Rice Water for Plants: Does It Really Work as Fertilizer?

Rice water is widely promoted online as a free natural fertilizer for houseplants and gardens. The idea is plausible: washing rice releases small amounts of nutrients and organic compounds into the water that would otherwise be discarded.

Scientific research supports some potential benefits, but the evidence is much narrower than many social-media gardening claims suggest.

Studies have shown that washed rice water can contain nitrogen, phosphorus, potassium and other nutrients, and that repeated applications can influence plant growth, soil chemistry and microbial populations. However, nutrient concentrations vary substantially, and researchers have not established a universal application rate for home gardens or houseplants.

What is rice water?

Rice water is the cloudy liquid left after rinsing uncooked rice or, in some cases, after cooking rice.

Most agricultural studies focus specifically on washed rice water — the water produced when raw rice grains are rinsed before cooking.

This distinction matters because cooked rice water can contain much more starch and may behave differently from simple rinse water.

Does rice water contain plant nutrients?

Yes.

A 2021 study published in Agronomy chemically characterized washed rice water and found both macro- and micronutrients, including plant-available forms of nitrogen.

The researchers also found that the nutrient composition changed depending on how the rice was washed and how much water was used.

This variability is important. Unlike commercial fertilizer, rice water does not have a standardized nutrient analysis.

Can rice water actually improve plant growth?

Under some experimental conditions, yes.

A 2022 study tested both unfermented and three-day-fermented washed rice water on choy sum grown in sandy clay loam, clay and silt loam soils over three planting cycles.

The researchers found that rice-water applications affected plant growth, nutrient uptake, soil chemical properties and bacterial populations. However, the results differed by soil type and treatment.

This is an important limitation: a treatment that works in one soil does not necessarily perform the same way in a container filled with peat-based potting mix.

Fermented rice water may behave differently

Fermentation changes both the chemical and microbial characteristics of rice water.

Research has shown that rice water left to ferment can develop higher microbial populations and altered nutrient availability.

A three-day fermented rice-water treatment has therefore been used in several agricultural experiments.

This does not mean that longer fermentation is always better. Fermentation changes acidity and microbial communities, and there is no standardized home-garden recipe establishing an ideal fermentation period.

Rice water combined with NPK fertilizer showed strong results

A 2023 field study compared four treatments across three consecutive choy sum planting cycles:

• three-day-fermented washed rice water;
• a full recommended NPK fertilizer rate;
• half-rate NPK combined with fermented rice water;
• tap water as a control.

The combination of half-rate NPK and fermented rice water produced the strongest overall results for plant growth, nutrient uptake and soil nutrient levels.

This is especially interesting because it suggests that rice water may work better as a supplement to conventional fertilization than as a complete replacement.

Can rice water replace fertilizer?

Current evidence does not justify treating rice water as a complete replacement for a balanced fertilizer.

Its nutrient concentration is highly variable and depends on factors such as:

• rice variety;
• where the rice was grown;
• washing intensity;
• water volume;
• fermentation;
• storage time.

Commercial fertilizers provide known nutrient concentrations, while rice water does not.

For plants with a confirmed nutrient deficiency or high nutrient demand, a fertilizer with a declared N-P-K analysis is more predictable.

Does rice water contain a lot of nitrogen?

Rice water can contain nitrogen, including ammonium and nitrate forms, but describing it as a “high-nitrate fertilizer” is too simplistic.

The actual concentration varies substantially and may be much lower than the nitrogen concentration in a conventional fertilizer solution.

Without laboratory analysis, gardeners cannot know exactly how much nitrogen they are applying.

Does rice water change soil pH?

It can.

Repeated application of fermented rice water has been associated with changes in soil acidity in controlled experiments.

In the 2023 field study, soil receiving fermented rice water was more acidic than soil receiving conventional NPK fertilizer.

This does not mean every application of rice rinse water will dramatically change soil pH. The effect depends on the water, soil, fermentation and application frequency.

Can rice water improve soil bacteria?

Potentially.

Studies have found higher bacterial populations in soils receiving fermented rice water.

This is probably related to the organic compounds and nutrients available to microorganisms.

However, “more bacteria” does not automatically mean “better soil.” Soil microbial communities are complex, and beneficial effects depend on which organisms are present and how the system changes over time.

Is rice water good for houseplants?

This is where the evidence becomes much weaker.

University of Maryland Extension notes that there is little research specifically evaluating rice water for indoor plants.

Most published experiments have used actual soil rather than peat-, bark- or coconut-coir-based potting mixes.

Indoor containers also have limited drainage volumes, so repeated application of nutrient-rich or starchy liquids could behave differently than field irrigation.

For houseplants, a fertilizer with a known nutrient concentration remains more predictable.

Which plants benefit from rice water?

There is not enough research to create a scientifically reliable list of plants that specifically benefit from rice water.

Published studies have examined crops such as choy sum and other experimental plant systems, but the results should not automatically be extended to:

• orchids;
• succulents;
• tomatoes;
• roses;
• houseplants;
• fruit trees.

Claims that rice water is especially effective for a particular plant species should be treated cautiously unless supported by crop-specific research.

Is fermented rice water better than fresh rice water?

Research suggests that fermentation changes nutrient availability and microbial activity, but it is not yet possible to say that fermented rice water is universally better.

Three-day fermentation has performed well in some experiments, particularly when combined with conventional fertilizer.

At the same time, fermentation can lower pH and change microbial composition.

The best treatment may therefore depend on soil conditions and crop type.

Can rice water cause problems?

Yes.

Potential problems include:

• unpredictable nutrient concentrations;
• changes in soil acidity;
• excess organic material in poorly drained containers;
• unwanted odors from fermentation;
• microbial growth;
• nutrient leaching;
• possible contaminants associated with the rice itself.

What about arsenic in rice?

Rice can accumulate arsenic from soil and irrigation water more readily than many other crops.

University of Maryland Extension therefore raises an additional caution when considering rice water for edible plants: contaminant levels vary depending on where the rice was grown and how it was processed.

This does not mean ordinary rice water is automatically hazardous, but it adds another reason not to treat it as a standardized fertilizer.

Does starch in rice water help plants?

Starch itself is not a mineral nutrient that plant roots require in the same way as nitrogen, phosphorus or potassium.

Instead, starch and other organic compounds can serve as carbon sources for microorganisms.

This may influence microbial activity in soil, but excessive organic material in poorly aerated containers can also create undesirable conditions.

The common claim that plants directly “feed on the starch” in rice water is therefore misleading.

How should rice water be used?

Because there is no standardized home-garden application rate, the safest interpretation of current research is to treat rice water as an experimental supplemental input rather than a primary fertilizer.

If using it:

• use unsalted water;
• avoid water containing cooking oil or seasoning;
• do not replace a known fertilizer program where plants have high nutrient demand;
• monitor drainage and soil condition;
• avoid repeated heavy application in small indoor containers;
• stop use if odors, mold or root problems appear.

Is boiled rice water the same as rinse water?

No.

Most fertilizer research has focused on washed rice water produced before cooking.

Boiled rice water can contain considerably more starch and may have a different chemical composition.

Research findings for washed rice water therefore should not automatically be applied to thick cooking water.

Rice water vs. commercial fertilizer

What the research actually suggests

Rice water should not be dismissed as a gardening myth. Peer-reviewed studies show that it contains plant nutrients and can influence plant growth, soil fertility and bacterial populations.

But the opposite extreme — presenting rice water as a proven replacement for fertilizer — is also unsupported.

The strongest evidence currently suggests a more nuanced role: washed or fermented rice water may be useful as part of a broader nutrient-recycling strategy, particularly when combined with conventional fertilizer.

Frequently asked questions

Sources: Agronomy, Agronomy, Heliyon, University of Maryland Extension