Most of us gardeners know by now that we should trade peat moss for more sustainable choices (like coconut coir), because of the negative consequences of harvesting the stuff on the plants and wildlife native to the peatlands—not to mention, depleting our planet’s peatlands, which store three times as much carbon as forests, would worsen global warming. But did you know that we should also consider replacing perlite, the little, white, styrofoam-looking balls often mixed into store-bought soil to provide aeration and drainage? While perlite is quite useful and effective, there is actually a more sustainable and environmentally friendly option now: rice hulls.
What are rice hulls?
Rice hulls are the thin papery casings on rice, similar to corn husks, that act as a protective covering. The process is that after the rice is harvested, millers remove the hulls and then parboil them at a high heat to kill any weed seeds, bacteria, and diseases. In the past, hulls were discarded but luckily we’ve learned that they can be repurposed.
Why are rice hulls better than perlite?
From an environmental standpoint, rice hulls are the best choice. For starters, they are a renewable resource as they are a byproduct of agriculture (like coconut coir) that would otherwise be tossed. Plus, rice will most likely always be grown so there will always be rice hulls. Perlite, on the other hand, is non-renewable. To make it, obsidian rock is mined with large equipment, then crushed, and heated to extremely high temperatures—an environmentally harmful process. Last, rice hulls are more affordable than perlite and safer to handle and work with.
“We replaced peat with coco coir about 15 years ago, moving from an unsustainable to sustainable component, and more recently replaced perlite to rice hulls,” shares Jim Salyards, Filoli‘s Director of Agriculture. “Like perlite, rice hulls have the same balance of porosity and moisture retention, but are just a byproduct of rice farming.”
What benefit do rice hulls provide?
Rice hulls can improve soil texture, increase water holing capacity, and allow for better drainage by loosening compacted soil. The other advantage is that rice hulls are biodegradable so they feed the soil as they breakdown. For example, rice hulls add silica, which strengthens plant cell walls and improves the plant’s ability to ward off diseases and handle heat and drought. Lastly, when spread out like mulch and mixed into the top 1/2 to 1 inch of soil, rice hulls can help retain moisture and ward off weeds.
Rice hulls will decompose after about 2 years so your soil might sink, but the solution is to just add more rice hulls. Another issue is availability. Perlite is way easier to source, but luckily more gardeners are making the switch, which means more retailers will start carrying rice hulls and rice hull-based soil mixes.
The green takeaway
With sustainability being increasingly important these days, it is always a good idea to make choices based on what is beneficial to you and your garden and what helps protect and preserve the planet’s resources.
For more environmentally friendly gardening ideas, see: