Plants from the Odontoglossum alliance are extremely reluctant to grow from the older pseudobulbs. It seems that any spare eyes that are not activated while they are young deteriorate rapidly, losing the ability to grow within a year or two. For this reason, odontoglossums are propagated differently from other sympodial orchids, but the method carries a greater risk to the plant and is not to be undertaken lightly.

Phalaenopsis occasionally produce keikis or adventitious growths from the old flowering stems. This is frequently seen with the species Phalaenopsis lueddemanniana and related species or hybrids. If you want to encourage new growth in this way, you can treat the flowering stems with keiki paste – a growth hormone enhancement that is available from some specialist nurseries or orchid sundry firms. First remove the small green bract that protects each node along the stem, then apply the paste.

If the treatment is successful, a new plantlet will grow, producing its own leaves and roots, which can be removed and potted up when large enough. Vandas orchids are monopodial orchids, but they are not so easy to propagate from.

Cattleyas are sympodial orchids that are also treated slightly differently. The creeping rhizome is much thicker than that of other orchids and is visible on the surface of the compost with the pseudobulbs spaced along it. Most cattleyas have two growing seasons in any year, producing new growth and roots in the autumn as well as in the spring. This makes it possible to start propagation during the autumn by severing the plant, which remains in its pot.

The plant that has become extremely lit with a length of bare stem at the base srd strong aerial roots along its length, be cut down by severing the rhizome at a point below the leaves and aerial roots. The leafless stump that is left in the pot will, in time, produce a new growth that can be grown on.

The majority of sympodial orchids with pseudobulbs can be propagated in this way, but there are exceptions, such as orchids from the Odontoglossum alliance. It is always worth potting up any spare back bulbs and growing them on to flowering, although this can take a few years.

When a back bulb does not grow, it may be too old, and any spare eyes are dead. An old back bulb that gets started into growth sometimes shrivels and dies before the new growth has got very far, and unless it has made its own roots, it is unlikely to survive.

Some genera will grow from back bulbs much more readily than others, and it can be a case of trial and error to find out which are most likely to grow for you in this way. If you find yourself with a handful of various back bulbs left over at repotting time, try placing them all in one seedling tray, then wait to see which start to grow. As new growths appear, take out the relevant back bulbs and pot them up on their own. Those that have not produced new growths within about three months are unlikely to grow and can be discarded.