First, before we get into the grit of this post, if you’re wondering “Why not use Phosphoric Acid instead?”—I’ll explain why not. Over the past two years I had been using phosphoric acid to lower the pH of my plant-nutrient solution. And that seemed to work well…until it didn’t. In late spring of 2019, I purchased a ‘poisoned’ product of pH Down (phosphoric acid) from a local greenhouse and whatever was in that bottle setback about half my collection of over 300 plants—it ended up killing over 25 plants and even now 4 months after I’ve stopped using it, I’m experiencing a halo affect of problems. Though thankfully they are progressively becoming less and less. If you want to know more about that debacle, you can read the story and details here.
Why this recipe? Despite that setback, I still understand the importance of acidifying my alkaline tap water for maximum nutrient availability. I do this for my orchids, aroids and pretty much all of my houseplants so I needed to find a more reliable way to lower the pH of my tap water and 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 work with acids that were either safe for human consumption and/or are produced by plants, bacteria, or natural processes.
Does this recipe work when used? I believe so. I have been using this ‘pH Down’ and have been following a 4-week cycle on my entire collection for over 6 months now. The results are better than I expected, but it could also just be that my plants aren’t being poisoned anymore. That said, some of my slowest growing plants like the miracle berry have doubled in size in the last few months. Others like my orchids have produced an abundance of new roots and my “jungle aroids” have produced their largest leaves yet. If you want to see my collection of plants for yourself, you can hop over to my instagram feed.
Please note: I am not recommending you or others use this recipe. It’s been working well for me so I’m publishing it for those who follow my blog and want to know the details of how I grow my plants. I also don’t think that this is some magical recipe that will make your plants explode in size — there are a lot of cultural parameters I have learned to tweak over the years to improve my ability to grow plants…pH-adjustment is just another one of those things I alter for better growth (along with light, potting media, watering practices, etc).
Without any more blabber, here’s my pH Down recipe…
Organic pH Down Recipe for Plants
*Note: I use heaping table/teaspoons; not perfect measurements.
- 1L, Empty water bottle
- 1.5oz, Apple cider vinegar
- 0.5oz, White vinegar
- 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)
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. Be sure to re-test the pH when using if stored for longer and remake if the acidity decreases.
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 follows two acidic waterings, followed by two non-acidified waterings. Sometimes I use different fertilizers (12-8-8 in the spring, 20-20-20 in the fall, by typically I use MSU orchid fertilzer for all my plants). This is the monthly cycle I follow:
- Acidified water (to 5.8pH) + fertilizer 1/2tsp
- Acidified water (to 7.0pH) + fertilizer 1/2tsp
- Tap water (7.9pH) flush AKA leach (no fertilizer)
- Tap water (7.9pH) + fertilizer 1/4tsp (reduced)
- Once a quarter (every 3 months): Acidified water + fertilizer + eggshell (optional – see below)
/// Disclaimer: from here down is new experimentation; I don’t yet recommend you follow this…
Calcium Supplementing 4 Times A Year
Eggshells Are Just as Effective as CalMag (if you’re adding an acid)
I combine apple-cider vinegar, citric acid & 1/4 eggshell (pulverized to powder – ~3g) in a 1L bottle. The eggshell dissolves resulting in calcium acetate (+whatever micro nutrients are also in an eggshell)—a form of calcium plants can use. I’ll then add a bit more acid to the bottle (from the recipe above), so that 2 capfuls in a 4L jug of tap water lower the pH to ~5.8. I’m only using this calcium solution once every 3 months–but specifically in mid spring when the phrags and other orchids are actively growing. The first watering immediately following this calcium does, is just a flush of tap water with no fertilizer or nutrients.
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 that 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. 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), vinegar (acetic acid), along with other byproducts of natural decomposition (gluconic, glucuronic, citric, L‐lactic, malic, tartaric, malonic, oxalic, succinic, pyruvic, and usnic acid) 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 – but, 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 and they show up 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 it’s because it’s 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? By bacteria fermenting the cabbage leaves! As the sugars in the leaf are consumed by the bacteria the result is acetic acid – 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 produce acids and are conveniently happening in nature on trees, in the dirt, on rocks, 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 acidity is low, while the substrate pH is high, 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?