Rice water is one of the simplest DIY plant fertilizers you can make: rinse or soak uncooked rice, save the cloudy water, and use it to water your garden. The whole process takes 30 minutes for a basic batch or up to two days if you want to ferment it for extra nutrients. Here’s how to do it right, what’s actually in the water, and which plants benefit most.
The Soaking Method (Simplest)
Start with about half a cup of uncooked rice. Give it one quick rinse under the tap to remove any surface dirt, then place the rinsed rice in a bowl with roughly two cups of water. Let it sit for at least 30 minutes, swirling occasionally. The water will turn cloudy and milky as starch and nutrients leach out of the grains. Strain the rice out (cook it as usual) and the remaining liquid is your plant water.
This soaked version is ready to use immediately. Pour it directly into the soil around your plants the same way you’d water them normally. If you have leftover rice water, store it in the refrigerator and use it within a few days before it starts to smell off.
The Boiled Method
If you’re already cooking rice on the stove, you can collect that starchy cooking water instead. Boil your rice with more water than you normally would, then drain and save the excess liquid. Let it cool completely to room temperature before using it on plants, since hot water will damage roots.
Boiled rice water tends to be more concentrated in starch than the soaking method, so you may want to dilute it with an equal part of plain water before applying it to your soil. This is especially true for potted plants, where there’s less soil volume to absorb the extra starch.
The Fermented Method (Most Nutrient-Rich)
Fermenting rice water takes more time but delivers significantly higher nutrient levels. One study found that fermented rice water contained roughly 400 mg/L of nitrogen, 280 mg/L of phosphorus, and 1,000 mg/L of potassium. For comparison, plain washed rice water tested at about 160 mg/L of nitrogen, 91 mg/L of phosphorus, and 118 mg/L of potassium. Fermentation more than doubles most nutrient concentrations.
To make it:
- Soak half a cup of rinsed rice in two cups of water for 30 minutes, then strain.
- Pour the cloudy water into a clean glass jar and cover it loosely with a cloth or loosely fitted lid. Air needs to get in.
- Leave the jar at room temperature for 24 to 48 hours. You’ll know fermentation has started when the water develops a slightly sour smell.
- Move the jar to the refrigerator and use it within one week.
The fermentation process is driven by beneficial bacteria that break down the starch into forms that are more accessible to plants. If you see any black, brown, or orange growth on the surface of the water, discard the batch and start over. That discoloration signals unwanted mold or bacterial contamination.
What’s Actually in Rice Water
When you wash or soak rice, you’re pulling out the three nutrients plants need most: nitrogen (which fuels leaf growth), phosphorus (which supports root development and flowering), and potassium (which helps overall plant health and disease resistance). The water also contains smaller amounts of calcium, magnesium, and sulfur.
To put the nutrient levels in perspective, plain tap water contains almost no phosphorus (around 0.05 mg/L) and only trace potassium (about 6 mg/L). Even unfermented rice water delivers 15 to 20 times more potassium and over a thousand times more phosphorus than what comes out of your faucet. It’s a mild, organic fertilizer rather than a concentrated chemical one, which makes it harder to overdo but also means it won’t replace a balanced fertilizer for heavy-feeding plants.
Does Rice Variety Matter?
Brown rice retains its outer bran layer, which contains more fiber, minerals, and bioactive compounds than polished white rice. In theory, water from brown rice should leach out a broader range of nutrients. White rice has a higher starch content because the milling process strips away the bran, so its water tends to be cloudier and more starch-heavy. Either type works for plants. Jasmine, basmati, short-grain, or long-grain all produce usable rice water. The differences between varieties are small enough that you should simply use whatever rice you normally cook.
Which Plants Benefit Most
Leafy greens like lettuce, spinach, and bok choy respond well to rice water because the nitrogen encourages bigger, fuller leaf growth. Tomatoes and peppers are also good candidates, where the extra nutrients can promote more flowers and larger fruit. Citrus trees can benefit from the potassium and phosphorus boost, though you should avoid fertilizing citrus after early July, since late-season feeding makes them more vulnerable to frost damage and pests.
You can experiment with rice water on virtually any plant that tolerates liquid organic fertilizer. That said, be cautious with indoor plants. The starch in rice water can attract fungus gnats, ants, and surface mold in the enclosed, humid environment of a pot sitting indoors. If you do use it on houseplants, apply it sparingly and watch the soil surface for any signs of pest activity or fuzzy growth.
How Often to Apply It
Rice water is mild enough that it won’t burn roots the way synthetic fertilizers can, but that doesn’t mean more is better. Apply it no more than once a month to avoid mold buildup, pest problems, or shifts in soil chemistry. Between rice water applications, water your plants with plain water as usual.
For outdoor garden beds, pour the rice water directly at the base of the plant, soaking the root zone. Avoid spraying it on leaves, where the starch can leave a film and potentially encourage fungal growth. For potted plants, use just enough to moisten the soil without waterlogging it. If you’re using the fermented version, you can dilute it 1:1 with plain water since it’s more concentrated.
Think of rice water as a supplement, not a replacement for proper watering and soil care. It’s a free, low-effort way to recycle kitchen waste into a mild nutrient boost, especially useful for vegetable gardens and container plants that deplete their soil nutrients quickly over a growing season.