Fermenting Rice Wash Water for the Garden
Turn Your Rice Rinse Water into Probiotic Garden Gold
If you're already washing your rice (and you should be!), don't pour that cloudy, starchy water down the drain. That milky liquid is packed with carbohydrates that beneficial bacteria absolutely love. With almost zero effort, you can transform it into a powerful probiotic boost for your garden, compost, and soil.
This technique comes from Korean Natural Farming and has been used by farmers for generations to cultivate beneficial lactobacillus bacteria—the same family of bacteria we use in fermentation. These good bacteria help break down organic matter, suppress harmful pathogens, and make nutrients more available to plants.
What's in Rice Wash Water?
That cloudy water isn't just starch—it's food for microbes. When you let it ferment naturally, lactobacillus bacteria (which are everywhere in the environment) move in and multiply rapidly. They love the starchy, slightly sweet environment and will dominate the fermentation, creating lactic acid that:
- Accelerates compost breakdown
- Suppresses harmful bacteria and fungi
- Improves soil structure
- Increases nutrient availability for plants
- Supports healthy root development
- Helps plants resist disease
- Washing rice sometimes feels like a waste of water - you could also just tip it straight into the compost - but not so much the garden - see below.
Think of it as bokashi for your garden, but even simpler.
What You'll Need
- Rice wash water (from washing any type of rice)
- A clean jar or container with a loose lid (I usually use a 5-20 litre tub)
- Patience (3-7 days)
- A warm spot in your kitchen
That's it. No starter culture, no special equipment.
How to Make It
1. Collect your rice wash water
The first rinse water is best—it's the cloudiest and starchiest. Save it in a clean jar. You can collect from multiple rice washing sessions until you have enough to work with (at least 1-2 cups).
2. Ferment at room temperature
- Leave the jar at room temperature (20-25°C is ideal) with the lid resting loosely on top (not sealed tight—you need some air exchange)
- Place it somewhere you'll remember to check it but where you won't knock it over
- Within 24-48 hours, you'll notice it starting to smell slightly sour and fermented
3. Watch for separation
After 3-7 days, the liquid will separate into layers:
- Clear or slightly yellow liquid on top - this is your lactobacillus-rich serum
- White sediment at the bottom - mostly starch and dead bacteria
The top liquid should smell pleasantly sour, like yogurt or sourdough. If it smells putrid or rotten, something went wrong—start again.
4. Harvest the serum
Carefully pour off or siphon the clear liquid from the top, leaving the white sediment behind. This is your finished lactobacillus serum.
5. Store or dilute
- For immediate use: Dilute 1:20 (1 part serum to 20 parts water) and use straight away
- For storage: Keep undiluted in the fridge for up to 3 months, or mix 1:1 with molasses or brown sugar to preserve it at room temperature indefinitely
How to Use It
For compost: Dilute 1:20 with water and spray over your compost pile when you turn it. This speeds up decomposition dramatically and helps suppress odors.
For soil: Water it into your garden beds diluted 1:20 once a month. It improves soil structure and feeds beneficial microbes.
As a foliar spray: Dilute 1:20 and spray directly on plant leaves early morning or late afternoon (never in hot sun). This can help prevent fungal diseases and give plants a probiotic boost.
For bokashi systems: If you're making bokashi, you can use this serum in place of expensive EM (Effective Microorganisms) solutions.
Troubleshooting
It smells rotten, not sour: The fermentation went wrong—harmful bacteria took over instead of lactobacillus. This usually happens if the jar was too dirty or the temperature was too warm. Discard and start again.
Nothing's happening after a week: Your environment might be too cold. Move it somewhere warmer (near a heater or on top of the fridge). Or try again in warmer weather.
The top layer is moldy: Some surface mold can happen. Just carefully remove it and use the clear liquid underneath. If there's extensive mold throughout, discard and start over.
It separated but smells like cheese: Perfect! That's exactly what you want. Lactobacillus creates that distinctive dairy-like, sour smell.
Level Up: Making Lactobacillus Serum with Milk
Once you've got your rice wash ferment going, you can take it further using a traditional Korean Natural Farming technique:
- Mix your rice wash serum 1:10 with fresh milk (any kind)
- Leave at room temperature for 5-7 days
- The lactobacillus will consume the lactose and the mixture will separate into curds (on top) and whey (below)
- Strain out the curds (maybe give to chickens/pets—they're basically a soft cheese)
- The remaining yellowish whey is an even more concentrated lactobacillus serum
This concentrated version can be diluted 1:100 for use and will keep longer.
The Fermentation Connection
If you're already making milk kefir, water kefir, or kombucha, you understand this principle—you're cultivating beneficial bacteria that out-compete the harmful ones. Rice wash water fermentation is the same idea, just applied to your garden instead of your gut.
The lactobacillus you're growing here is remarkably similar to what's in your kimchi, sauerkraut, and yogurt. You're just putting it to work in the soil instead of in your digestive system.
Why This Works
Lactobacillus bacteria are everywhere—in the air, on surfaces, on plant leaves. They're waiting for the right conditions to multiply. The starchy rice water provides perfect food, and the slightly acidic environment they create as they ferment discourages harmful bacteria.
In your compost and soil, these bacteria continue doing what they do best—breaking down organic matter and creating an environment where plants thrive. It's nature's own probiotic system.
Can I Just Pour Rice Wash Water Straight Into the Garden?
You can, but it's not ideal.
When you pour fresh, starchy rice wash water directly onto soil, the microbes that break down those carbohydrates need nitrogen to do their work. They'll temporarily pull nitrogen from your soil (this is called nitrogen immobilization), which means your plants can't access it during that time. It's the same principle as adding fresh wood chips or sawdust directly to garden beds—the decomposition process ties up nitrogen until it's complete.
What this means in practice:
- Occasional small amounts diluted with regular watering? Probably fine, especially in established gardens with healthy soil
- Regular concentrated applications poured straight on plant roots? Could stress your plants, particularly young seedlings or heavy feeders
- Into your compost heap? Much better—the compost microbes will use that starch as food
- Diluted onto lawns? Generally fine
Why fermentation makes all the difference:
When you ferment rice wash water first, you're doing that decomposition work outside the soil. The starch gets broken down by beneficial bacteria, and what you end up applying to your garden is:
- Nutrients already in plant-available form
- Millions of beneficial lactobacillus bacteria ready to work
- No nitrogen tie-up in your soil
- An actual boost to soil health rather than a temporary drain
Think of it this way: fresh rice water is raw ingredients, fermented rice water is a finished product. Both have value, but one does significantly more work for you.
The practical approach:
If you can't be bothered fermenting every batch (and realistically, who has time for that?), here are your options:
- Dilute heavily (1:10 with water) before applying to plants
- Tip it into your compost instead of directly onto garden beds—perfect use for it
- Water pathways or areas between plants rather than at the root zone
- Save it up until you have enough to make fermenting a batch worthwhile
- Pour it onto mulched areas where the decomposition can happen in the mulch layer rather than competing with plant roots
In Short: Fresh rice wash water won't kill your plants, but it's not doing them any favors either. Save it for fermenting when you can, or at minimum, dilute it well and pour it into your compost where those carbohydrates become food for beneficial microbes rather than creating competition for nitrogen.
Go Ahead and Try it!
Next time you wash your rice, save that cloudy water. Let it sit for a few days,(I keep mine out in the garden shed), harvest the clear liquid from the top, dilute it, and feed your garden. It costs nothing, takes almost no effort, and turns what would be waste into a powerful garden amendment.
Your plants will thank you, your compost will break down faster, and you'll have closed another loop in your kitchen ecosystem. That's the kind of resourcefulness that makes sense—both for your garden and for the planet.
If you haven't seen it yet - take a look at The Weedy Garden on You Tube - he has a lovely relaxed approach. I find it very comforting.
See also: Washing and Soaking Rice | Making Bokashi Bran | Introduction to Fermentation
