Using rice water as an orchid fertilizer has been one of those organic, do-it-yourself tips that have been passed down through generations. Except whenever someone asks what is in the rice water, or how it helps orchids grow, nobody has a specific answer. So, I set out to find it, and just like the garlic water article (LINK), I was pleasantly surprised with the results.
Rice water is favorable for orchids because 1) it increases the starches that beneficial fungi use; 2) it provides the orchid with protein, crude fiber, free amino acids, calcium, phosphorus, iron, zinc, potassium, thiamine, riboflavin, and niacin in tiny doses; 3) and rice water promotes accelerated growth, healthy orchid leaves, and stronger, larger orchid roots.
Image Credit: © 2021 Orchideria. All Rights Reserved.
Is Rice Water Scientifically Researched or Is It An Old Wife’s Tale?
To find the answer above about rice water, I had to wade through tons of articles. Some had totally contradicting points, but it was all I say, you say… The research just wasn’t there. It’s easy to be accustomed to what we hear and with out scientific study, the old wife’s tales might (or might not) be true.
The hardest part was to get the information that had scientific research already published and apply that specifically to orchid care, where there isn’t that much that is available and accessible to the public.
Orchid roots are a whole different ballgame, since 75% of orchids are epiphytes or lithophytes, attaching themselves to trees and rocks. Only 25% of orchids are terrestrial or semi-terrestrial. That means the way the roots work is fundamentally different in each case, singling them out from the rest of houseplants.
If you have a semi-terrestrial or terrestrial orchid, then a lot of this information will not apply to you in the same way. That is good news, because you can readily take the research that is applicable to other household plants that thrive in soil, and the results will be the same.
In this article though, I will be addressing strictly the epiphytic orchids such as Phalaenopsis, Cattleya, Dendrobium, Catasetum, Oncidium, and others and how rice water affect their roots and leaves.
The good news is that what our grandmothers told us about using rice water is now proven in orchid care and research has finally proven what they had known all along. Let’s get into point by point of how rice water is good for fertilizing orchids naturally.
The NPK of Rice Water and How it Affects Orchids
The translucent water will contain mainly crushed particles of rice but can also contain other minerals that have been added to the rice plantation. Half of the water-soluble minerals will be transferred from the rice into the water.
One article, Rice Watering Garden, cited a study performed by Malakar and Banarjee (1959) reported that after rinsing the rice, the nutrients it transferred to the water were roughly:
30% crude fiber,
15% free amino acids,
25% calcium (Ca),
47% phosphorus (P),
47% iron (Fe),
11% zinc (Zn),
41% potassium (K),
26% riboflavin, and
Please note these are percentages compared to the rice’s natural uncooked grain, not the total percentage in the water. That’s why it doesn’t add up to 100%.
I didn’t find the NPK of rice water, just the boiled water, and I don’t use that. The authors justified the lack of an exact NPK ratio since it will depend on what rice you use, how much water, and how long the rice sits in that water. Basically, there are not yet studies that prove what the concentration of NPK is in rice water.
Not only minerals are transferred to the rice but also essential starches and carbohydrates. (Source)
So… what does that mean? Orchids need to have a balanced form of nutrients that they get fed all the time, constantly and repetitively. In this article (LINK) I wrote about orchid fertilizers and the 5 ways/methods to use fertilizers, I go over the amounts and doses of NPK and how to understand them.
I recommend that article to anyone who is starting orchid care just because it shows you what chemical elements and minerals your orchid needs and at what percentage (or dosage).
How To Make Rice Water for Orchids: Recipe
There are essentially two different ways that you can get this rice water.
One is to soak the rice in water, as you do to rinse it off before you cook it. The second way is to use 2x the amount of water that you would use, boil the water with rice for a few minutes, then strain off the top portion of water.
I, personally, have never used this second method because it takes too long, and I don’t like to be around boiling water.
So back to the first method: you need to rinse the rice in water and swish it around a few minutes to clean the rice grains. What comes off in the water is what you will be using in your rice water.
There is another method that I haven’t tried since I’m reluctant to add this product to my potting media. The result is a fermented rice water, but in essence, I’d be adding more fungus to my potting media (rice wine in formation). No matter how much I know that some bacteria and fungi are beneficial, I just can’t get myself to add that to my orchids. I fight hard enough against root rot to even try.
Yet I can’t write this article without mentioning it because for other household plants (and terrestrial orchids) this solution has been proven to be beneficial.
In this method, the recipe is the same except the time the rice sits in the water in a shady, cool place and the wait time is expanded to 3-4 days. Some authors say 10 days. This allows fungus to grow in the water and feed off the rice, turning this water into a fermented water.
Don’t get me wrong, I love wine, and there are many ways to make rice wine, but I just can’t get myself to try the fermented rice water. If you have tried this, please comment in the section at the end of this article and tell me how it went.
Rice Water Feeds the Orchid’s Mycorrhizal Fungi Essential Starches
The reason that this newly-fermented rice water is beneficial because orchids have a special relationship with fungus that is classified as a mycorrhizal relationship.
Mycorrhiza comes from the Greek, “Mykos” which is fungus, and “riza” which is roots. The fungus will provide the roots with all the nutrients that the orchid roots can’t digest themselves, and in return, the orchid provides the fungus with…literally nothing.
It’s the worst type of relationship possible, and all the benefits are on the orchid’s side. Once the orchid has reached a mature enough state to live on its own it can do 2 things: consume the fungus entirely turning itself into a parasite or live pacifically with the fungus and have it do all the hard work.
Think of this relationship as a young adult who won’t move out of his parent’s house but doesn’t want to get a job either. The orchid lives off the nutrients the fungus provides and gives nothing to the fungus in return.
Rice water will provide a healthy quantity of starch to the fungus in the form of carbohydrates, which it absolutely devours. The orchid roots will absorb the starch in the rice water, if they have the CAM pathways, which thick-rooted Phalaenopsis and Cattleya have. (If you are wondering, CAM is short for Crassulacean Acid Metabolism and it’s how most thick-leaved orchids process their sugars. It’s one of three ways orchids process sugars and amino acids.)
In one study, “Maltose Processing and Not β-Amylase Activity Curtails Hydrolytic Starch Degradation in the CAM Orchid Phalaenopsis”, the author states that the sugars are stored in Phalaenopsis roots as a form of starch.
This just proves that orchids can absorb starch with or without the fungus. They state that orchids that process carbohydrates using the CAM pathway “mainly relies on major nocturnal CO2 fixation sustained by degradation of storage carbohydrate such as starch to provide phosphoenolpyruvate (PEP) and energy”.(Source)
To summarize, the fermented rice water will provide the fungus inside the orchid pot the sugars and starches it needs, nourishing them. In return, the fungus will degrade the elements in your potting media and turn them into nutrients that the orchid’s roots can readily absorb, lessening the work that the orchid must do to get energy.
Even if you have a semi-hydroponic setup, which contains considerably less fungus, the fermented rice water will still benefit your orchid. The new roots can absorb starch, the older roots not as much.
In essence, fermented rice water benefits both epiphytic and terrestrial orchids; orchids that have little to no bacteria and fungus, to those that have tons of fungus (the beneficial fungus…not the types of fungus I try to get rid of).
Non-Fermented Rice Water for Orchids
Most of the articles I read made a point in saying that the fermented rice water for orchids didn’t smell or have a sour stench, but I still can’t get myself to test it. That leaves me with the second method which is the soaking for a few hours in water as a pre-rinse cycle before I cook the rice.
This method is what I use, and I’ve found it to be beneficial. Since I’m going to throw away that water anyway, it’s best just to use it on the orchids and other houseplants.
The silky, powder-like water that drains off the rice grains contain around 16 % of protein. Triglycerides and lipids come in at 10%, while starch has 9% of the composition. “Carbohydrates, inositol, phytic acid and inorganic substances are other components in rice water.”
The orchids roots will absorb this rice water in the form of starch, independent of the fungus. Starch is what provides the orchid with energy when it needs it, and the orchid can store this energy both in it’s roots and in the leaves.
Arguments Against Rice Water for Orchids
Not all is positive in the rice water debate. I’ve read some arguments that state that the orchids can’t absorb the starches in the water and need the bacteria to break them down, much like calcium needs to be dissolved into calcium-nitrate before the orchid can absorb it.
Well, that isn’t the case.
In this article published by Orchid Digest (Source), the author details how the roots absorb nutrients. She goes into a lot of detail about the anatomy of orchid roots, and I just found it to be fascinating to read. In any case, orchids can absorb starch, and after they absorb it, they store it in two locations: 1) in the endodermis of the cortex of new roots, and in the leaves—thanks to the xylem.
Starch, which translates as carbohydrates or sugar, is how the orchid stores energy. Remember the CAM pathway I mentioned above? This is where starch comes in handy.
These orchids usually live in habitats where it rains abundantly then is suddenly stops. The orchid roots dry out quickly and must be able to store the maximum amount of minerals, nutrients, and water until the next time that it rains.
The velamen on these types of orchids will absorb the starch independent of the fungus, and that starch is transferred through the xylem (if compared to the human body it would be the circulatory system of the plant) and stores sugars in the form starch. Later the orchid will use this starch, breaking off little pieces and use it as energy.
Normally, to store energy the orchid would need tons of water.
In environments where water is not promised, and the orchid doesn’t know when it will receive its next rain, the orchid made a way of absorbing sugars, transforming them into starch. Storing starch doesn’t require water, so it can economize the little water the roots collected.
In essence, when you water your orchids with rice water, the high levels of starch will be absorbed by the roots. Not only that, but they are also stored in the leaves to efficiently reduce the amount of water they need to use energy.
Is Rice Water for Orchids Starch…Or Sugar?
The breakdown of the starch provided by the rice water is done to produce energy for your orchid. Sugars do the same thing, so why not just add sugar to the water? There is a whole different debate of whether molasses or honey would have the same effect of rice water on orchid roots.
Orchid leaves photosynthesize to produce sugar—that’s their main purpose in life. But adding starch (which will eventually be reduced from some sort of sugar) doesn’t have the same effect. Orchid roots can absorb and exude sugar from their roots and control the intake of their sugar through their roots. (Source)
I wish all diabetics could do the same… Imagine if there were a way to eliminate the sugar you don’t need instead of absorbing it into the bloodstream! Anyway, I digress…)
The fungi which receive this starchy water form the pre-rinsed rice will increase the amount of CO2 in the orchid potting media along with supplemental doses of nitrogen, phosphorous, and potassium.
This only enhances their growth. According to one study done by Dr. Christopher Teh, (an expert in crop modelling, environmental biophysics, and soil conservation) senior lecturer from the Faculty of Agriculture, University Putra Malaysia, the crops that were watered with rice water showed better results than the ones fertilized with normal chemical fertilizers.
In that article, the author says, “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.”
Can you Trade Out Your Orchid Fertilizer for Rice Water?
I do not recommend trading out the rice water totally for chemically produced fertilizer since your orchid still needs other micronutrients that rice water doesn’t provide.
It’s good to have a schedule of when you added fertilizer to your orchids and keep the dosage in between the recommended limits. In rice water, we really don’t know what those dosages are. You could be overfertilizing one micronutrient while under fertilizing another.
I recommend using rice water no more than once a month and keeping your normal fertilizer schedule with the recommended 20-2-20 NPK ratio.
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