How much dolomite lime per solo cup?

I've been having a problem with my plants, growing in potting mix in solo cups, showing symptoms of too low pH. I obtained 50 lbs dolomite lime from the local ag supplier. Search online says to use 1/4 cup per gallon of potting mix.

My spreadsheet seems to say that's equivalent to 1.5 teaspoons per solo cup, i.e., 96/64. Not sure if anyone else can follow my simplistic thinking here:


How many teaspoons per solo cup should I start with? I'm thinking either 1/4 teaspoon or 1/2 teaspoon. I'd rather use less than too much, then add more over time if needed.

Are there errors in the above?

Let’s try some different math ( not saying I’m right). 1/4 cup is 3 oz. There’s 6 teaspoons in an ounce, 3 oz in 1/4 cup, at 18 teaspoons per gallon, a solo cup is 16 oz, or 1/16 of a gallon. So 18 tsp divided by 16 oz is 1.125 tsp per 16 oz.
My question is why do you think the potting soil is too acidic? That’s not real common in soil grows. What’s the potting mix got in it?

Isn't a quarter cup 2 ounces? And teaspoons are like 5ml, so wouldn't that be hundreds and hundreds of tsp per gallon? Maybe I'm high, lol. Sorry to interrupt.

Rsawr said:

Isn't a quarter cup 2 ounces? And teaspoons are like 5ml, so wouldn't that be hundreds and hundreds of tsp per gallon? Maybe I'm high, lol. Sorry to interrupt.

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You’re right, 1/4 cup is 2 oz.

At 1/4 cup dolomite to 1gallon soil, that’s 12 tsp Dolomite per gallon (72 ml).also 16 oz is 1/8 of a gallon, not 1/16, shouldn’t do this when stoned. Crap never mind, the op is correct at 1.5 tsp/16 oz.

Phytoplankton said:

My question is why do you think the potting soil is too acidic? That’s not real common in soil grows. What’s the potting mix got in it?

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I've documented it in my grow journal, the first link in my signature. This is the first time I've recycled potting mix. It's Kelloggs Palm Cactus and Citrus and sand that has been boiled water treated (to kill insect eggs), then earthworm castings are added. Summary: My plants had a severe Ca deficiency and low runoff pH, I've solved the problem with dissolved gypsum and keeping nute pH over 7. A new problem is nute pH is no longer stable in storage with the dissolved gypsum added, and I don't have the time or desire to pH nutrients every time I irrigate. So, I'll be adding gypsum and a small amount of dolomitic lime to the solo cups. Your answer of 1.25 teaspoons is close to 1.5 I got with my math.

Confused- are you are trying to amend a solo cup worth of soil ?

A solo cup of fresh bagged soil is already buffered.
What kind of issues are you having ?

Dolomite lime is basically cal mag - calcium magnesium carbonate.

Budzbuddha said:

Confused- are you are trying to amend a solo cup worth of soil ?

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Yes. I figured I'd topdress. The plants are already growing in it. I think the problem is the recycled mix from a prior grow. I learned long ago not to recycle potting mix, but wanted to try again.

simpleleaf said:

I've been having a problem with my plants, growing in potting mix in solo cups, showing symptoms of too low pH. I obtained 50 lbs dolomite lime from the local ag supplier. Search online says to use 1/4 cup per gallon of potting mix.

My spreadsheet seems to say that's equivalent to 1.5 teaspoons per solo cup, i.e., 96/64. Not sure if anyone else can follow my simplistic thinking here:

	cup​	1/4 cup​	oz​	teaspoon​
1 gallon →​	16​	64​	128​	768​
16 oz plastic cup →​	2​	8​	16​	96​
				1.5​

How many teaspoons per solo cup should I start with? I'm thinking either 1/4 teaspoon or 1/2 teaspoon. I'd rather use less than too much, then add more over time if needed.


Are there errors in the above?

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You get an A+ from me. I follow your logic. But I must admit at first I was like

As an update, I used 1/4 teaspoon per solo cup of dolomite lime which correlates to 2 teaspoons per gallon (rather than the 1/4 cup per gallon I'd seen online and mentioned above in my first post in this thread). That seems to have been a good amount to use, my runoff pH is now almost the same as nutrients, and that's been true through several irrigations. My plants are looking better. What I don't know yet is how long it will last. If runoff pH creeps down over time, I can easily topdress with a little more.