Update 2022: I have stopped using “organic acids” as pH Down and I am not recommending you apply these to your collection without first testing it for a few months on replaceable plants. In general, this application did work alright for some plants (which is why I had originally published this post); however, over time I found that the various forms of vinegar (white, apple cider) and also malic acid, eventually negatively affected specific plants. Vinegar specifically seems like a bad option and I wouldn’t recommend it to lower your pH—it’s too easy to irreversibly damage roots. I also have some concerns about the quality of citric acids out there—I suspect some brands have more sugar than others and if that’s true, it could lead to an increase in fungal or bacterial issues.
I don’t think that this is some magical recipe that will make your plants explode in size — it was just an experimentation to see if I could find something more reliable than phosphoric acid. Along with pH, there are a lot of cultural parameters I have learned to tweak over the years to improve my ability to grow plants (light, potting media, watering practices, etc)…pH-adjustment is just one of those things I adjust for better growth.
So please please please if you’re going to try this…proceed with extreme caution and do not apply to your whole collection.
Why did I start experimenting with “organic acids”? For the two years prior to writing this post, I had been using phosphoric acid to lower the pH of my plant-nutrient solution. That worked well—until I switched the brand I was using. In late spring of 2019, I purchased a new brand of phosphoric acid from a local greenhouse; whatever was in that new brand setback about half my collection of over 300 plants and ended up killing well over 50 plants. For months after I’ve stopped using it, I experienced a halo affect of issues ranging from setback roots, leaf spotting, leaf colour problems and general slow growth. Thankfully those issues have progressively faded, but even a full year after the whole thing, some of my most-prized orchids were still recovering. If you want to know more about that debacle, you can read the story about my pH Down blunder, here. You may be wondering, “why not switch back to the original pH Down brand that you were using before?” well now I have, but first I wanted to try some of your more accessible acids (like acetic, citric and malic acid). pH Down by General Hydroponics is what I use now and I never had issues with that brand.
Why this recipe? Despite the setback I had with phosphoric acid, I still understand the importance of acidifying my alkaline tap water in an effort to offer maximum nutrient availability. In short, it helps them grow faster and larger as key nutrients (like nitrogen) are more accessible to many types of plants. One could use RO or distilled water instead of tap water; however, I have a LOT of plants and I have been pH-adjusting water for my orchids, aroids and pretty much all of my houseplants for 3 years now. I just needed to find a more reliable way to lower the pH of my tap water and that’s why I turned to food-grade products (which are tested/approved for human consumption). I had heard many people use citric acid, vinegar, and a few other options, so I decided to explore those acids which were either safe for human consumption or are produced by plants, bacteria, or natural processes.
Does this recipe work when used? It did sort of but I modified it over time and eventually had to stop because a couple of my most prized plants responded poorly to it. I was using this ‘pH Down’ on a 4-week cycle across my entire collection—a cycle that involves regular tap water for three waterings, followed by a pH-adjusted feeding (so the pH swings on a monthly basis). The results were better than I expected, but it could also just be that my plants weren’t being poisoned by whatever that phosphoric acid product was. Some of my slowest growing plants like the miracle berry had doubled in size only a few months after using the organic acids but then they really slowed down later in the year. Others like my orchids produced an abundance of new roots and some of my “jungle aroids” produced their largest leaves ever, but eventually started showing issues like leaf burning and short roots. I’m a stickler for the details of my plants, so it wasn’t like a catastrophic issue…you can see my collection of plants for yourself on my instagram feed.
Without any more blabber, here’s my organic acid pH Down recipe…
Organic pH Down Recipe for Plants
*Note: I use heaping table/teaspoons; not perfect measurements.
- 1L, Empty water bottle
- 2 tbsp, Citric acid
- 1 tsp Humic/fulvic acid (Optional or used every other month)
- Water; or
Carbonated tap water – via SodaStream (optional…but provides carbonic acid)
UPDATED July, 2020: I had attempted the following acids but stopped using them after a few plants responded poorly.
- Apple cider vinegar (.5 – 1oz) – some plants responded negatively to this after a few applications.
- White vinegar (1 – 2oz) – seemed to work fine in general, but after a couple months I noticed some of my more sensitive plants (such as Macodes petola) started to develop slight leaf yellowing. I gradually decreased the amount of vinegar used over time and the spotting stopped, so I have entirely stopped using vinegar.
- Malic acid (not recommended) – I stopped using this early on because it caused severe leaf spotting in select plants after a single use. It set back a few of my seedlings too. Not recommended.
Directions to Make pH Down
- Add all acids to the 1L bottle w/ a funnel.
- Top-up bottle with tap water (carbonated if you have a sodastream).
- Shake & use.
** This can be stored for short periods of time. Some have said citric acid loses acidity over time; but from my experience, it still worked after one month. I would be more concerned about bacteria growing in your solution; so if you’re going to store it for more than one watering, make sure to refresh your solution and bottle after a couple watering cycles.
What you need to use the pH Down
- Pre-mixed acids in 1L bottle – this is your “pH Down”
- Fertilizer (I use MSU Orchid Fertilizer)
- A jug for combining fertilizer, your pH Down, and tap water (I use a 4L/1Gallon juice jug)
Directions For Using pH Down When Watering Plants
- Get a pH meter or litmus paper.
- Place watering jug in sink.
- Add fertilizer (1/4-1/2 tsp per gallon of water is generally good) to jug.
- Shake the “organic pH Down” vigorously before each use.
- Add a capful of “pH Down” to 1 gallon jug, directly into fertilizer crystals.
- Turn on tap and fill jug with tepid-temperature water (it should feel slightly cool, but not warm to your touch – human body is 37•C…it should feel slightly cool to you, so not cold or warm)
- Stir a few times with large spoon (optional)
- Test pH
- If pH is 5.5-6.5 – Good! Use on plants as you normally would water them.
- If pH is over 6.5 pH – add a second capful, retest pH, and either just use 2 caps or adjust the recipe for more acidity next time.
- If pH is lower than 5.5 pH – dilute 1L bottle by 1/2, remake & test fertilizer jug with new diluted version, and adjust the recipe next time.
- Use pH-adjusted fertilizer water on plants
- Spray the top of the potting media until the water starts to come out the bottom. You may want to read these 4 houseplant tips for some awesome foundations plant care concepts that have made me a better grower.
- You can also foliar feed by spraying the leaves.
Fertilizer & pH Cycling – Don’t Acidify ALL THE TIME
My watering routine is currently to alternate between one acidified watering and one non-acidified watering, and I gradually lower the fertilizer application over the 4-week cycle. I believe this will prevent any chance of acidity buildup in the substrate. If using alkaline water can result in pH climb over time from precipitates, you could imagine that using citric acid (a soluble crystal) to water could also result in a buildup of citric acid in the media, dropping the pH a bit lower each time. Maybe citric acid is broken down, but I think some people missunderstand the term “weak acid” when applied to acids like carbonic and citric acid…it doesn’t mean they are weak in their ability to exist; a week acid just holds on to the electrons more than a strong acid which freely donates electrons making the acid strength stronger. At anyrate…to prevent any chance of pH creep in either direction, I cycle the acid application with regular alkaline water to err on the side of caution. This is the monthly cycle I follow:
- Acidified water (to 5.8pH) + fertilizer 1/2tsp
- Tap water (7.9pH) + fertilizer 1/4tsp (reduced)
- Less-acidified water (to ~7.0pH) + fertilizer 1/4tsp (reduced)
- Tap water (7.9pH) flush AKA leach (no fertilizer)
- I have used different fertilizers over the years (12-8-8, 20-20-20, etc), but now I just stick to MSU orchid fertilizer for all my plants because it includes micronutrients and because I know the product is pretty consistent.
- I don’t need calcium (because my tap water already has a lot), but if you’re growing plants from limestone regions of the world (like from the Peruvian mountains, or Malaysian limestone outcrops), then a routine calcium boost may be helpful. *Optional and for select plants only: Once every 6-8 weeks: Acidified water + fertilizer + eggshell (see details below)
/// Disclaimer: from here down is new experimentation; I don’t yet recommend you follow this…
Calcium Supplementing for Plants Adapted to Calcium Rich Soils
Theory: Eggshells are just as effective as CalMag (if you’re adding an acid)
Eggshells are loaded with calcium—they’re literally made up of calcium carbonate and a bunch of other minerals—similar to oystershells and limestone found in rock formations in some mountain regions. Calcium carbonate is not easily dissolved in water—unless you add an acid. To release those minerals from an eggshell, you can add vinegar, citric acid, or carbonic acid & 1/4 eggshell (pulverized to powder – ~3g) in a 1L bottle. The eggshell dissolves resulting in calcium acetate, calcium citrate or calcium bicarbonate (+whatever micro nutrients are also in an eggshell)—all forms of calcium which plants can use.
If you take a capful of the calcium solution and a capful of your pH down, then you can still lower the pH of your tap water to ~5.8, while also increasing soluble calcium.
Should you do this, the first watering the week following this calcium application should just be a flush of tap water with no fertilizer or nutrients to clear out any residual calcium before you start your standard feeding.
Eggshells have value for plants
A hotly debated topic, some people recommend eggshells, others argue against their use in the garden. For me, the science is pretty cut and dry. Eggshells can be valuable. They’re made of calcium carbonate and release calcium under acidic conditions – and they can buffer the pH if the water or potting media becomes too acidic or too low in calcium—that’s a win especially if your water is too soft or too pure (ie. RO water). If the water is alkaline or already high in minerals, then the eggshells won’t dissolve (unless you add an acid like vinegar or citric acid). In nature, rain water (carbonic acid) along with other byproducts of natural decomposition (acetic, gluconic, glucuronic, citric, L‐lactic, malic, tartaric, malonic, oxalic, succinic, pyruvic, and usnic acids) all naturally dissolve calcium carbonate making new soluble (and plant-usable) forms of calcium. Bacteria and fungi consume decaying materials, produce those acids and decrease your potting mix pH. Adding eggshells can prevent the pH from diving too low and they provide calcium in the process. So…you can either add them directly to your potting mix (which means eventually they kind of become a bit of a sludge) or dissolve them in a weak acid and add them to your water (at a very dilute ratio).
Why add eggshells? For Calcium! For plant health! For good leaves, roots, and growth.
Calcium is a vital macronutrient that plants need but it’s non-mobile (the plant can’t reposition it from old tissue), so you have to continuously provide it as the plant grows. Calcium deficiencies in plants are common especially when growers use inorganic potting media, or a potting media which is low in calcium (like peatmoss or bark). A calcium deficiency typically isn’t immediately obvious, but instead presents as secondary problems such as: fungal and bacterial infections (AKA ‘leaf spot’ and root/leaf/crown rot) and pest problems – plants use calcium internally as an alert/response trigger to deal with pests and because it’s a fundamental building block of the cell walls, it’s integral to the plant’s health and resistance to pathogens. Calcium is also rarely included in synthetic fertilizers, so eggshells are a quick and easy way to feed your plants calcium naturally.
Consider this test for yourself
Science experiment: Take a 16oz glass of vinegar and put an egg into it and leave it for 24h—the eggshell will completely dissolve overnight as the calcium carbonate is converted to calcium acetate.
But is vinegar an ‘natural acid’? Yes – and you can read all about how vinegar is made here. But do you know what sauerkraut is? It’s pickled cabbage. Do you know how it’s made? Fermentation! By bacteria and yeasts converting sugars in the cabbage leaves to alcohol (which oxidizes to become acetic acid), or by directly producing acetic acid in the case of some bacteria – AKA ‘vinegar’ – and pickled leaves. Aerobic decomposition of sugars in nature (like when leaves, fruit, or tree sap decompose) produce acids too. If you’ve ever fermented kombucha (tea leaves & sugar) or made wine/beer the same thing happens. All of those processes that drive fermentation for our foods, also produce acids at large-scale naturally—and it’s happening everywhere in nature…on trees, in the dirt, on rocks, on fruit hanging on trees, on leaves, all over the place in a never-ending cycle of decay and acidification.
Is carbonated water natural? Kind of…when water evaporates and condenses into clouds and rain, it interacts with the atmosphere, creating carbonic acid. Rainwater has a pH of 5.5 because of carbon dioxide and it is a catalyst for breaking down calcium carbonate in nature. It’s how erosion works and is often why plants can grow in highly alkaline areas like the Rocky Mountains and limestone regions of Malaysia and the Andes in South America—because the rain is acidic and the earth pH is alkaline, it creates a pendulum of pH variation ensuring the plant can get access to nutrients and thrive in more alkaline conditions.
Carbonating water (with a soda stream) is a rapid way to create carbonic acid in our homes and it will drop the pH of your water to about 4.5pH. Beware: if you’re buying bottled carbonated water, make sure it’s <10ppm total dissolved minerals – sometimes companies add sodium to their sparkling water (12mg/L [Perrier], 32mg/L [Pellegrino] to 118mg/L [Grolsteiner]).
Test it for yourself: take a glass of water, carbonate it, let it go flat. Test the pH. Drop an eggshell (measure the weight first) into the water overnight. In the morning, test the pH again, and check the after weight measurement of the eggshell. You’ll see that it lost mass and the water pH increased.
Want to know more about eggshells?