In time, bark- and peat-based composts (growing mediums) will break down, which is why regular repotting is important. A plant that suddenly loses much of its foliage, or shrivels, may have lost its roots, and this will become apparent when you knock the plant out of its pot and examine its condition.

These materials include Rockwool, which is produced for the horticultural industry from spun volcanic pumice. Rockwool looks like discoloured cotton wool, and the surface is sometimes stained green with an algae that grows in response to the nutrients.

On average, orchids need repotting about once every two years. Older established plants may be left for longer, especially when they do not outgrow their pots, while young plants need to be moved on every six months or so in order to maintain a steady rate of growth.

Once the compost has broken down in this way, the roots cannot thrive and will quickly die. Speedy repotting is essential. First cut away all the dead roots and remove all the old compost, then replace it with fresh material throughout. Roots that can be seen to circle the rim of the pot without penetrating to the bottom indicate that the compost (growing medium) is unsuitable.

The cause may be that the compost is too dense for the roots to penetrate, and once again repotting may be needed. Phalaenopsis are particularly reluctant to immerse their roots in a compost that they do not like, and will prefer to extend their roots over the rim of the pot into the air, where they will adhere to any surface with which they come into contact.

The advantages of these inorganic materials are that they are very light, easy to use, and, when the plants are repotted, the old mix can be left, causing less root disturbance.

You will also need a pair of secateurs or scissors and a sharp pruning knife, as well as a sterilizing agent and a few sheets of newspaper. There are two basic methods of potting. The first, “dropping on”, is done when young plants do not need any root pruning and when the compost (growing medium) is in good condition, and can be left intact. Because this causes no disturbance, dropping on can be done at almost any time of the year, but avoid the hottest and coldest months when the plants may be stressed or growing slowly.

Some orchid growers like to mix up their own special brand of orchid compost (growing medium) from locally available materials. These materials may include dried oak leaves and beech masts, mixed with live sphagnum moss. While these may be successful when made up by an experienced grower, beginners should seek advice from their local orchid nursery.