Germination temperature
About 21 °C (70 °F); 20-25 °C (68-77 °F) suits most species.
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Cactus growing guide
Sow small cactus seed on a clean, gritty mix, then balance humidity with daily ventilation and filtered light. Most kinds sprout in one to two weeks at about 21 °C (70 °F).
About 21 °C (70 °F); 20-25 °C (68-77 °F) suits most species.
Small seed on the surface; cover larger seed with grit no deeper than the seed.
Usually 1-2 weeks; prickly pears may take months.
Bright, out of direct sun; light helps many cacti germinate.
None for most cacti.
Sow in pots or trays; pot on when big enough to handle.
Use small pots or trays and label the species and sowing date. Mix very small seed with a little clean sand for more even sowing. Sterilising the compost is optional but reduces rot: about an hour in the oven or three to four minutes in a microwave.
Not needed for most cacti. Some Opuntia (prickly pear) species have hard seeds with built-in dormancy; nicking the coat or washing the seed helps, and germination can still take months.
Not needed for most cacti. A few cold-climate Opuntia species need a cold, moist period.
Not needed. Small seed is hard to spread once wet; moisten the compost before sowing instead.
The RHS keeps cactus seed trays at about 21 °C (70 °F). A review of cactus germination found 20-23 °C (68-73 °F) works well across many genera, with optima often near 25 °C (77 °F); germination is poor below about 12 °C (54 °F). A drop to about 15 °C (59 °F) at night is fine. In India sow in late winter to spring or after the monsoon, when it is warm but not humid.
Leave small seed uncovered: many cacti need light to germinate. Cover larger seed lightly with grit, no deeper than the seed is thick, or sow onto a thin grit layer and wash the seed in with a fine spray.
Peat-free seed compost, sieved if coarse, with about a third horticultural grit, sharp sand or perlite. A grit top dressing holds seed in place and discourages moss and algae.
Moisten by standing the pot in water to half its depth or with a mister, then drain. Cover with glass or clear plastic, or put the pot in a clear bag. Keep the compost moist but not soggy.
Bright but out of direct sun. A covered tray can overheat quickly and scorch young seedlings.
Most cactus seed germinates within one to two weeks, but germination is often sporadic, so keep the pot going for several weeks. Opuntia (prickly pear) and its relatives may take a few months.
Lift the cover and remove condensation daily while maintaining even moisture. Once seedlings are growing well, open the bag or cover a little more each day.
Move seedlings only when they are large enough to handle without damaging their small root systems, or when they start to crowd each other. This can take up to 12 months: in the same year for fast growers and the next year for slow ones. Lift the compost in one piece and tease the roots apart.
Cactus seedlings usually take six to twelve months to reach the size of a pea, then grow faster. New seedlings need steadier moisture than mature cacti, while still requiring air and drainage.
Cause: mould or damping off in a wet, closed tray. Fix: use clean compost, ventilate daily and apply a copper-based fungicide after sowing.
Cause: a constantly wet surface without grit. Fix: top-dress with fine grit and avoid overwatering.
Cause: direct sun under a cover. Fix: shade the tray, keep it bright but out of direct sun, and accustom plants to sun gradually.
Cause: seed buried too deep, too cool, or a slow kind such as prickly pear. Fix: keep small seed on the surface at about 21 °C (70 °F) and be patient with Opuntia.
Cause: mealybugs or root mealybugs. Fix: remove them, wash roots and repot in fresh compost; these are insects, so fungicides do not help.
Once plants are established, water thoroughly when the compost surface feels dry and never leave pots standing in water. In winter water only enough to stop shrivelling.
Most cacti need bright light, such as a sunny windowsill; in shade they stretch. Forest cacti such as Schlumbergera and Epiphyllum prefer semi-shade.
Grow on in a free-draining, gritty cactus compost, for example two parts loam-based compost to one part grit. Feed monthly in the growing season with a high-potassium liquid feed.
Repot in spring when roots fill the pot, about every 2-3 years, and avoid oversized pots, which hold too much wet compost.
Raise your own cacti from seed on a bright, warm windowsill.
Leave very small seed uncovered, since light helps many cacti germinate, and cover larger seed lightly with grit. Follow the packet when it gives species-specific depth.
No. A clear cover helps retain humidity, but the RHS advises daily ventilation and removal of condensation.
Most sprout within one to two weeks at about 21 °C (70 °F), though germination is often sporadic. Prickly pear (Opuntia) seed can take months.