Frequent repotting of house plants is unnecessary, and generally plants placed in containers 5 inches or larger in diameter can stay in the same pots for 12 to 18 months. Most kinds will thrive in pots that appear too small for them, and many that have filled their pots with roots will grow satisfactorily if fertilized regularly. Late spring or early summer is the right time for repotting, because the roots then have time to become established before winter.

Top-heavy growth is often the main reason for repotting, but before repotting, inspect the ball of soil. If the roots are obviously overcrowded cr tangled around the outside of the soil ball, transferring to a pot one size larger is necessary. Cover the drainage hole of the larger pot with crocks, stand the soil ball in the centre, then fill up with potting soil and firm down. If repotting is unnecessary, drop the ball back into the same pot and tap the base sharply once or twice. The plant should then be firmly in place, but if it is not, firm the soil with both thumbs.

A good potting compost, suitable for most house plants, contains: 2 parts turfy loam, (loam containing undecayed grass roots), 1.5 parts leaf-mould or peat moss, 1 part washed coarse sand, part dried manure (all parts by volume).

The reaction should be slightly acid with a pH of 5.5 to 6 . Add bone meal at the rate of 1 pint to each bushel of soil mixture. For plants
that need soil especially rich in organic matter, such as African violets, begonias and gloxinias, double the proportion of leaf-mould or peat moss. Plants of the pineapple family (bromeliads) thrive best in a loose, porous mixture that contains a large proportion of pieces of orchid fibre (osmunda), rough, half-decayed leaves and lumps of charcoal, mixed into some turfy soil.

At potting time the soil mixture and the ball of the plant should be just moist. After repotting, water sparingly for a few weeks to encourage the roots to grow into the new soil.