There are several ways to increase numbers of bulbs without growing from seed. In the second of two articles on propagating bulbous plants, David Hide and Alan Toogood adapt some vegetative methods used by nature itself

To make the most impact in a garden, bulbous plants are often required in large numbers. If 'left to nature' they can increase by themselves but means of propagation that manipulate those natural principles can prove to be quicker and more effective. Gardeners need to find alternatives to growing plants from seed because it is such a slow method, and only species (as opposed to cultivars) will generally come true to type. Last month we looked at propagating by division, bulbils and bulblets, but there are many other useful and inexpensive ways to bulk up bulb stocks.

Which method?
The propagation techniques of scaling, twin scaling, scooping and scoring, and chipping - although slower than division, bulbils or bulblets, and only applicable to bulbs - are ideal when large numbers are required. They are also quick, easy methods for those bulbs that do not produce many offsets. Each scale or segment of a bulb may produce more than one new bulb.

Sectioning is an easy and quick technique for propagating certain stem tubers; this is particularly useful where only a few new plants are needed. For larger quantities, some bulbs and stem tubers can be propagated from leaf cuttings. This can be fairly challenging and slow, although it is the standard method for Sinningia (including gloxinias).

Keeping clean and tidy
It is important only to use disease-free material - either newly bought or freshly dug from the garden. Hygienic, controlled conditions under cover are needed and knives must be regularly cleaned with methylated spirit - even to the point of setting light to the blade.

Bulbs, corms and tubers are prone to rotting, so where fungicidal treatment is recommended during propagation to help prevent rot, particularly to treat wounds and cut surfaces, coat with sulphur dust (Vitax Green Sulphur or Vitax Yellow Sulphur).

Underground storage organs
A bulb consists of a basal plate - a compressed stem. Roots grow from this, together with a flower bud enclosed by fleshy, modified leaves known as scales.

Tunicate or ‘non-scaly' bulbs
Although all bulbs have scales, some species such as Narcissus, Allium and Tulipa have tightly-packed scales and their bulbs appear smooth until cut open. They are known as 'non-scaly' or 'tunicate' bulbs because the bulb is enclosed in a papery, protective tunic.

Scaly bulbs
Other bulbs such asFritillaria and Lilium have loose, easily separated scales without a protective tunic. These 'scaly' bulbs are more prone than tunicate bulbs to physical damage and drying out when out of the ground.

Descriptions and diagrams of different types of bulbs, corms and tubers appeared in the first article. See Basic Propagation Techniques

Hygiene
With all these bulb propagation techniques, scrupulous hygiene is essential to prevent disease from entering the cut segments. Wear surgical gloves or wash your hands very carefully, and use a sterile cutting board. The knife or scalpel should be wiped with surgical or methylated spirit, or held in a flame, between each cut.

Propagation Techniques

A selection of suitable bulbous plants to increase by these techniques

David Hide is Senior Supervisor of propagation within the Glasshouse Department at RHS Garden Wisley

Alan Toogood is Features Co-ordinator for The Garden and editor-in-chief of the new RHS Propagating Plants, published by Dorling Kindersley. Pages 253-79 are about propagating bulbous plants. The book is available from bookshops and by post for £25 plus £4.50 p&p (UK) from: RHS Enterprises Ltd, RHS Garden Wisley, Woking, Surrey GU23 6QB.
Mail order enquiries, tel: (01483) 211320. or buy online at http://www.gardeningstore.com or Dorling Kindersley online