Adding Dolomite Lime for Orchids: Why, When, and How Much

Once you step into the waters of orchid care, you learn that your orchid needs fertilizer ever so often to keep it healthy. Nitrogen, phosphorous, potassium, calcium, magnesium, boron, and manganese are the most common nutrients that you can offer your orchid.

Yet somewhere you’ve heard of adding dolomite lime to your orchid. What does dolomite lime do? How does it affect your orchid? In this article, I’m going to go over a few specifics of dolomite lime and how orchid care can benefit from adding it to your potting media.

Dolomite lime for orchids raises the pH in the potting media, correcting the overly acidic soil. It contains calcium carbonate and magnesium, two elements that orchids desperately need to grow. Dolomite lime, known to reduce fungal attacks on orchid leaves, also reduces the toxicity of iron, magnesium, and manganese in your orchid pot.

Coffee and Orchids
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 Dolomite Lime and Orchid Care

So how does that all work? What exactly is Dolomite Lime? Before I go any further into this article, I must give my advanced “disclaimer”. I’m not a chemist or a biologist.

In fact, I hated chemistry in high school and struggled to pass. My “real job” is a theologian, and you can read about in my about page.

Years come and go, and we all change. Little did I know, one day I was out playing volleyball with my friends on the beach, and years later I was rearranging my orchids inside to get the best filtered light. What I hated back then, I find “somewhat” fascinating now. Except my deficiency in understanding chemistry is still present.

The following is a gathering of my notes and what I have found on the subject. It doesn’t mean that it’s right. That means even though all my research is based on factual data, I still might be wrong. That is why I’ve linked to all the articles I used as sources, and you can read the data for yourself. I just wanted to clear that up before we go any further…

What Is Dolomite Lime?

Dolomite Lime is a natural product (rock) made of limestone. When you purchase Agricultural Lime, dolomite lime is just one of those many types of lime that encompasses that term.

To better understand lime, I want you to envision a line with 2 endpoints. On the left endpoint, write Calcite, and on the far-right endpoint, write Magnesite.

These are just a few of the types of lime that agricultural lime encompasses, but they are the most useful to orchids. In the very middle of this line, write Dolomite.

Let’s look at one of the endpoints first: Calcite Lime. Calcite (100% – CaCO3) is made of a high calcium-concentrated limestone, called calcite. As you have guessed, it will raise not only the pH in your orchid pot but will also add an extraordinary amount of calcium to it. This is an increased benefit, because most NPK orchid fertilizers do not add calcium. Yet, it can add too much and be an overkill. (Source)

On the other endpoint, which I might emphatically add is also limestone, but instead of the high calcium concentration in it, it contains Magnesium in high doses. That’s why it’s called Magnesite (100% – MgCO3).

This is especially useful for orchids because Magnesium is one of those nutrients that is overlooked but extremely necessary in orchid care. If your orchid is lacking Magnesium, then adding Dolomite Lime is necessary.

The more you bend to one of these end points, (Calcite) the higher the calcium and the lower the magnesium, or (Magnesite) the lower the calcium and the higher the magnesium. Both magnesium and calcium will still be added no matter what type of agricultural lime you use, but the percentages and proportions will dapper off towards one side. (Source)

Let’s go back to that imaginary line you drew. In the middle you should have written Dolomite. This is an imaginary neutral 50-50% of both calcium and magnesium. Now let’s divide the line between the endpoint of Calcite and the midpoint of Dolomite. On this marker, you’ll write dolomitic lime. Yes! This is where we are headed.

That means that dolomitic lime has more calcium than magnesium, but still raises the pH in your orchid pot, fights off fungal infections, strengthens cell walls, and keeps the ratio of Calcium to Magnesium in balance.

Image Credit: © 2021 Orchideria.  All Rights Reserved. 


Dolomite Lime Adds Both Magnesium and Calcium

Now that you know what Dolomitic Lime is made of, let’s look at how that interacts with your orchid. Mainly I’ll be focusing on the increased percentages of Calcium and a little added percentage of Magnesium in your orchid. Except you can’t really focus on one nutrient and eliminate all the rest. They all work together in a group as one nutrient and mineral interact with others.

Calcium is an immobile nutrient and is extremely important for all orchid growth. That means every time you water and add calcium, the roots will soak it up and it will travel through the orchid to its endpoint.

Once there, calcium will interact with the orchid cells and make them stronger. If the orchid detects that a certain part of the plant doesn’t have calcium, then it cannot, I repeat, cannot, move calcium around inside the leaf and stem to where it is needs. The orchids rely on the next rain that contains calcium to get a new supply.

I have a YouTube video about magnesium deficiency (and it’s relationship to calcium) that you might want to see later, if that’s something you’re interested in. (Link)

Anyway… Calcium is like a mule. It’s slow, but it’s dependable. The orchid will get its nutrients, as they hop on top of the Calcium’s back for a ride, making calcium even slower.

Many nutrients are available, but they need to attach to calcium to be taken around to their endpoint. From there, these freeloader nutrients can move to anywhere they like, yet calcium can’t.

If you have calcium, you also need Magnesium. Most plants need a ratio of 4 to 5x more calcium than magnesium, but I’ve also read that the ratio can be up to 6x. The problem here is that both Calcium and Magnesium must face a huge bully to get where they’re going: Potassium (K).

Potassium works as an antagonist to both, and that is what is popular inside most orchid fertilizers. Potassium is necessary, but in strong doses, it wipes out the other nutrients.

Dolomite Lime Raises the PH in Your Orchid Pot

Dolomite comes to save the day as an extra calcium and magnesium supplement for your orchids, while it also raises the pH inside of your pot.

One of the first things that we learn as orchid growers, besides how to water properly, is how to choose the best potting media. If you are treating your soil like dirt, then your orchid won’t appreciate you or the potting media. You need to provide the best for your orchid, and it will repay you with wonderful blooms. (Source)

If you don’t want to pay for meters of instruments to measure the pH, one way to verify is to look at the roots. If every single root is trying desperately to avoid the potting media, that probably means something is off. That “something” could very well be the pH inside your potting media.

This happens because most potting media (well, the most common) is sphagnum moss and orchid bark. Both these break down quickly and will start to decompose in 2 years.

Even though these are the most common, any organic material that you use will decompose in time. If you don’t renew the potting media, it will continue to decompose at an even higher/faster rate, lowering the pH inside the pot. Your orchid pot now is too toxic for the roots—way too acidic to live in.

Dolomitic lime will “sweeten” the orchid bark by raising the pH slightly. The goal here is to reach between 5.5 and 6.5.

If you are reading this article but do not care about orchids, (you are a plant person but other household plants) then I do have to mention one thing. Most plants prefer a higher pH, not a lower one. Most orchids are the exception. Most plants will love lime in their pots, since acidic media just turns their leaves brownish-yellow, as in a crispy burnt look.

Dolomitic Lime Sweetens the Orchid Potting Media

There are 3 groups of orchids that benefit from adding Dolomitic Lime.

The first group is the orchids that have an extremely low pH, almost around 5.0. With one application you can raise the pH in the orchid pot and bring that up to around 5.5 in 6 months.

This isn’t the best though because you have tackled the solution, but the problem remains.

What caused your orchid potting medium to go so low? Why does it go “sour” all a sudden? This usually happens because the orchid bark needs to be changed and is slowly decaying inside your pot.

Another reason is that the sphagnum moss was a cheap brand—it usually decomposes first before the orchid bark. If you tested your potting media and found out that the pH is way too acidic, it might be a good idea to repot.

The third reason the orchid pot could be low on pH is the water you are using. If you know for sure that the orchid bark and sphagnum moss are new and recently changed, then you need to test the water. That could very well be the problem inside your pot.

Lithophyte Orchids Benefit the Most From Dolomitic Lime

The second group of orchids that can benefit from adding dolomite lime are all those that grow naturally on rocks. These are called lithophytes, and they attach to limestones boulders on the sides of waterfalls and humid cliffs.

During thousands of years, rainwater trickles down the side of these calcium carbonate highlands, extracting the dolomite lime (and many other minerals) that aid the nutrition of the orchid roots.

Here’s the catch: with what we know in orchid care today, you can attach an orchid to almost anything. Clay pots, terrarium twigs, seashells, oysters, and anything that is immobile.

To really know what orchids are truly lithophytes, you’ll have to look up your specific orchid and see how it grows in nature.

That might take a little research, but most growers and sellers will have a few that pop into their minds.

From what I found, the following orchids are lithophytes in nature (or can also be lithophytes, not being exclusive). These would be the first to benefit from biannual applications of Dolomite Lime.

Lithophytes in Nature

Angraecum

Bifrenaria

Brassavola

Bulbophyllum

Corrybas

Dendrobium

Dockrillia

Encyclia

Epidendrum

Goodyera

Laelia

Peristylus

Paphiopedilum

Pleurothalus

Podochilus

Zeuxin

The third group of orchids that benefit from a biannual dose of dolomitic lime are terrestrial orchids or semi-terrestrial orchids. They will not get their daily dose of lime from rocky, mountainous cliffs, but from the rocks laying around in the soil. (Source)

These orchids naturally have a higher pH, tending to be more alkaline. That’s an important part of growing orchids that hardly anyone talks about.

If you have a Phragmipedium, cypripedium, or paphiopedilum, then that is an important note to know. Lady slipper orchids need a higher pH than normal. You can read more about their care in this other article that I wrote.

Dolomitic Lime Fights Off Orchid Fungal Infections

Fungal infections in orchids are horrible. I hate them with a passion as I stare down at my poor roots and leaves decayed beyond repair. Some orchids are more prone to fungus, such as Cymbidiums. In fact, Cymbidiums are notorious for having all kinds of strange things attacking their leaves.

They are semi-terrestrial, and their potting media is special. It can’t be just orchid bark and sphagnum moss. (If you want more information on what type of potting media to use for Cymbidiums, I wrote this article that might be of some help.)

But being so close to the ground and liking a higher humidity, the fungal growth is almost a “given”. If you haven’t dealt with that before, then it’s a “given” that you will soon.

One of the many things that attack the orchid leaves are fungus.

Dolomite lime does eliminate fungus when applied as a powder. You can also achieve this goal by adding crushed oyster shells.

Not only that, but dolomitic lime also reduces the toxicity of iron (if you happen to add too much), aluminum, and manganese. So overall, it’s hard to find things to avoid about its use in the orchid pot. The only advice I can give you is not to add too much. (Source)

You can raise the pH so much that your pot becomes alkaline, and Phalaenopsis, Cattleya, Dendrobium, and many other orchids don’t appreciate that.

Too Much Dolomitic Lime to My Orchid

It can happen that what I just mentioned above happens: I knocked over the dolomitic lime and now there’s lime everywhere. That’s something I would do too, so don’t feel bad. It happens.

The bad part is that the orchid potting media will now be so full of calcium and magnesium that those minerals will block the others from properly functioning. In this case, you’ll need to add a product called Gypsum, which is sulfur (S).

Sulfur will act as a counterpart to both magnesium and Calcium, lowering the effect of both. Gypsum will also lower the pH in the orchid pot, so you’re covered there, too.

Yet this is a good point to emphasize: calcium and magnesium work together (dolomitic lime) to raise the pH, but if it goes too high, add gypsum to bring it back down and neutralize the effect. Magnesium is the mineral that has the biggest effect on pH, more so than Calcium does.

Some Limes Don’t Work Well With Orchids

Dolomite Lime can be purchased in a variety of forms: slate lime, pelletized, pulverized, powdered, and hydrated lime. Avoid slate and hydrated; there are downfalls with both. You want the pelletized version or the granulated, powdery version.

Pelletized lime can be expensive, especially since it’s hard to find it in smaller bags. The good side of working with this is that it isn’t dangerous or hazardous. It’s usually sold to farms and plantations, where huge bags are in demand. For a hobby such as orchid care—I’m assuming you don’t have 100 acres of orchids—it’s hard to find it in small quantities.

Whatever you use, note that the smaller the size of the particles, the faster it will act in raising the pH and getting that orchid pot to a sweet 6.5. The larger the pellets, the longer it will take to degrade. This translates into 6 months or more.

The pelletized dolomite lime is held together by a water-bond polymer and degrades as soon as water touches it. This means that it breaks down after you water it. The bond is weak enough that the lime will then move through your orchid pot.

The hydrated lime and burned lime are both hazardous to work with. You’ll need to wear gloves and goggles, and as soon as you spread it around your orchids, you’ll need to water it down to prevent foliar damage.

Hydrated lime turns into a soggy, yucky, sticky, slimy, and overall nastiness when watered. This happened because the bond that holds the lime together is not a water-bond. This makes a royal mess inside your orchid pot, so just stay away from it.

How Much Dolomite Lime do Orchids Need?

The instructions say for 1,000 square feet of loamy soil that is anywhere from 5.5 to 6.0, you’ll need to add 25lbs of lime.

As you might have noticed, the amount of lime depends on how much you want to increase the pH of your soil. No application of lime will immediately increase the pH by a 2 or 3 since it’s a gradual increase and takes a horrendous amount of time.

Depending on the pH in your orchid pot, the increase can be 0.5 over the next several months and it will need to be reapplied after 6 months. If you add too much during one application, the dolomite lime will overtake the other minerals and nutrients in the pot, not allowing them to function properly.

This dominance will eventually kill your orchid, because orchids need a whole variety of minerals and nutrients, not just dolomite.

If your case is severe, you can add ¼ t4easpoon every 3 months to the orchid pot. The immediate result—as immediate as orchid care and growth goes—is the leaves will darken even when given the right light requirements.

If you are wanting to buy Dolomitic Lime, then this is the one I use. (Affiliate Link) I found its cost/benefit ratio to be very good. There are other brands that specialize in orchid care (Repotme), but there’s was more expensive (or at least during the time I wrote this article) and it is essentially the same product in the bag.

Don’t Stop Learning!

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I don’t spam, but send emails out bi-monthly with some curious topics of interest. If you want more information, click here to go to a specific page on this website where I explain it more in detail.

Orchid Fertilization

Also, if you are looking for an orchid journal to keep your notes specifically about orchid care, check out my 2 solutions for that on this page. If note-keeping isn’t your thing, then there is a free excel spreadsheet that you can download. Click here for more information on how to do that.

In all, I hope this article helped. If it did, please leave a comment below. If I said something that is totally off, please mention that too, and I’ll fix it. Thank you so much for reading this far, and happy cultivating!

Signature Amanda Matthews


Amanda Matthews

Amanda Matthews is a theological professor, author, pastor, and a motivational speaker. She's passionate about spreading hope and teaching. Her hobbies include biking, cultivating orchids, and exploring nature trails. She now lives in Kansas, while raising her two children. To read more, go to https://orchideria.com/about-the-author

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