Gardening Guides - Techniques - Repotting A Cactus - BBC

About cacti

Cacti come in all shapes and sizes, textures and flower colours. There are two main groups of cacti - the desert cacti (usually covered in spines), and the jungle or rainforest cacti (often without spines and most are epiphytes). Choose the right cactus for the right spot and you'll have a trouble-free, interesting houseplant that'll last for years.

When to repot

Cacti should be repotted as soon as the roots begin to show through the drainage holes at the bottom of its pot. As a general rule, fast growing species should be repotted every two to three years and slow growing species every three to four years. Repotting is best carried out in the spring, when cacti are enjoying active growth. Water the cactus two days before repotting, so the roots are moist but not saturated.

What to do

How to repot

• Most cacti have sharp spines, so it's important to wear gloves or take other protective measures when handling these plants.
• Gently remove the cactus from its pot and discard any topdressing.
• Carefully check the roots for pest and diseases, cutting out any roots that are dehydrated or dead and adding a fungicide if necessary.
• Choose a new container, one size larger than its original, and place a layer of drainage material (washed gravel or broken crocks) in the base.
• Add a well-draining and slightly acidic compost with a pH of 4 to 5.5.
• Repot the cactus to its original depth and gently firm in the compost.
• Trickle a thin layer of grit or gravel around the surface of the cactus which will help water to drain quickly.

Aftercare

• Make sure the plants are watered regularly throughout their growing season in spring and summer. Moisten the soil thoroughly, allowing it to almost completely dry out before watering again.
• Water in the early morning or late in the evening, as plants may scorch if they're covered in water droplets during the heat of the day.
• Plants in pots may also be watered by placing the container in a shallow pan of water. Lift the container from the water to drain as soon as the surface of the compost appears moist.
• In October, when days shorten, light grows poor and growth subsequently slows. Stop watering all cacti and allow them to go dormant for the winter months. They should only be watered if temperatures rise above 10°C (50°F).
• Cacti need little maintenance in order to thrive, but adequate light, warmth and ventilation are all essential for healthy growth. Most cacti are suitable for sunny south or west-facing windowsills where they receive high light levels and are protected from frost. Plants should be kept at around 27°C (81°F) during the day and at around 13ºC (55°F) in the evening.

Five to try

• Opuntia microdasys var. albispina - a desert cactus that thrives in a warm, dry spot
• Echinocactus grusonii - a golden, spiny cactus that needs to be handled with care!
• Rebutia minuscula - a spiny, mountain cactus which has bold red-orange flowers
• Mammalaria microcarpa - a large desert cactus with unusual red spines
• Cleistocactus strausii - this hardy cactus grows vigorously and needs repotting annually