DARK HOLLOW FIELD GUIDE
BD501: Horn Silica Field & Garden Spray
BD501, or horn silica, is the biodynamic field preparation traditionally associated with light, leaf and fruit development, and the above-ground expression of the plant.
Quick start
- Use only a very small amount of horn silica, traditionally around a pea-sized portion for a field-scale batch.
- Stir into roughly 2.5 gallons of water for one hour, alternating vortex direction.
- Apply as a fine mist above the foliage, allowing it to settle over the plants.
- Apply in the morning while light is gentle, not under intense midday sun.
- Use the stirred preparation promptly.
What BD501 is
Horn silica is made from finely ground quartz placed in a cow horn and buried through the warmer part of the year. After it is lifted, the preparation is traditionally stored where it can receive light. Unlike BD500, which is used toward the soil, BD501 is used in extremely small quantities as an atmospheric spray over growing plants.
How to stir
Use warm rainwater when practical. Stir strongly around the perimeter until a deep vortex forms, then reverse direction, break the vortex into turbulence, and build a vortex the other way. Continue alternating for one hour.
How to apply
Horn silica is applied differently from horn manure. Use a clean sprayer capable of producing a fine mist and spray upward and over the crop canopy so the mist settles onto the leaves. A little goes a very long way.
Morning application matters. Choose a morning before the sun becomes intense, or a bright overcast period when rain is not imminent. Avoid spraying plants under strong midday sun.
Timing
Biodynamic growers often coordinate BD501 with the crop and the quality they are trying to encourage, sometimes using flower/air or fruit/fire indications in a biodynamic calendar. At Dark Hollow we regard these rhythms as useful indications within the practice, while also paying close attention to weather, plant condition, and season.
BD500 and BD501
The two preparations are complementary rather than interchangeable. BD500 is applied in coarse droplets toward the soil and is associated with rooting and soil processes. BD501 is applied in a fine mist over foliage and is associated with light and the plant’s above-ground development.