Black Cactus

Black Cactus (Lobivia arachnacantha, now usually listed as Echinopsis arachnacantha) is a small clumping Bolivian cactus that stays around 12cm high and 30cm across. Broad yellow to orange blooms nearly as wide as the plant itself open in flushes through the warm months.

Why you'll love it

• Flowers out of all proportion. Large, silky and vivid on a plant this small.
• It builds into a colony. Offsets form around the base, so one head slowly becomes a clump 30cm across.
• Heat and drought are not a problem. Drought tolerant, heat tolerant and content in poor soil.
• Very low maintenance. No pruning, no feeding schedule, and long stretches where the correct action is nothing.

Where it works best

Pots and containers. A shallow terracotta or ceramic bowl is ideal: the roots are fine and shallow, and a deep pot just holds wet mix under them.

Balconies and courtyards. It takes reflected heat off paving and walls, which rules out most flowering plants.

Rockeries and gravel beds. In a raised gravel pocket where water runs straight through, it holds its shape and flowers reliably.

Growing Black Cactus in Australia

Position and climate. Full sun, with shelter from long wet spells. It suits arid and semi-arid, warm temperate, Mediterranean and subtropical gardens. It takes light frost only, so in cold districts keep it potted under cover through winter.

Soil. Sharp drainage matters most. Use a cactus and succulent mix, or a standard mix cut heavily with coarse sand, and top dress with grit to keep the base dry.

Water and feed. Water only when the mix has dried right through, roughly every two weeks in hot weather. Keep it dry over winter, which is when most losses happen. A weak low nitrogen feed in spring is all it needs.

Pruning. None required. If the clump outgrows its bowl, lift it in warm weather, twist off the outer offsets and pot them separately, letting the cuts dry for a few days before watering.

What to expect when it arrives

It is supplied in one size, a tube: a young single headed plant small enough to sit in your palm, and some seasons away from a full clump. Pot it into a 130mm to 150mm bowl of gritty mix on arrival, then leave it a fortnight before watering.

Plants are packed to travel dry and are delivered Australia wide, with delivery from $29.95. Expect slow growth, and the first flowers once it has bulked up. Every plant is covered by our 30 day healthy plant guarantee.

Plant care guides and related reading

• Browse the full cacti range
• Plants for balconies and courtyards
• A gardener's guide to succulents and cacti
• How to repot a plant properly

Common questions

How often should I water it?

Only when the mix is dry all the way through, usually every couple of weeks in summer. Give it nothing over winter: cold wet mix is what kills this species.

Will it flower in a pot?

Yes, and a pot is where most people grow it. Flowering follows a sunny position and a dry winter rest, so a plant kept too wet and too shaded will stay green.

How big does the clump get?

About 12cm high and up to 30cm across after several years of offsetting. It is slow, so expect a long lived small plant rather than something that fills a bed.

Can it live outside in a cold garden?

It tolerates light frost only. In cool districts keep it in a pot you can shift to a bright verandah for winter, completely dry.