Is there “gold in them thar hills,” or is it just silicon valley?

The field horsetail is a very unusual plant in more ways than one. Its most noticeable odd feature is its primitive appearance. In spring strange fawn and black striped stalks push up out of the ground to a height of about a foot, bearing at the top a brush-like cone dusted with cream speckles. These are the fertile stems of the plant. The stripes are in fact a series of joints which are encircled by toothed sheaths that shade from cream to black. These sheaths contain the spores. In the summer taller green foliage replaces these leafless spears, and it is these brush-like leaves, whose sole job is photosynthesis, that give the plant the name horsetail.

Many wild plants contain chemicals which have played an important part in folk history and medicine, but the field horsetail has a mineral constituent that marks it out from most other herbs. It is rich in silica as well as other minerals.

The silica gives it an abrasive quality that made it useful as a natural polishing agent. In the past the stems were harvested and dried and used to burnish pewter and to smoothe wooden surfaces in much the same way as sandpaper. Apparently in the days of the hurdy-gurdy, street players would treat the wheels of their instruments with dried horsetail to prevent the build up of resin. People even used it to polish and strengthen their finger nails!

This high silica content gives horsetail a role in biodynamic farming. Where plants have to grow in potentially wet conditions, damage from fungal attack can be a real problem. This risk can be significantly reduced by applying a silica preparation to the soil. 200gm of dried horsetail, suitably soaked and diluted is said to be sufficient to treat an acre of ground.

There are several species of horsetail, but the common field variety is the only one that isn’t toxic. Apparently the young shoots are eaten as a vegetable in parts of the Far East, and the plant has been more widely used medicinally. Because of its astringent and diuretic properties the dried herb was prescribed in the form of a gargle for throat infections and made into a form of tea to treat cystitis. Horsetail also includes anti-inflammatory agents, so adding an infusion to bathwater is still sometimes recommended to ease rheumatic pain.

Perhaps the most bizarre property of horsetails is their ability in certain circumstances to manufacture chemicals that they might not normally contain. If the conditions are right the plant will synthesise nicotine, though horsetail roll-ups are unlikely to catch on. They also have the unusual capacity to concentrate particular minerals from the soil in their tissues, and some species of horsetail will take up gold into their cells. You’ll never extract enough gold from dried horsetail to gleam – the amounts, if present, are minute – but at least you’ll be able to use it to buff up your fingernails and make them shine!