How and Why to Use Rice Hulls in the Garden

If you’re searching for the ultimate sustainable garden amendment, consider rice hulls, otherwise known as rice husks. This materially is essentially what’s left over once the food grain is processed. While you can compost this waste, its lignin content causes a slow decay. This is precisely what makes it so effective in garden beds.

This food byproduct is produced in abundance all over the world, and you can mix it right into the soil or use it as mulch. It improves water retention, drainage, and aeration. The lignin even protects it from pests. This method is valuable due its versatility, affordability, and gentle impact on the environment. 

In this piece, we’ll tell you what exactly rice hulls are, and we’ll explain how and why they’re beneficial. We will provide some basic instructions on how to apply this amendment, and we’ll even justify why you should opt for it over some others.

About Rice Hulls

Rice hulls are simply a byproduct of agriculture. They are the outer coatings of grains of rice, which means they are biodegradable and food-safe. 

After rice is soaked, steamed, and dried for culinary use, the husks are removed through the process of milling. Because people eat this grain all over the world as a true food staple, the byproduct is an available, copious resource that is otherwise considered waste.

In fact, estimates suggest that the worldwide production of rice includes 150 million tons of husks each year. That’s a huge opportunity for both farmers and backyard gardeners alike.

These husks have lots of lignin, which protects grains from pests while they’re growing. This is great news for gardeners. While some amendments may look attractive to pests, the lignin won’t interest them.

Better Soil Structure

These husks are excellent at improving soil structure. They are super lightweight and create small air pockets in the ground. This increases aeration overall and can improve the structure of compacted soil.

Plants’ roots need oxygen, and heavy, compacted dirt can suffocate them. Applying amendments that improve aeration, delivering precious O₂ to the roots, promotes the growth of roots and makes nutrient uptake easier.

Additionally, aerating increases drainage. Most plants grown for ornamental and edible purposes don’t like to sit in water for long. Mixing this amendment into your beds reduces the likelihood of rot.

Pockets of air in the ground are also necessary for a healthy soil microbiome. Worms, fungi, and all sorts of microorganisms are crucial for healthy plant growth. They break down organic matter and make nutrients available to plants, but they can’t do their job properly in poorly-aerated soil. 

Nutrient Content

To a degree, rice hulls themselves act as a slow-release fertilizer. They decompose in the soil with the help of microorganisms, adding available nutrients for plants.

Studies have found the nutrient breakdown to be about 2% nitrogen, 0.5% phosphorus, and 1% potassium. While this may be less than some standard NPK fertilizers, it’s a great baseline to have in your in-ground gardens and raised beds. Micronutrients are also found in this byproduct, including calcium, magnesium, iron, zinc, manganese, and copper.

This material is high in lignin, which causes its decomposition to occur a bit slowly. Because it happens over a wider range of time instead of all at once, you can rely on this additive to provide a light but consistent amount of nutrients over the course of a season, particularly nitrogen.

Leafy greens, fruiting plants like tomatoes and peppers, and root vegetables tend to use a lot of nitrogen, so having a long-term source of slowly-released nitrogen can be an asset, even when you fall behind on your fertilizing routine.

Moisture Retention and Balance

The ability to retain water in the ground could not be more important for gardening. Not only do most plants prefer to grow in moist but well-draining soil, but most gardeners prefer not to go outside and water their plants every day.

The inherent structure of these husks allows them to both absorb and retain lots of water. In times of excess precipitation, they can soak up all the extra water. In times of drought, there’s still water in the husks, slowly draining into the soil.

This consistent balance of moisture encourages plants to grow deep, sturdy roots. These roots provide nutrients and also make the plants themselves hardier. Even in times of extreme drought (or when you’ve left for vacation), plants with deep roots have more access to groundwater.

This ability to retain water allows for better nutrient balance and exchange as well. 

How to Apply Rice Hulls to Your Garden

In spring, around the time when you would normally freshen up your beds with compost, leaf mold, or something similar, you can apply rice hulls to your garden. Depending on where you live, you may be able to buy the product in bulk from a rice processing location for a low price.

Otherwise, you can purchase processed husks that are often optimized for gardening use at garden centers and similar retailers. They are usually treated in such a way that increases their durability and ability to retain moisture. This treatment also prevents germination of any remaining rice seed. Both raw and processed forms are effective. 

About two inches on top of the soil will get the job done. Mix it thoroughly into the top foot or so of dirt. You can also till this product into heavy clay to break it up a bit. Apply the amendment early in the season, so it has time to start breaking down before you start planting.

You can mix some into potting mix for potted plants and container arrangements as well. The amount to use depends on the quality of your current mix. Some suggest blending in up to 50 percent in your potting mix. You could also just add an inch or two on top of an old pot of soil and mix it all up with your hands.

Growers in temperate climates may want to amend their garden with rice hulls every year. If you live in an area that gets a lot of rainfall, which causes faster decomposition, you may want to apply it twice a year. Apply a second application in the same manner you would apply granular fertilizer.

How to Apply as Mulch

Rice hulls also make an effective garden mulch as an alternative to wood chips, bark, or straw. Apply about a 1-inch layer above the soil for mulch use. This will help prevent water loss from evaporation, minimize erosion, and suppress weeds.

When the soil doesn’t have a mulch layer, the sun’s rays cause a significant portion of moisture to evaporate. This causes your plants to get thirsty faster and forces gardeners to water more often. A simple application of mulch prevents this water loss, saving your plants from stress and saving you time and water.

Weeds need access to the sun to grow, and this amendment provides a surprisingly opaque layer. The blocked sunlight will prevent many weed seeds from germinating in the first place, and those that succeed will have a hard time getting to the surface.

Even if weeds manage to break through your mulch layer, the airy composition of the byproduct husks should make pulling them a breeze. Of course, weeds are more than just an aesthetic nuisance. They compete with your intended plants for nutrients, water, and space.

Versatile and Safe

Rice hulls work with a wide range of soils. This material has a neutral pH, so it won’t affect pH levels. If you’re intentionally cultivating acidic soil for blueberries, for example, the application of this amendment won’t knock you off course.

This amendment is also appropriate for all types of plants. Ornamentals, edibles, flowers, shrubs, and trees can all benefit from it in the soil and as a mulch layer. You can apply it to your vegetable beds without concern because it’s completely food-safe.

When mixing this amendment into your beds or using it as mulch, you won’t have to worry about introducing any dangerous bacteria. The same can’t be said for manure, for example, which can carry bacteria such as E. coli.

The airy nature of this amendment promotes solid air circulation, so it doesn’t encourage fungal disease, either. Plus, rich hulls contain silica, which is a natural pest-deterrent. Pests are frequently the spreaders of both fungal and bacterial diseases.

Sustainable and Gentle on the Earth

Rice hulls are a more sustainable amendment alternative to perlite, which is also used for aeration. Perlite is a non-renewable resource, but people all over the world eat rice every day. Not only is this grain byproduct renewable, but also there’s tons of it in production. If it’s not utilized, it will just go to waste.

Perlite, vermiculite, and other rock-based products also require mining, which disturbs habitat and ecosystems. When dealing with these products, one can also easily inhale their dust. Vermiculite may even contain trace amounts of asbestos.

The husk byproduct is also more environmentally friendly than peat, which increases moisture retention. The extraction of peat disturbs bogs, fens, and similar ecosystems. Additionally, these habitats sequester carbon from the atmosphere and harvesting peat releases that carbon, contributing to the rise of global temperatures.