Rice Watering Garden

 ‘Dear Kris,

I heard that after washing the rice water be used as a general fertilizer for plants and the garden? Do you think this is true or just an old wives tale?

Rasheenayen, Bali.

Well my mother-in-law swears by it, and as for myself I also water it around the garden. It seems to make sense and there is some scientific evidence out there to support the theory, unfortunately though there seems to be a lot more research into rice water for skin care, but if it can rejuvenate your skin and iron out the wrinkles then it must have something beneficial in the way of vitamins, minerals, amino acids or anti-oxidants I would assume – but I wouldn’t want to be the one make an ass out of you and me, so let’s take a closer look at the research.

Studies such as Malakar and Banarjee(1959) and those reviewed by Juliano (1985, 1993) have reported that washing rice on average causes up to half of the water-soluble vitamins and minerals to be lost from the rice. The exact amount of the nutrient loss would depend on the type of rice, how much water was used and the method of washing.

Generally, after a wash rice loses up to 7% protein, 30% crude fiber, 15% free amino acids, 25% calcium (Ca), 47% total phosphorus (P), 47% iron (Fe), 11% zinc (Zn), 41% potassium (K), 59% thiamine, 26% riboflavin, and 60% niacin. Logically it would follow that what was lost from the rice is now gained by the water. Following on it could be hypothesised that the leached nutrients now in the rice water could be beneficial to our houseplants.

A scientific study was carried out just a few years ago by graduate students under the supervision of Dr. Christopher Teh, (an expert in crop modelling, environmental biophysics, and soil conservation) senior lecturer from the Faculty of Agriculture, University Putra Malaysia.

The focus of the research studied the effect of rice water on kangkong otherwise known as water spinach – a vegetable most would be familiar with, especially those that like to eat padang, nasi campur etc.

The treatments were: 1) washed rice water, 2) NPK 15:15:15 fertilizer, and 3) control.

The rice water treatment meant that each kangkong plant was watered daily with 200 ml of water from washed rice, the NPK treatment was 5 g of NPK 15:15:15 applied on the soil once (before planting) per plant, and then watered daily with 200 ml of tap water. The control treatment plants were only watered daily with 200 ml of tap water per without any application of fertilizer or washed rice water. In the experiment the same white rice was always used, and the rice to water ratio was 1.0 : 1.5 L

The washing of rice was always done in the same way. The experiment continued for five weeks, at which point several plant growth parameters – leaf number, plant height, fresh and dry plant weight, leaf area, and specific leaf area or leaf thickness were measured.

Results of the study into the beneficial use of rice water for plants showed that using the water from washed rice is as effective, and in some cases more effective than NPK fertilizer in promoting plant growth, at least in terms of the number of plant leaves produced and higher plant biomass, and both treatments were more effective than the plain water control group. The implication from this study means washed rice water will produce better results than using plain water alone.

Other notable findings included higher potassium (K) and nitrogen (N) content in the plant (as well as in the soil for K). It could be deduced that rice water supplies the essential nutrients NPK needed by all plants and would have a favourable effect on any garden by accelerating growth and increasing biomass yield.

The physical results indicating faster growth and an increased bio-mass are directly attributable to the leached nutrients within the rice water. Further to this, information from other sources also indicates that the starches found in rice water accelerate growth of the many types of beneficial soil bacteria and fungi such as lactobacilli and mycorrhizae that can already be found to pre-exist in the soil – which then in turn feed the plants, helping plants grow stronger, healthier and more resistant to diseases.

Rice water is a mild fertiliser and consistent use could take the worry out of over fertilising. The starches from leftover rice water will help encourage beneficial soil bacteria, while the vitamins and minerals will add small amounts of NPK (nitrogen, phosphorus and potassium) to the soil. Obviously, you should wait until the water has cooled before you start to use it on the plants. In fact, using any sort of water left over after cooking or steaming vegetables, cooking pasta or boiling eggs would be beneficial for the garden as long as too much salt hasn’t been added. If you have a freshwater aquarium, water bowl or fish pond that too can be spread around the garden during water changes and cleaning. Fish poo is great for the garden, and the proof of the pudding is in the eating – the resulting fresh produce that is, not the fish poo itself!

Aquaponics has taken off to a commercial scale whereby fish that are bred for consumption have their pond water cycled through hydroponic garden beds growing fresh produce, usually within an industrial scale green house. Processing fish waste water in this way allows the pond water to be filtered and cleaned, with the plants withdrawing the beneficial compounds such as ammonia, which convert to nitrogen in the grow bed, which would otherwise build up to toxic levels to fish if left within the in the fish ponds. This is a brilliant example of both sustainability and synergy at work, healthy fish, healthy produce, with lower input of chemicals fertilisers and water purification chemicals – At the end of the process we have fish, fruit and vegetables!

I digress – aquaponics is a story for another day.

In its simplest form using rice water is a wonderful way to conserve water at the very least, but also a welcome addition as a fertiliser and soil conditioner that will help you get more out of your garden ornamentals and edibles. Simply pouring it out down the sink is more than just a waste of water, especially when your garden can use that nutrient infused water with NPK and other trace elements!

Dr. Kris

Garden Doctor Contact: gardendoctor@hotmail.com


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