactaceae), comprising about 150-180 species distributed in the New World from Canada to South America. In the wild, members of the genus occur in deserts, semi-deserts, dry savannas, prairies, woodlands, on rocky slopes, sandy plains, and other open habitats with bright sun and well-drained soils.

The plants usually grow as shrubby, creeping, or tree-like cacti with flat jointed stems called cladodes or segments. Leaves in mature plants are reduced; photosynthesis is performed by green fleshy stem segments. The areoles bear spines and small barbed bristles - glochids, which detach easily and irritate the skin.

Flowers in prickly pears are large, diurnal, usually yellow, orange, reddish, or pink, forming along the margins of mature segments. After pollination, fleshy fruits develop, often brightly colored and edible in many species. The seeds are hard, dense, enclosed in the fruit pulp, with a pronounced coat, which often results in protracted germination.

Robust prickly pear has nearly geometrically circular segments covered with a gray bloom. Widely spaced areoles are sometimes equipped with yellow or whitish spines. Flowers are yellow, reddish on the outside.

Opuntia seeds are medium-sized for cacti, light beige or yellowish-brown, rounded, flat-rounded, or slightly irregular in shape, with a dense, hard coat. To accelerate germination, very light mechanical scarification with sandpaper or careful filing of the seed edge without damaging the embryo is permissible. Seed germination rate under careful greenhouse conditions is typically around 50-80%.

Sowing is carried out in spring or year-round with stable supplemental lighting. A sterile, fine-grained mineral substrate based on sifted cactus soil, fine sand, perlite, and mineral grit is used. Seeds are distributed on the surface, pressed lightly into the damp soil, and covered with a thin layer of fine sand about 1-2 mm (0.04-0.08 in) thick. The sowing is moistened with a spray bottle using a weak solution of potassium permanganate or biofungicide with the addition of a growth stimulant: SUPERthrive, HB-101, Aminosol, Epin, or Zircon. The container is covered with a transparent lid or placed in a propagator.

Germination is carried out under bright diffused light at a temperature of about 24-28 °C (75-82 °F), without direct overheating under the sun. The surface is kept moderately moist but not wet, moistening performed only by fine spraying. Sowing containers are ventilated daily and condensation is removed, as stagnant moisture is hazardous to prickly pear seedlings and rapidly causes fungal infections.

First seedlings may appear in 10-14 days; the usual germination period is 2-6 weeks, and the maximum possible period under a hard seed coat, temperature fluctuations, or partial drying of the surface can stretch to 2-3 months. After emergence, the cover is gradually opened, and seedlings are kept in bright diffused light with careful moistening. Prick-potting is carried out after noticeable strengthening of the plants and the formation of the first small segments, with minimal damage to the roots.

© Greeniverse. All rights reserved.

For cultivation, select the brightest possible location with direct sunlight for most of the day. South, southeast, and southwest windows, open sunny balconies, and well-ventilated terraces are best suited. Under insufficient light, the segments stretch out, becoming thin, soft, and less resistant to watering.

During the period of active growth, maintain a temperature of about 22-30 °C (72-86 °F) with good air movement. The plant tolerates heat and dry air provided the roots are not in overheated wet soil. Wintering is kept bright, dry, and cool, around 5-12 °C (41-54 °F). During cool maintenance, watering is almost completely suspended, since wet substrate combined with low temperature quickly leads to rotting of roots and the base of segments.

Watering is carried out moderately, only after the substrate has completely dried out. In spring and summer, the soil is moistened in small portions, always draining water from the drip tray. In autumn, watering is gradually reduced, and in winter the plant is kept almost completely dry. Misting is not required, and water coming into contact with areoles and segment joints is undesirable under poor ventilation.

Use a very loose mineral substrate for cacti with a high content of coarse sand, fine stone chips, pumice, zeolite, perlite, or other inert aerators. Organic matter is added moderately. A tall drainage layer is placed at the bottom of the pot, and a stable, heavy, not overly deep container is chosen, with mandatory drainage holes.

Fertilizer is applied only during the period of active growth, once every 4-6 weeks with a weak solution of fertilizer for cacti and succulents with reduced nitrogen content. Excess nutrients cause watery loose growth and reduce resistance to rot. Repotting is carried out in spring as the pot fills with roots; after repotting, the plant is kept without watering for several days. When handling the plant, use thick gloves or tongs, as glochids easily detach from the areoles.