Fermented rice water is one of the simplest DIY fertilizers you can make: soak rice in water, let it sit for one to two days, strain it, and use it to water your plants. The fermentation process multiplies the nutrient content and introduces beneficial bacteria that support soil health. Here’s exactly how to do it, what’s in it, and which plants respond best.
What You Need
The ingredient list is short. You need half a cup of rice (white or brown both work), two cups of filtered or dechlorinated water, and a glass jar or container with a loose-fitting lid. Brown rice tends to have slightly higher levels of minerals like magnesium and sulfur, but white rice works well too. Avoid using water straight from the tap if it’s heavily chlorinated, since chlorine can inhibit the bacteria you’re trying to grow.
Step-by-Step Fermentation
Rinse your rice once or twice with plain water, then add it to your jar with two cups of filtered water. Swirl it around for 30 seconds to release starches and nutrients into the water. Cover the jar loosely with a cloth, coffee filter, or lid placed slightly ajar so gases can escape. Then set it somewhere at room temperature, out of direct sunlight.
Let the jar sit for 24 to 48 hours. During this window, naturally occurring bacteria begin breaking down the starches and sugars in the rice water, producing organic acids and multiplying nutrients. You’ll know fermentation is underway when small bubbles appear and the liquid develops a mildly sour, tangy smell. If it smells strongly rotten or musty rather than pleasantly sour, something went wrong and you should toss it and start over.
After 24 to 48 hours, strain out the rice (you can cook and eat it, or compost it). The cloudy liquid left behind is your fermented rice water. For a stronger brew, some growers ferment for up to six days. Research published in Pertanika Journal of Science & Technology found that longer fermentation (up to six days) produced higher concentrations of nitrogen, phosphorus, and sulfur. However, for most home gardeners, two days strikes a good balance between nutrient development and odor management.
How to Store It
Use your fermented rice water within a few days for best results. At room temperature, it stays usable for about 48 hours after you strain it. In the refrigerator, stored in a sealed glass jar, it lasts five to seven days. Making small batches (enough for two or three uses) is the easiest way to keep it fresh without waste. If the liquid turns an unusual color, develops a musty or truly foul smell, or grows visible mold on the surface, discard it.
What’s Actually in It
Fermented rice water contains a surprisingly broad range of plant nutrients. Analysis of white rice water shows nitrogen levels of 40 to 150 mg per liter, potassium at 51 to 200 mg per liter, and magnesium at 36 to 1,425 mg per liter. It also contains sulfur, calcium, and vitamin B1 (thiamine). These are modest concentrations compared to commercial fertilizer, which is why rice water works best as a gentle, regular supplement rather than a replacement for balanced feeding.
Fermentation amplifies the nutrient profile. One study found that rice water fermented with a bacterial culture reached 400 mg per liter of nitrogen, 280 mg per liter of phosphorus, and 1,000 mg per liter of potassium. You won’t hit those numbers with a simple home ferment, but the principle holds: letting the bacteria do their work concentrates the good stuff.
The pH of rice water starts around 5.5 and drops to roughly 4.25 by the end of fermentation, making it mildly acidic. This is gentle enough that it won’t dramatically shift your soil pH with occasional use, but it does give a slight acidic boost that certain plants appreciate.
The Role of Beneficial Bacteria
Fermentation doesn’t just change the chemistry of the water. It populates it with lactic acid bacteria, particularly species of Lactobacillus. These are the same types of microbes found in yogurt and sauerkraut. When you pour fermented rice water into your soil, you’re introducing these bacteria into the root zone.
Lactobacillus bacteria produce organic acids that can suppress harmful microorganisms in the soil. They also help break down organic matter into forms that plant roots absorb more easily, essentially making existing soil nutrients more available. Over time, regular applications can support a more active, diverse soil microbiome, which is a key factor in long-term plant health.
How to Apply It
Dilute your fermented rice water before using it. A 1:1 ratio with plain water is a safe starting point, though some gardeners use it at full strength for established plants. Pour it directly onto the soil around the base of your plants, just as you would with any liquid fertilizer. You can also use it as a foliar spray by putting diluted rice water in a spray bottle and misting the leaves, which allows plants to absorb some nutrients directly.
Apply it once every one to two weeks. Because the nutrient concentrations are low compared to synthetic fertilizer, there’s little risk of burning your plants, but overwatering with any liquid (rice water included) can cause root issues. Let the soil dry out between applications as you normally would.
Which Plants Respond Best
Leafy greens and fruiting vegetables show the strongest response. Studies on tomatoes, eggplant, and spinach found that rice water increased plant growth by 22 to 43% compared to plain tap water. Other research reported 9 to 26% growth improvements in mustard greens, lettuce, and oyster mushrooms.
Specific plants that do well with rice water include:
- Lettuce and spinach: the extra nutrients promote root development and larger, leafier growth
- Tomatoes: faster growth, more flowers, and larger fruit
- Peppers: increased fruit production
- Bok choy: bigger, leafier heads
- Citrus trees: improved flowering and fruit size
Acid-loving plants like blueberries, azaleas, and gardenias may particularly benefit from the mildly acidic pH. Succulents and cacti, on the other hand, prefer lean soil and infrequent watering, so fermented rice water isn’t ideal for them. Plants that are sensitive to overwatering or prefer alkaline soil are also poor candidates.
Tips for Better Results
A few small adjustments make a noticeable difference. First, use the water from your second or third rinse rather than the first. The first rinse often contains dust and debris, while subsequent rinses are cleaner and still nutrient-rich. Second, if the sour smell during fermentation bothers you, add a small amount of sugar (half a teaspoon per jar) to give the bacteria more food. This can speed up fermentation and produce a milder odor. Third, keep your fermentation jar in a warm spot. Temperatures between 68 and 80°F encourage faster bacterial growth.
If you’re cooking rice anyway, you can also save the cooking water and ferment that. Boiled rice water starts with higher starch content, which gives bacteria more material to work with. Just let it cool completely before starting the fermentation process.
Over multiple growing cycles, the benefits compound. A three-cycle study at the University of Putra Malaysia found that plants watered consistently with rice water produced 42% higher yields than those given only tap water by the third cycle. The soil bacterial populations also increased over time, suggesting the microbial benefits build with repeated use.