Most gardening starts with soil care, and we’ve written before about how soil amendments are useful in improving or modifying the soil in our garden spaces. While we focused on more traditional soil amendments like compost, grass clippings, and other yard waste, recently we’ve learned that many gardeners are turning to another alternative: rice hulls. While this may sound usual to some of us, rice hulls are a useful soil amendment that turns an agricultural by-product into something useful. So, let’s dig in and learn about rice hulls for gardening!
What are Rice Hulls?
Rice hulls, also known as rice husks, are just what they sound like: the inedible outer layer of a grain of rice. Rice develops rice hulls to protect the grains during the growing season—remember, rice grains are the “seeds” of the rice plant. Made of tough, woody materials, rice hulls are a durable layer that are removed and discarded when the rice grains are processed for use as food.
Humanity eats a lot of rice every year, and that means producing and disposing of a vast quantity of rice hulls. So, over the centuries, various cultures and regions have developed uses for them. In both ancient and modern times, rich husks have been used to create cement for use as a strong yet relatively lightweight building material. Charred and powdered rice husk has been used as tooth powder for brushing teeth in parts of South Asia. Rice hulls have been used for insulation in home and as stuffing for pillow and cushions in many places. And, perhaps most deliciously, rice husks are sometimes used as an ingredient when making beer. These are all great ways to make use of what would otherwise be a waste product, and as it turns out there are more ways to utilize rice hulls in our gardens as a soil amendment.
Rice Hulls as Soil Amendment
There are several different uses for rice hulls/rice husks in the garden. Strong yet lightweight, durable yet absorptive, rice hulls can be mixed into any growing medium to lighten and loosen soil. They can also act as a biodegradable substitute for perlite or vermiculite, helping container soils regulate their moisture content while also preventing soil compaction. We recommend starting with the same soil/amendment ratios you’d use for vermiculite or perlite and adjusting as necessary. It’s important to remember that rice hulls will break down in the soil over time, and that’s a good thing. Worms love to eat them, and they add important mineral nutrients to your garden soil. Rice hulls are relatively inexpensive in many places and can be replaced as needed to refresh and condition soil in both containers and in-ground beds. Some sources we consulted indicated that rice hulls can raise the pH level of soil when mixed in, so please take that into account especially when using rice hulls in containers.
The rice hull product most often used for this are parboiled rice hulls (PBH) which are steamed to kill any seeds that may have been mixed in with them. We recommend using PBH products unless you’re willing to tolerate pulling some additional weeds here and there. And speaking of weeds . . .
Rice Hulls for Weed Suppression
We’ve never tried this ourselves, but while researching this article we did discover that some nurseries and container gardens use rice hulls for weed suppression. The process is pretty simple: by top-dressing the soil with rice hulls, we can prevent unwanted seeds from taking root and competing with our seedlings and saplings. The process is simple—just spread the rice hulls on the surface to a depth of between 0.5 and 1 inch/1.25-2.5cm and then water as normal. The barrier provided by rice hulls helps keep unwanted plants form taking root while also helping to retain moisture and providing protection from the sun and wind. As with rice hulls in the soil, top dressed rice hulls will break down eventually with all the benefits that can offer.
This has been an especially fun article to research and write. It captures everything we love about gardening: making full use of unexpected resources, thinking outside the box, and caring for plants and soil in creative ways. We’re still new to the use of rice hulls in the garden, so if you have any tips or tricks to share please let us know in the comments or via email. Gardzen is all about community and we love to hear from you!
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