Horn silica 501: making it, applying it, timing for each crop

Horn silica, preparation 501, is the light preparation of biodynamics. It is used to promote ripening, flavour and keeping quality of the harvest, to bring order to growth and to make the leaves resistant to fungi. For Demeter farms it is mandatory, at least once a year on all crops.

It is sprayed early in the morning as a fine mist onto the green plants, usually two to three times a year. Four grams are enough for a hectare.

This article shows how to make, store and stir horn silica and when to spray it on fruit, vines, grassland, cereals and vegetables.

What horn silica is

Quartz, chemically silicon dioxide, is the main component of the Earth's crust. In its most beautiful form it is rock crystal: hard, clear, insoluble in water, and it lets light pass through unhindered. Christian von Wistinghausen describes how silica nevertheless finds its way into living beings, into grasses and horsetail, into the skin, eyes and nerves of animals and people. In the soil it forms the framework as grains of sand, in clay it is present as silicate, and in the finest distribution it floats in the air.

Ground very finely, quartz has a large, light-active surface. In this form it goes into the cow horn and into the soil, where it is exposed to the light and warmth of summer. Stirred in water for an hour and sprayed onto the plant, the preparation, according to Wistinghausen, conveys these light effects transformed in the soil. They promote and order the plant's metabolism.

Pierre Masson calls applying horn silica "spraying with light". Depending on the situation, it strengthens the plants or slows growth that is too lush. It gives them a crystal-clear quality of light, promotes upright growth and brings out the flavour and fragrance of the harvest. Under glass and in protected crops it compensates for lack of light and damps down the moist warmth in which fungi thrive.

The counterpart of horn manure

The two field spray preparations form a polarity and belong together in use. Steiner puts it this way in the Agriculture Course: horn manure pushes up from below, the other pulls from above, "neither too weakly nor too strongly".

The polarity runs through everything that happens with the two preparations:

Horn manure lays the foundation on which horn silica can work properly. According to Wistinghausen, only both together give the complete, harmonising effect. In practice this means: horn manure goes first, horn silica follows when the crop is green and growing.

Rudolf Steiner's recipe

In the fourth lecture of the 1924 Agriculture Course, Steiner gives the recipe following on from horn manure:

"Again you take cow horns, but now you fill them not with manure but with quartz or silica, or also orthoclase or feldspar, ground to a flour, and you make of it a mush about the consistency of a very thin dough, and fill the cow horn with it. Now, instead of letting the cow horn overwinter, you let it spend the summer in the earth, then take it out in late autumn after it has spent the summer there, and keep the contents until the following spring …"

Rudolf Steiner, Agriculture Course, 4th lecture (GA 327), translated from the German

That is still the basis today. Everything else is the experience of a hundred years of practice, gathered by Wistinghausen, Masson and Walter Stappung.

Making it

The starting material

Quartz with a silica content above 98 per cent is used: crystalline as rock crystal or quartzite, amorphous as agate or flint, plus the potassium feldspar orthoclase, which Steiner names explicitly. Most farms use rock crystal. Ehrenfried Pfeiffer recommended it in 1938; Pierre Masson collects it himself in the Alps and takes only pieces with a recognisable form and transparency. Clear, well-formed crystals, crystal offcuts from a lapidary or vein quartz are common. Sources are crystal hunters, mineral fairs and specialist shops.

You also need well-formed cow horns with several calving rings. Horn silica needs far fewer horns than horn manure, so it is worth choosing the finest. Wistinghausen uses each horn for horn silica only once. Horns that held horn manure are not used.

Grinding

The flour must be as fine as dust. Steiner himself was asked about this and answered: first in a mortar with an iron pestle "to a thin flouriness", and for quartz then further "on a glass surface". Little has changed. This is how the work goes:

1. Break it roughly. Large stones are broken up with a hammer on a steel plate until they fit into the mortar. A wooden frame around the plate catches the splinters.
2. Pound it. In the iron mortar the pieces are pounded to grit. A sawn-off steel cylinder has proved useful, for example an old oxygen or fire extinguisher cylinder, with a heavy round steel bar as pestle. Before first use, pound gravel or a glass bottle in it to loosen the rust.
3. Grind it. The grit is passed through a kitchen sieve into a mortar bowl and ground with the pestle, then rubbed to flour on a thick glass plate with a glass muller in circular movements. Little material at a time goes faster: a teaspoon is almost too much. If you have fine laboratory sieves, you can sieve in between and save part of the grinding. Ball mills with an agate jar and agate balls are also suitable.

Most people grind in winter, when there is little to do outside. Stappung likes best to work in the days between Christmas and Epiphany, the Josephine Porter Institute in the USA at Candlemas. In groups the grinding is often done together. Franz Dreidax suggested as early as 1930 doing it as a social task in winter, with reading aloud.

A dust mask is mandatory. Fine quartz dust penetrates into the alveoli of the lungs and can cause silicosis. So when breaking, pounding, sieving and grinding:

• wear a fine-dust mask of class FFP2 or FFP3,
• wear safety glasses and gloves against sharp splinters,
• open mortars and sieves only once the dust has settled,
• use closed sieve sets and shake only horizontally,
• grind wet on the glass plate, which binds the dust,
• stir nothing up when cleaning, or go outside to do it.

Filling

Shortly after Easter the flour is mixed with rainwater into a mush that just still flows. The horns stand upright, in a bottle crate or in sand, with the opening horizontal, and are filled to the brim. After 24 hours the silica flour has settled and some water stands on top. It is poured off and the horn topped up with mush. Once the mass has dried and is firm, the opening is sealed with moist earth.

Reckon on 150 to 200 grams of quartz flour per horn. Depending on the number of sprayings, that is enough for 10 to 20 hectares. Wistinghausen gives a simple calculation:

Hectares × sprayings × 5 = grams of horn silica Grams of quartz flour ÷ 150 = number of horns

A farm with 20 hectares and two sprayings therefore needs 200 grams, one to two fine horns.

Burying

The horns go into the earth between Easter and Whitsun, at the same time as the horn manure horns are dug up. The calendar that accompanied the Agriculture Course in 1924 gives the beginning of April. Peter Züblin buried them on Easter morning at sunrise.

The pit resembles the one for horn manure. It lies apart from it, at a spot the sun shines on all day. The horns are laid with the opening facing down or, if the flour is still moist, stood upright with the opening facing up so that nothing runs out. A tuft of sheep's wool on the opening separates the preparation from the earth without sealing it airtight. Maria Thun buried her silica horns only 20 centimetres deep. The same pit serves year after year.

Lifting

Steiner says: in late autumn. Wistinghausen digs them up at the end of September or beginning of October, Helga Wagner at Michaelmas. The older authors, Dreidax and Voegele, took the horn silica out in late autumn, and Maria Thun dug on a flower day in the first half of November. Both are proven practice. What matters is that the horns do not stay in the soil over winter.

The horns are carried upright, washed or scraped on the outside and dried. Once dry, the preparation comes out of the horn more easily. Knock it out or get it out with a knife and, for the tip, a bent wire. Freshly dug, horn silica often smells of humus-rich earth. Its colour depends on the rock: quartz flour stays white to grey, orthoclase gives a reddish brown.

Storage in the light

Horn silica is the only preparation that belongs in the light. Steiner found clear words for it: it does no harm to the horns that have spent the summer in the earth to lie "somewhere". "They may be shone on by the sun. That may even be good for them."

Today the preparation is stored either in the horn, hung up with the opening facing upwards, or knocked out into a transparent glass jar. The jar is not sealed airtight. A glass lid without a metal clip or a screw lid laid on loosely lets in some air. Masson puts it on a windowsill facing east or north-east, where it gets morning sun but no fierce midday sun, and shakes it from time to time. He makes sure there are no cables, routers or phones nearby. If there is no quiet place in the house, he puts the jar on a small platform on a post outside in the hedge.

Stored like this, horn silica keeps for several years. It is the only preparation that also keeps well in very small quantities.

Stirring

Horn silica is stirred for exactly one hour, like horn manure: vigorously form a vortex down to the bottom of the vessel, then change direction so that a seething chaos arises, then the next vortex. The whole technique is in the article Stirring the preparations.

Some rules from horn manure work apply more loosely here. According to Masson, water quality and temperature are less critical; lukewarm rainwater is still the best choice. Stirring takes place at dawn. Stirring at night, especially with machines, is unfavourable. If you stir horn manure and horn silica in the same barrel, clean it thoroughly in between.

Horsetail tea or liquid manure is often applied together with horn silica. Wistinghausen recommends this to support the silica processes in the plant.

Quantities

Wistinghausen's table gives half a cubic centimetre as the measure for one portion, at most one gram. With dense foliage, for example in orchards, Masson goes up to 50 to 100 litres per hectare so that all leaves are reached. On large areas the amount of water can be reduced considerably with suitable equipment.

Application

Time of day

Horn silica is sprayed early in the morning, ideally while the dew is still on. Masson is precise: right after sunrise, not before, if possible before eight o'clock. The air should be at most 22 degrees Celsius when spraying. Heavy dew, sunshine and no wind are favourable. On an overcast or slightly misty morning you may also spray if a long wet period with little light needs to be balanced. Avoid the heat of midday and days with drying or cold wind.

When ripening begins, the time of day changes. Then spraying is done in the afternoon to promote ripening. And there is evening spraying for special cases, see below under root vegetables and vines.

The preparation is applied immediately after stirring, at the latest three hours afterwards. A shower in the minutes after spraying does not reduce the effect. Do not spray in heavy rain.

Technique

Before filling, the preparation is filtered so that the fine nozzles stay clear. Horn silica is misted: with a blower or a knapsack sprayer under high pressure, at least two to three bar, up to twelve bar. The mist rises and then settles on the foliage. The aim is a fine veil that sunlight passes through. The leaves hardly get wet. The mist drifts in the slightest wind. So watch where it falls and walk the area accordingly. In the garden a hand sprayer with a fine nozzle is enough. When spraying, do not stand in your own mist.

How often

The Demeter standards require horn silica at least once a year on the plants of all areas, as suits the crop (chapter II.2.4). Practice usually goes further: two sprayings a year are the rule, three to four in the garden, more in viticulture in wet years.

For the leaves' resistance to fungi and insects, Wistinghausen recommends rhythmic spraying: on three consecutive days at the same time of day, that is at 24-hour intervals, repeated after two to three weeks. In his experience, repeated application increases yield, ripening, keeping quality and the balanced quality of the fruit. The Demeter standards explicitly name rhythmic spraying of horn silica as a biodynamic measure that comes before any permitted plant protection product.

With the same crop no more than three to four times a year and never twice within a few hours, Masson advises.

The lunar rhythm

If you work with the calendar, you place horn silica preferably in the ascending Moon and on the days that suit the crop: leaf days for leafy vegetables, fruit days for fruit, vines and fruiting vegetables, root days for the root crop before harvest. In fruit growing and viticulture, Masson describes the practice of spraying three times at intervals of about eight days when the Moon passes through the constellations of the fruit trigon. Which day is which today is shown in the planting calendar.

The right time for each crop

The basic rule: horn silica comes as soon as there is enough green leaf or fruit set shows, and it works most strongly in the period of most vigorous growth. Charlie Sievers puts it this way for every plant: ready when it has its first ring of leaves. A second time at fruit and seed formation.

Fruit growing

• First spraying before flowering, when the trees carry well-formed leaves, from the beginning to the middle of spring.
• Second spraying onto the still small fruits.
• At ripening once more, when the fruits are fully grown, now in the afternoon.
• After harvest, in autumn between harvest and leaf fall, in the afternoon, for ripening of the wood.

Do not spray into open blossom. Wistinghausen sums it up for fruit: after harvest and after flowering in the morning, for ripening of the fruit in the afternoon to evening.

Viticulture

• In spring one to three sprayings, as soon as five leaves have unfolded, and before flowering.
• In a rainy summer or with a tendency to fungal diseases, further sprayings from fruit set to the beginning of ripening.
• Three weeks to eight days before harvest, if it is not too hot and dry. Masson has seen wine quality improve markedly as a result and the grapes become more resistant to rot.
• After the harvest and before leaf fall in the evening, if the shoots are ripening poorly or the summer sprayings had to be skipped. This promotes ripening of the wood and the storage of reserves in the roots; budbreak next spring becomes more even.

Horn silica promotes upright growth and makes the shoots strong and supple at the same time. That makes tying in easier.

Meadows and pastures

After every cut and every grazing, horn manure and horn silica follow. Horn silica follows horn manure after eight to ten days, when the young shoots are about ten centimetres long. In spring it stimulates tillering on meadows and pastures. Masson observes in cattle farming that the animals are healthier when their feed has been treated with horn silica, and that the quantity and quality of milk and meat increase. In drought it is postponed, at the latest two weeks before the next use.

Cereals

• Winter cereals can already be sprayed in autumn, onto the well-developed young plants.
• In spring after tillering, from the two-leaf stage up to stem elongation.
• At stem elongation, then once more at ear formation.
• At grain formation, while the crop can still be driven through. Masson then sees a higher protein content in the grain.

In his cereal trials, Immanuel Voegele achieved the highest yield with horn silica during tillering.

Vegetables and garden

In the garden you go by the main crops and the successions. Georg Merckens made a yearly plan from this that has proved itself:

1. May to June: early vegetables such as lettuce, radish, cress, plus apples at the balloon stage of the blossom.
2. June to July: the middle successions such as kohlrabi, early cabbage, peas, carrots, cucumbers, tomatoes, beans, plus currants, walnut-sized apples and cherries.
3. July to August: late successions, winter and storage vegetables, strawberries after harvest, apples as colouring begins.
4. September to October: winter vegetables before harvest, strawberries, blackberries, ripening apples, now in the afternoon.

Plus the rules for individual crops:

• Lettuce and cabbage are sprayed when they begin to form heads. Freshly transplanted bare-root seedlings only get horn silica once they have taken and the leaves begin to curl in. Otherwise they bolt easily.
• Radishes only once bulb formation begins.
• Beans, peas, cucumbers, squashes not too early. Fruiting vegetables such as peppers, cucumbers, tomatoes, beans and peas respond particularly well to horn silica. Maria Lohrmann sprayed the warmth-loving crops three times a year: beans, cucumbers, tomatoes, maize, basil.
• Tomatoes, strawberries and cucurbits may also be sprayed in flower. They flower continuously and then set more flowers and fruit.
• Root vegetables such as carrots, beetroot and celeriac are sprayed in the evening two to three weeks before harvest. The force then passes from the leaves into the root, which becomes sweeter, more aromatic and keeps better. Matthias Thun sprays carrots and celeriac from 20 centimetres of leaf height. Maria Thun recommended sprayings every 14 days for root crops.
• Under glass horn silica is especially valuable because it compensates for lack of light. Young plants in pots or with root balls can be sprayed before planting out if they grow thin from lack of light or tend towards fungal attack.

When not to use horn silica

Horn silica is a strong preparation. It promotes transpiration and brings a lot of light into the plant. Clear rules follow from this:

• Not on plants standing still because of drought, heat or cold. The plant must be able to replace the water it transpires. Where you can water, water beforehand.
• In drought, horn manure goes first. Wistinghausen has found it effective to spray horn manure in the evening and horn silica the next morning to stimulate growth.
• Not on plants that are too young or too weak. Leave out areas with very young sowings or cover them.
• Not into open blossom of fruit trees, vines and most vegetables, except the continuous flowerers above.
• Not too late in the morning. In late-morning sun the mist can scorch the leaves. In great heat, spray just before sunrise.
• Not twice within a few hours.

And if it was too much after all? If a horn silica spraying at the wrong time has checked growth, spray horn manure in the usual amount onto the leaves. According to Masson, that releases the blockage.

Make it yourself or buy it

For your own batch you need a few fine rock crystals, an iron mortar, a thick glass plate, a good dust mask, two to three cow horns and a sunny spot for the pit. The grinding takes a few winter evenings. Burying and lifting are done in an hour. Because one horn is enough for many hectares, horn silica is the preparation with which starting to make your own is most worthwhile. Many preparation groups grind and fill together.

If you do not make it yourself, you can buy it ready-made. The Präparatekiste shop stocks horn silica as a single preparation, loose by the gram for larger farms, and in the field spray set together with horn manure and barrel compost.

Frequently asked questions

What is horn silica?

The field spray preparation 501: finely ground quartz or rock crystal that matures in a cow horn in the soil over summer. It is stirred in water and sprayed early in the morning as a fine mist onto the green plants.

What is horn silica used for?

Biodynamics uses it to strengthen the plant's connection to light, to order growth and to promote ripening, flavour, keeping quality and resilience. It is the opposite pole to horn manure, which works on the soil and the root.

What is horn silica made of?

Quartz with a silica content above 98 per cent, usually rock crystal. Steiner also names silica and the potassium feldspar orthoclase.

When is horn silica made?

The flour is ground in winter, filled into the horn and buried between Easter and Whitsun, and dug up again in autumn, between the end of September and the beginning of November.

How much horn silica do I need?

Four grams in 40 to 60 litres of water for one hectare; in the garden about a quarter of a gram in five to ten litres for up to 1,000 square metres.

When do I spray horn silica?

Early in the morning after sunrise, if possible before eight o'clock, at no more than 22 degrees, onto the green, growing crop. Once ripening begins, in the afternoon. Root vegetables two to three weeks before harvest in the evening.

Horn manure or horn silica first?

Horn manure first. Horn silica follows a few days to two weeks later, when the crop is green and growing. On grassland there are eight to ten days in between.

How long must horn silica be stirred?

One hour; after that it is applied immediately, at the latest after three hours.

How often a year?

At least once on all crops, as the Demeter standards require. Two sprayings are usual, three to four in the garden. For leaf health there is rhythmic spraying on three consecutive days.

May I spray horn silica in a drought?

Not on plants that suffer from drought or are standing still. Water first where possible. The sequence horn manure in the evening, horn silica the next morning has proved itself.

May I spray into the flowers?

Not on fruit trees, vines and most vegetables. Tomatoes, strawberries and cucurbits tolerate it.

How do I store horn silica?

In the horn or in a jar, not sealed airtight, in a light place with morning sun, away from cables and radio devices. Shake it from time to time. It keeps for several years this way.

Why do I need a mask when grinding?

Fine quartz dust reaches deep into the lungs and can cause silicosis. A mask of class FFP2 or FFP3 is mandatory when crushing.

Can I use horn manure horns for horn silica?

Steiner allowed it. Most makers nevertheless use separate new horns for horn silica, because used horn manure horns can hardly be cleaned inside without residue.

Sources

• Rudolf Steiner: Geisteswissenschaftliche Grundlagen zum Gedeihen der Landwirtschaft (Agriculture Course), GA 327, 4th lecture and answers to questions; quoted after Stappung, chapters 4.2 and 4.5.
• Christian von Wistinghausen, Wolfgang Scheibe, Eckard von Wistinghausen, Uli Johannes König: Anleitung zur Herstellung der biologisch-dynamischen Feldspritz- und Düngerpräparate, section "Hornkiesel-Präparat (501)", pp. 25–28, "Aufbereitung und Lagerung", pp. 73–74, "Bedarfsmengen", p. 76. English edition: Biodynamic Sprays and Compost Preparations: Production Methods.
• The same authors: Anwendung der biologisch-dynamischen Feldspritz- und Düngerpräparate, chapter 2 "Die Feldspritzpräparate", 2.2 "Hornkiesel", pp. 15–20, chapter 4 "Aufbewahrung", pp. 45–46.
• Pierre and Vincent Masson: Landwirtschaft, Garten- und Weinbau biodynamisch (2015), chapter "Hornkiesel (501)", pp. 35–42.
• Walter Stappung: Die Düngerpräparate Rudolf Steiners. Herstellung und Anwendung, chapter 4 (making horn silica) and chapter 14 (applying horn manure and horn silica), including Georg Merckens (1982), Maria Lohrmann (1932), Charlie Sievers (1986), Bernd Schimmele (1980), Immanuel Voegele (1930), Matthias Thun (2001), Maria Thun (1994, p. 116), Franz Dreidax (1930).
• Demeter e. V.: Richtlinien Erzeugung und Verarbeitung 2026, chapter II.2.4.