Time and again people say that the secret to their healthy plants is just one thing: rice water—the water they use to wash rice before cooking. Similarly, others recycle the water used in washing beans or in cooking potatoes to water their plants.
Is rice water or potato water a good fertilizer for orchids?
Although rice water has some nutrients, epiphytic orchids do not grow in soil with microbes that can break down the nutrients. When it ferments and decomposes, it can create a bad smell, attract pests and fungal problems, accelerate the decomposition of the orchid medium, which can lead to root rot.
In this article, we will take an in-depth look into the benefits of rice water for plants, if those benefits also apply to growing orchids, and why some people claim to have success with it.
Let’s get started.
Benefits of rice water for plants
When we wash rice, a lot of starch is leeched into the water. This feeds the nitrogen-fixing bacteria in the soil around the roots (called the rhizosphere) and converts nitrogen into nitrates, a form that can be absorbed by the roots. This would help the plant to carry out photosynthesis and thus benefit plant growth.
Studies have also found that the water used in washing white rice contains a lot of nutrients of the rice, up to 7% protein, 30% crude fiber, 15% free amino acids, 25% calcium, 47% phosphorous, 47% iron, 11% zinc, 41% potassium, 59% thiamine, 25% riboflavoin, 60% niacin (Juliano, 1993). Some of them are important macronutrients for plant growth such as phosphorous, potassium, and micronutrients such as calcium and zinc.
Rice water does have benefits for plant growth. Syuhaibah (2017) performed a five-week experiment where specimens of water spinach were watered daily with rice water, NPK fertilizer, and tap water as control. The results show that using rice water as fertilizer produced more leaves and more fresh plant weight than using synthetic NPK fertilizer.
Problems of rice water to fertilize orchids
Despite the nutrients in rice water, it is not recommended for growing orchids, especially indoors. There are five major reasons:
1. Epiphytic orchids don’t grow in soil with microbes to break down nutrients
Epiphytic orchids do not grow in soil and thus do not have enough microbes, if any, around the root area to break down the large molecules of nutrients such as proteins, carbohydrates into forms such as nitrates (NO3) that can be absorbed by the plant.
Even though there are microbes around the root area, the release of nutrients from the rice substances is slow, ranging from a couple of weeks to months depending on the temperature, pH of the environment. This would not work with orchids that need to be flushed every 1-2 weeks to remove salt build-up. Nutrients and microbes would be removed in each flushing.
Also, epiphytic orchids generally need to be repotted with a new moss and bark medium every 1-2 years. Whatever colony of microbes in the medium has to be replaced, making it impossible for the larger molecules of nutrients to break down for absorption. Therefore, what works with plants grown in the soil does not necessarily work with epiphytic orchids.
2. Rice water can attract pests and diseases
While rice water contains much starch which can promote soil biota beneficial for the nitrogen-fixing bacteria around the roots, it can also attract pests such as spiders and ants who may also be feeding on the starch.
Also, some rice may come with small insect eggs. So, washing rice with water and using it to water your orchids could introduce insects to your orchid medium.
3. Rice water accelerates the decomposition of orchid medium
Rice water ferments quickly after a couple of days depending on the temperature. The fermentation of rice water will introduce a sour and even stinky smell to the orchid medium.
Not only is the smell unpleasant for house plants, it also accelerates the decomposition of a medium of bark or moss. A decomposed medium is often compacted and stays moist for too much time for orchid roots, making them easy to have fungal and root rot problems.
4. Rice water does not have sufficient and complete nutrients
Rice water cannot replace fertilizers completely because it does not contain all the nutrients and in a sufficient quantity required by plants.
Also, it’s hard to control the quantity of nutrients existing in rice water because it varies by the type of rice. For example, the water from brown rice, organic rice does not contain many nutrients compared to white rice water as they are not milled much.
It also depends on how many times and how rigorous the rice has been rinsed. Too much nitrogen can make the plants grow very well but would stop blooming.
5. Preparing rice water is not worth it
Preparing rice water is quite an effort. It seems easy but it needs to be used immediately after rinsing rice or stored in a place for a week maximum before use. It takes preparation time and storage space. Plus, the quantity would probably be enough to water just one or two orchids.
If rice is not your staple food and you do not eat rice every day, you would be wasting food to just make some rice water.
On the other hand, synthetic orchid fertilizers are very affordable and offer a complete profile of nutrients required by orchids. For example, a bottle of “Orchid Focus Growth” with complete macronutrients and micronutrients costs only US$14.46 and can last two years for most home growers, because it needs to be diluted into a very weak fertilizer. Plants cannot tell the difference between nitrates from organic substances or from synthetic fertilizers.
So, why bother?
Why do some have success with rice water on orchids?
There are always many anecdotes around. This not only happens to using rice water, but also coffee, milk, etc., in watering orchids.
But, anecdotal evidence is fraught with human bias and the lack of controlling external factors makes it impossible to conclude that the organic fertilizer applied is the direct cause of plant growth.
Ultimately, scientific experiments need to be carried out to test out the use of rice water on orchids. Since there have not been any research on this topic, I can only offer my doubts.
To sum up, rice water, potato water, or water from washing beans, etc. contain some nutrients beneficial for plant growth.
However, the benefits do not apply to orchids and it can even do harm to your orchids. The problems include pests, fungal problems and medium decomposition, leading to a higher chance of roots rot. It is not worth it to risk your orchids.
Considering that orchids are mostly grown indoors, a complete synthetic NPK fertilizer would be a safer and cost-effective choice.
Juliano, B. O. (1993). Rice in human nutrition. Rome: International Rice Research Institute Food and Agriculture Organization of the United Nations.
Syuhaibah S. A. (2017). Use of washed rice water as a fertilizer. (Unpublished Bachelor’s final year report). Universiti Putra Malaysia, Serdang. published on http://www.christopherteh.com/blog/2017/11/washed-rice-water/