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Potting soil and repotting

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Repot Neobuxbaumia polylopha, when it is resuming its active growth
Photo: Jardin botanique de Montréal (Michel Tremblay)

Given the wide diversity of succulent plants, there is no one ideal recipe for potting soil, but most of these plants are fairly tolerant. The main features to look for are excellent drainage and good aeration, because standing water and a lack of air circulation in the soil are conducive to rot. Whatever potting soil you choose, it should not have a large proportion of organic amendments such as compost, manure or black earth. Tall specimens should be planted in soil that is dense enough to prevent them from toppling over. You can add coarse sand or gravel to increase the soil density.

Most commercial succulent potting mixes available on the market contain too much organic material and have poor drainage. It is best to amend them with coarse sand, gravel or perlite. You can also prepare your own soil by mixing 1/3 coarse sand, 1/3 perlite and 1/3 well-decomposed organic potting soil with a little compost. The medium should be slightly acid, with a pH of 5.5 to 6.5.

Spring is the best time to repot a plant, when it is resuming its active growth. Avoid repotting any plant that is in full growth or in bloom. Succulent plants do not require frequent repotting—only when necessary (when the roots become tightly packed) or once every two to three years. Large specimens can be repotted even less frequently. Succulent plants like to be slightly root-bound and so the new pot should be only one size up. Too large a pot is apt to retain too much water and lead to problems with rot.

Spiny plants will be easier to handle if you use kitchen tongs, a strip of newsprint or a piece of an old hose for small and medium-sized specimens or an old blanket or strap for larger specimens. Use clean, disinfected secateurs to remove any dead or unhealthy roots. The pot, preferably clay for large specimens, should have at least one drainage hole. Cover the hole, being careful not to block it, with clay pot shards or other coarse material, and fill the pot with slightly damp soil mix, placing the plant at the same depth as in the original pot. You should never water after repotting; allow the soil to dry out for two to three weeks before watering it. This will give any roots you have damaged a chance to heal. Avoid placing the plant in full sun for 3 to 4 weeks after repotting. Finally, you can top-dress the soil with 1 to 2 cm of fine gravel or coarse sand to improve drainage around the collar of the plant.

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