Horn silica 501

What is horn silica (preparation 501)?

Horn silica, known in biodynamic practice as preparation 501, is the second of the two field spray preparations and the counterpart to horn manure 500. The starting material is finely ground quartz (rock crystal), which is packed into a cow horn and buried in the soil over summer. Before use, a very small amount is stirred in water for an hour, the dynamisation, and sprayed finely onto the plants in the morning.

Horn silica is the light preparation of the method. While horn manure works from below, on soil and roots, horn silica works from above: on the plant above ground, on light uptake, assimilation and ripening. It is credited with improving the quality, flavour, aroma and keeping quality of the harvest. The quantities are tiny: a few grams per hectare.

Horn silica and horn manure: the two poles

The two horn preparations form a deliberately designed pair of opposites and can only be understood together. Rudolf Steiner described it in an image: horn manure "pushes up from below", horn silica "draws from above", both attuned to each other, "neither too weak nor too strong". Horn manure belongs to the dark, moist sphere of the earth and is given to the soil in the evening; horn silica belongs to the bright, warm sphere and is sprayed onto the plant in the morning. The experienced practitioner Alex Podolinsky summed it up: horn manure gives the farm its "structure", horn silica makes it "sensitive" and attunes it to light and surroundings.

Where does the number 501 come from?

The numbering of the biodynamic preparations from 500 to 508 dates from 1928 and was originally a code name. It has become an international abbreviation. "501" stands for horn silica.

Origin and context

Horn silica also goes back to Rudolf Steiner and the Agriculture Course (GA 327) of 1924. Steiner introduced it as a necessary complement to horn manure. The idea: the soil alone cannot bring the plant to full ripeness and quality; that needs the forces of light and ripening that horn silica conveys. The practice of making and using it was later worked out by Wistinghausen, Masson, Stappung and by practitioners such as Maria Thun, Peter Proctor and Alex Podolinsky.

The idea behind quartz and horn

Quartz (silica, silicon dioxide) is a main component of the earth's crust and stands for the element of light in biodynamics. In nature, silica is found where light processes play a part, for example in the silicified structures of field horsetail or in the feather-light seed parachutes of the dandelion. Steiner connected silica with the ability to take in and pass on light. Ground finely, it forms a very large, light-active surface. This concept comes from Steiner's spiritual-scientific world view and is presented here as its original idea, not as a statement of physics.

Making horn silica

The making mirrors the polarity to horn manure: instead of manure in winter, quartz is transformed in summer.

Material and preparation

Use clear rock crystal or quartz, ground as fine as flour; the finer it is, the larger the light-active surface. The quartz flour is mixed with rainwater into a thin paste and filled into a cow horn. As soon as the mass has dried a little, the opening of the horn is sealed with moist soil.

Burying over summer

The filled horns go into the ground between Easter and Whitsun, in an open spot that gets sun all day, so that they are exposed to the forces of the summer sun. The pit is like the one for horn manure but should not be close to it. The quartz stays in the earth over summer; in autumn, from late September to early October, the horns are dug up.

Storage

Unlike horn manure, horn silica keeps very well and hardly loses its effect. After digging up, it stays in the horn or is tapped out and put into a glass jar. It is kept dry and in the light, exactly the opposite of horn manure and the compost preparations, which are stored moist and dark (see storing the preparations).

Effect on plants and ripening

In the biodynamic understanding, horn silica works through light: it promotes the plant's light uptake, its assimilation (the formation of sugars and building materials from light) and a harmonious ripening. A classic experiment by Erika Riese, Frieda Bessenich and Ehrenfried Pfeiffer (1941) supported this picture: horn silica cancelled the effect of a dye (eosin) that disturbs the plant's orientation to light, from which the researchers concluded that horn silica acts "like light" and promotes assimilation.

Early practitioners stressed an important point: horn silica promotes not only assimilation but the plant's whole metabolism (according to Georg Merckens). Karl Tress described increased assimilation, more dry matter and better ripening, as well as an "increase in flavour, aroma, keeping quality and sugar content" and more complete protein. It fits this picture that horn silica has been described as an antagonist of the ripening gas ethylene.

In biodynamic experience, horn manure and horn silica together "normalise" shooting and ripening: the plant grows more steadily and ripens more evenly than under mineral fertilisation. Ehrenfried Pfeiffer summed up the division of labour between the preparations: "Preparation 500 acts especially on the growth of the roots […], preparation 501 increases the capacity for assimilation."

Using horn silica

When applying it, the time of day, the growth stage and the quantity decide the effect, and here horn silica is more demanding than horn manure.

Time of day: morning

Horn silica is sprayed early in the morning, when the plant begins to take in light; many practitioners want to be finished before midday. Clear weather supports the effect; hot midday sun and drying or cold winds are avoided. The same applies under glass: spray in the morning and ventilate well. As ripening begins, the spraying tends to move to the afternoon.

Growth stage and rhythm

Unlike horn manure, which prepares the soil, horn silica is applied to the growing plant, typically from the second or third true leaf, or the four-leaf stage. Rhythmic sprayings have proved themselves: on three consecutive days at the same time, repeated every two to three weeks; Maria Thun worked with intervals of nine to ten days. For leaf crops the emphasis is before harvest, for fruit crops after flowering, for root crops when the root starts to thicken.

An important warning from practice: do not spray horn silica at the wrong time. On ripening plants it can trigger seed formation too early, and leafy vegetables can bolt. Anyone who neglects silica or sprays it too rarely risks, according to Hugh Lovel, that the plant's calcium metabolism also gets out of balance.

Quantity

The rate is very small: about one gram in 10 to 15 litres of water for 2,500 square metres, or about four grams per hectare; in orchards and soft-fruit plantings roughly twice that. In prolonged drought it has proved useful to spray horn manure in the evening and horn silica the next morning, the pair of opposites working together to balance growth and ripening.

Stirring

Like horn manure, horn silica is stirred rhythmically for an hour before application (vortex, chaos, opposite direction) and then sprayed promptly, because the effect of the stirred preparation fades after about a day. Clean the vessel between stirring horn manure and horn silica. More detail: dynamisation and applying the preparations.

Horn silica and Demeter

For Demeter farms horn silica is compulsory: the Demeter standards require it to be applied, in a way suited to the crop, at least once a year to the plants on all land. Together with horn manure, horn silica is one of the two compulsory sprays of biodynamic farming (more under Demeter certification).

Effect: what does science say?

As with all preparations, the isolated effect in high dilution is hard to prove and remains disputed. The eosin experiment of 1941 and later observations on assimilation and ripening are indications, not conclusive proof; they are reported here via the biodynamic literature. For the biodynamic system as a whole, the DOK long-term trial of FiBL (since 1978) shows advantages in soil fertility and humus. A sound argument names specific studies rather than making sweeping promises about quality.