Bishop’s cap

Bishop’s cap: how do you recognise it?

Habit

Globular, later shortly columnar, up to 20–25 cm tall in a pot; rarely branches.

Ribs

Usually five, sometimes three, four or more, broad and sharply keeled.

Skin

Grey-green and densely covered in tiny white woolly flecks. No spines, only woolly areoles along the rib edges.

Flower

Pale yellow and silky, 4–6 cm across, on top of the plant from June to August. Each flower lasts a few days.

Roots

Fine and sensitive to wet feet: in wet compost they rot quickly.

Flowering: June–August · Plants: March–April

Why grow it?

• An exceptionally elegant, symmetrical shape, with no prickly spines.
• Large, silky yellow flowers in summer, even on fairly young plants.
• Little work: it rarely needs water and tolerates dry indoor air.
• Ideal for a sunny windowsill, where many other house plants scorch.
• Stays small and is happy in the same pot for years.

Bishop’s cap: where does it grow best?

• As sunny as possible: a south or west window. In summer it can also go outside in a sunny spot under cover, sheltered from rain.
• Get it used to full sun gradually in spring, or the skin will scorch.
• Very open, mineral cactus compost with coarse sand, grit or lava granules; it is happy with a little lime.
• Warm in summer, cool and dry in winter at 5–10 °C.

Light

Sunny

Potting soil

Cactus compost

Acidity

Neutral or chalky

Watering

Sparingly

Size

0.25 m tall, 0.2 m wide

Temperature

Minimum 5 °C

Goes well with

• Old man cactus: Wants the same sun, dry compost and cool winter.
• Mammillaria: Small cushion cacti that also flower freely on the windowsill.
• Echeveria: Grey-green and pink rosettes as a soft counterpart.
• Living stones: Just as frugal with water and lovely in a shallow bowl.

Bishop’s cap: when and how to plant it?

Plant in March–April.

1. Repot in March or April, every two or three years, when the plant fills its pot.
2. Choose a pot that is not too big, with a drainage hole; terracotta dries out faster.
3. Mix cactus compost with a third to a half of coarse sand, grit or lava granules.
4. Hold the plant with a rolled-up newspaper or thick gloves and set it at the same depth as before. A layer of grit keeps the base dry.
5. Repot into dry compost and wait a week before watering, so that damaged roots can heal first.

Care

Water

From April to September water only when the compost is completely dry, then thoroughly, and empty the saucer. Too little is better than too much.

Feeding

During the growing season, cactus feed at half strength once a month.

Winter rest

From November to February completely dry, cool (5–10 °C) and bright: it will flower better.

Skin

Do not touch the white flecks or spray the plant: flecks that rub off do not grow back.

Repotting

Every two or three years in spring, always into dry compost.

Tip: Give it a proper winter rest: dry and cool at 5–10 °C. That keeps it compact and makes it flower far more freely the following summer.

Bishop’s cap: when to prune it?

When: Bishop’s cap is not pruned.

How:

• Gently remove dried, spent flowers from the top, so that no moisture or rot lingers there.
• Clear dirt and debris from the crown with a soft brush.
• Cut a rotten patch well back into healthy tissue and let the wound dry thoroughly.

Pruning calendar and basic rules

Propagation

Seed

The usual method, as it rarely produces offsets. In spring, sow fresh seed on moist, fine cactus compost without covering it, under glass at 20–25 °C. The seedlings grow slowly.

Grafting

Enthusiasts sometimes graft young seedlings onto a vigorous rootstock to speed up growth; this takes some experience.

Bishop’s cap: how does it get through the winter?

• House plant: it cannot take frost and needs at least 5 °C.
• From November to February keep it completely dry, cool (5–10 °C) and as bright as possible, for example in an unheated room.
• A warm, wet winter makes it soft and prone to rot, and costs flowers.
• In March, start carefully with a very little water again.

Diseases and pests

• Rot: Soft, brown or black patches at the base from overwatering or cold, wet compost. Cut well back, let it dry and replant in fresh, dry compost; water more sparingly from then on.
• Mealybug: White fluffy tufts in the crown or on the roots. Remove with a brush dipped in methylated spirit; for root mealybug, repot and rinse the roots clean.
• Sun scorch: Brown, corky patches after a sudden move into full sun. Let it adjust gradually every spring.
• No flowers: Usually caused by a winter that is too warm or wet, or by too little light. Give it a cool, dry winter rest and a sunny summer spot.

Through the year

• January: Leave it dry, cool and bright.
• February: Still no water. Prepare a sunny spot.
• March: Carefully start watering a little. Repot if needed.
• April: Get it used to full sun gradually. Water when the compost is dry.
• May: Cactus feed once a month. Possibly outside under cover.
• June: Flowering. Water when the compost is completely dry.
• July: Flowering. Remove spent flowers.
• August: Last flowers. Last feed.
• September: Water less. Bring it in before cold nights.
• October: Very little water. Move it somewhere cooler.
• November: Winter rest: dry and cool at 5–10 °C.
• December: Leave it dry and bright.

Did you know?

• The name Astrophytum means ‘star plant’ and myriostigma ‘with countless dots’, after the white flecks.
• Unlike most cacti, it has no spines at all.
• Enthusiasts grow countless forms: with four or eight ribs, without flecks or with extra-dense white flecks.