Gardening: Keen to be clean as well as green? Here's how to grow your own soap

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Take a tip from North American Indians, writes Helen Lewis, and lather up with a yucca plant.

There is more to garden plants than meets the eye. Take the North American yucca, for instance, grown in this country for its sword-shaped leaves and showy flowers. North American Indians once ate the flowers, fruits and seeds, fermented the sap into a potent alcoholic drink, wove leaf fibres into ropes and cloth and washed themselves in soap obtained by boiling the root.

Along with many other plants, the yucca contains high levels of the substance, saponin. Although harmful if consumed in large quantities, plant saponins have some intriguing properties: the ability to form a lather in water and to be a gentle but effective cleanser. Saponin has other qualities, too; it can be an effective treatment for mild skin complaints.

The cleaning properties remove dirt but not oil, so, although useless for washing hands after tinkering under the car bonnet, they will remove soil from hands after weeding the garden and do so without stripping the skin of its natural oils. The soap makes an exceptional hair wash, and is included in many shampoos sold today.

In the commercial world, soap is manufactured using wood or plant ashes mixed with an alkali. Oils - usually palm oil - are added, along with herb extracts or essential oils to give a pleasant aroma. Obtaining home- grown "soap"is much easier. Simply add a quantity of chopped plant to boiling water, simmer for five to 10 minutes, then leave to infuse for an hour or more. The resulting liquid can be used for cleaning either clothes or the body.

The various ceanothus shrubs contain an abundance of saponin and thrive in sheltered, sunny positions in the garden. All ceanothus will tolerate some lime - but not shallow chalk - and produce vivid blue, pink or white flowers in profusion throughout the summer. When you need a wash, just pluck a handful of flowers, wet them and rub them over the body. They form a rich, gentle lather with a pleasant perfume.

Chlorogalum pomeridianum, the soap lily, is a bulbous plant from California that is grown in Britain more for botanical interest than for floral display. However, it is quite happy in warmer districts of this country if given a rich, well drained soil and a sunny position. The bulb, if dried and with its outer skin removed, can be grated and used as soap flakes for washing clothes.

Philadelphus coronarius, or mock orange, is a popular shrub bearing white, intensely fragrant flowers during the summer. The flowers are full of saponin and leave a wonderful aroma if wetted and rubbed on the body. The leaves and bark can be used, too, if first boiled and infused.

If you don't want to grow your own soap, there are plenty of wild plants around - the most obvious being our native Saponaria officinalis, or soapwort. This perennial can be found colonising damp ground, especially around hedgerows, woods and streams. It is invasive and will rapidly smother other plants, so if you want some for the garden, keep it in a pot. Boiled roots of the soapwort are still used today for cleaning delicate fabrics, including the Bayeaux tapestry.

Other plants with high levels of saponin include bracken and ivy. Lastly, the fruit of Aesculus hippocastanum, the horse chestnut tree, contains an abundance of saponin. Conkers will readily lather in soft water if rubbed between the hands like a bar of soap - but beware, their distinctive aroma leaves much to be desired.

For further information, Plants For A Future provide details of many alternative plant uses, and the plants themselves are available by mail order. For details contact The Field, Penpol, Lostwithiel, Cornwall, PL22 ONG. (01208 873 554).