Rice husk
Also known as Rice hulls, Rice husks, Parboiled rice hulls
In short
Rice husks are the hard outer coats of rice grains, a cheap by-product of rice milling. Parboiled rice hulls are used as a light gardening substrate and potting-mix additive that improves drainage.
How it looks
Small, pale tan to golden, boat-shaped husks a few millimetres long, stiff and light. Carbonised rice husk keeps the same shape but is black.
Signs
Hulls decay over time, though slowly, because of their high lignin content. A hull-rich mix drains freely and holds less water than some other aggregates.
What favours it
Hulls are made of hard materials, including opaline silica and lignin, which slow their decay.
Prevention
- Use parboiled hulls, the form sold as a gardening substrate.
- Blend hulls with peat, coir or bark rather than using them alone.
- Trial a new mix on a few plants before switching a whole collection.
Treatment
Start with the first step and move down only if the problem persists.
- If a hull-based mix dries out too fast, increase the share of coir or peat.
Pros and cons
Pros
- By-product of rice milling.
- Very light yet very effective at improving drainage, according to Texas A&M.
- Nitrogen depletion is less of a problem than with sawdust, according to Texas A&M.
Cons
- Decomposes over time, unlike perlite.
- Parboiled hulls retain less water than some other aggregates, so they are used for drainage rather than moisture.
Look-alikes
- Perlite
- Perlite is white, rounded and crumbly, not boat-shaped husks.
- Horticultural charcoal
- Charcoal is irregular black chunks, while charred husk keeps the husk shape.
Typical uses
Greenhouse bedding plants and general container mixes.
Related
Sources
- Rice hulls — Wikipedia
- Growing Media — Texas A&M AgriLife Extension, Ornamental Production
- Potting soil — Wikipedia
Written in our own words from these sources. Check a product label before using any treatment.