Rice Water for Plants: Does It Actually Work?
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Rice water is a very weak, homemade soil-microbe snack, not a fertilizer. One open-field trial found fermented rice water could match a full dose of mineral fertilizer on a leafy vegetable, but that was outdoor soil, and extension specialists say there is no research showing the same for houseplants in potting mix. For indoor pots the bigger issue is usually not what the water lacks but what it adds: starch, moisture and, if it sours, smell, mold and fungus gnats. If you try it, use it fresh, unsalted, rarely, and on one plant first.
| What you’ll read online | What the evidence shows | Verdict |
|---|---|---|
| “Packed with nitrogen, phosphorus and potassium” | A 2023 field-trial paper notes washed rice water holds far fewer N, P and K than an equal weight of NPK fertilizer. It also cites earlier averages of roughly 81 N, 65 P and 131 K mg/L, and in the paper’s own table only about a tenth of the nitrogen was in ammonium or nitrate form that roots can take up right away. | Weak |
| “Makes plants grow X% bigger” | Percentages quoted online have no source. The one controlled trial I found used 3-day fermented rice water on choy sum in outdoor soil: alone it was about equal to full-rate NPK, and half-rate NPK plus rice water did best. | True in that setup only |
| “Great for houseplants” | University of Maryland Extension: no research on home use, and the study it found used real soil, so results may not carry over to potting mix. A Costa Farms horticulturist says not to think of it as a fertilizer source. | Unproven |
| “Feeds good bacteria” | In the trial, soil that got fermented rice water had higher bacterial populations — and was more acidic than soil treated with NPK. Starch feeds all microbes, including the ones you don’t want. | Plausible, mixed |
| “Natural pest control” | I found no extension or peer-reviewed support. Indoors, starchy residue is more likely to attract flies and ants than repel pests. | No evidence |
Why the sources contradict each other
Southern Living says research shows rice water makes vegetables grow faster and bigger; Martha Stewart’s experts say it won’t replace a balanced fertilizer. Both are right, because they describe different situations.
- The positive result came from a Malaysian field trial on sandy clay soil: fermented rice water, applied every day at 5 mm, over three plantings of choy sum. That is a lot of water on a lot of soil, in a heavy-rain climate.
- The skeptical advice is about a houseplant in soilless mix, where a splash of rinse water carries very little nutrition and plenty of starch. UMD Extension adds that rice water’s nutrient content varies by rice variety, origin and how it’s made, so it won’t give a specific rate.
The sensible reading: rice water is a mild organic supplement for soil, best evidence with fermented water in real garden soil, and it is no substitute for a fertilizer with a known analysis. If you want to know what the numbers on a bag mean, see our guide to plant food vs fertilizer. One more note from the same trial: the fermented water was acidic (about pH 4.5), and the soil it was applied to turned more acidic than soil fed NPK alone. That matters if your plant dislikes low pH.
The real risk: rice water is also watering
Starch is food for microbes, and fungus gnat larvae live in the top inch or so of damp, organic-rich potting mix and feed on the fungi that grow there, according to extension guidance. Add starchy water to a pot that stays wet and you’ve built them a home. The most common problems are all moisture problems:
| What you see | Likely cause | What to do |
|---|---|---|
| Tiny flies hovering at the pot | Fungus gnats breeding in damp soil | Stop rice water, let the top 1-2 inches dry out, water from below, add traps (see below) |
| White fuzz or film on the soil | Mold feeding on starch and wet soil | Scrape off the top layer, increase airflow, skip watering until dry |
| Sour or rotten smell from the pot | Starch breaking down in soil that stays wet | Let it dry; repot into fresh mix if it persists |
| Yellowing or drooping, soil still wet | Overwatering or root rot, not hunger | Check roots; no fertilizer or rice water on a plant that’s already struggling |
If gnats do show up, yellow sticky traps confirm the problem, and extension guidance names Bti (a bacterium sold as a soil drench for fungus gnat larvae) as the targeted treatment. Neither fixes the cause, which is wet soil.
How to make it safely
| Type | How | Use within | Main risk |
|---|---|---|---|
| Rinse or soak water | Swirl uncooked, unsalted rice in clean water and pour off the cloudy water, or soak it 30-45 minutes and strain | Same day | Low nutrients; starch if overused |
| Fermented | Put rinse water in a clean jar about three-quarters full, cover loosely with a cloth, keep at room temperature out of sun for about 3 days (the length used in the field trial; blogs say up to 5) | Right after it turns faintly sour | Smell, bacteria, acidity — never use undiluted indoors |
| Cooking water | Water left from boiling plain rice, cooled | Same day | Skip it if you added salt, butter or oil |
- Always unsalted. Salt is harmful to plant roots, and it’s the one ingredient that turns a harmless rinse into a problem.
- Don’t save leftovers by accident. Fermenting in a covered jar is deliberate; a bowl of rice water left on the counter is not. Costa Farms’ Justin Hancock advises using it fresh and not storing it, because it can ferment and encourage bacterial growth.
- Throw out a batch that smells rotten rather than sour, or grows fuzzy or colored mold on the surface.
- Dilute fermented water. A 1 part to 10 parts water ratio is a common blog suggestion; UMD Extension declined to give a rate, so treat any ratio as a starting guess.
How often, and a fair way to test it
No extension service has set a rate. The guidance I trust most is also the most cautious: no more than once a month on houseplants. Blogs suggest every one to two weeks for outdoor vegetables, but that isn’t backed by research. Because the benefit is small, the only way to know whether it does anything for your plant is a simple comparison:
- Pick two similar plants in the same light, pot size and potting mix.
- Change only one thing. Water both on the same schedule with plain water; give one a single dose of fresh, unsalted rice water on a day when the soil is already dry on top.
- Label them and wait several weeks before judging. New leaf growth, color and soil surface are the signs worth checking.
- Stop at the first sign of gnats, mold or smell. That tells you more than any growth difference.
Where to try it, and where not to
| Plant or situation | Rice water? | Why |
|---|---|---|
| Leafy vegetables and tomatoes in garden soil | Best place to try | Matches the soil-based trial; Southern Living suggests ferment for 3 days for tomatoes |
| Houseplants (pothos, philodendron and similar) | Rarely | No research; moisture and starch are the risks. See our pothos watering guide for when the pot is actually dry |
| Succulents and cacti (jade, aloe) | Skip | They want soil that dries out; extra liquid and starch are the opposite of what helps |
| Orchids | Skip unless you have a reason | Mostly social-media advice with no extension backing; orchid roots dislike staying wet. Use an orchid fertilizer at label strength instead |
| Edible plants, repeated use | Occasionally | Rice can take up arsenic from soil; UMD notes this as a consideration, so don’t make it a weekly habit on food crops |
| Wilting, rot or pest-stressed plants | No | Experts advise against it on plants that are already struggling |
What to use when you want a real boost
If your plant is actually hungry — pale new growth, slow growth in active season — a labeled liquid houseplant fertilizer at the recommended strength gives a known dose. For outdoor beds, compost and worm castings feed soil life with a measurable benefit; see vermicompost and worm tea. If you’re curious about other kitchen liquids, we compared the evidence for banana water too.
FAQ
Is rice water good for orchids? It’s popular advice, but I couldn’t find an extension service or orchid society that recommends it. Orchid roots are easily harmed by constant wetness. An orchid fertilizer at the label rate is safer; see our orchid care guide for feeding schedules.
Can I use the water from cooking rice? Only if it’s plain: no salt, butter or oil. Let it cool fully. It carries more starch than rinse water, which is more reason to dilute it and use it sparingly.
Does a jade plant like rice water? There’s no evidence it does. Jade is a succulent that wants its soil to dry between waterings, so the water itself is more likely to hurt than help.
How do I know fermented rice water has gone bad? A faintly sour smell is expected. A rotten or putrid smell, or fuzzy or colored mold on top, means discard it. Don’t pour it on plants.
Is it safe on vegetables? Occasional use is low risk if it’s unsalted, but rice can take up arsenic from soil, as UMD Extension points out, so avoid making it a frequent routine on food crops, and wash produce as usual.
Sources: Nabayi et al. 2023, Heliyon — Combined benefits of fermented washed rice water and NPK mineral fertilizer on plant growth and soil fertility over three field planting cycles · University of Maryland Extension — Rice water fertilizer (Ask Extension) · Martha Stewart — Can You Use Rice Water to Fertilize Houseplants? · Southern Living — Plants that can benefit from rice water · University of Maryland Extension — Fungus gnats indoors
