Uses of Dolomitic Lime
 

Recently there have been some discussions regarding the use of Epsom Salt (MgSO4)on certain orchids. Others have recommended the use of Ca as part of the food mix and the MSU formula contains Ca along with other "stuff". I found a product called "Garden Lime" made by Espoma. Its composition is:

Ca ~ 21%
Mg ~ 10%
CaO ~ 29%
MgO ~ 17%
CaCO3 ~ 52%
MgCO3 ~ 35%

In small quantities think it would be safe to use, like 1/2 t per gal? This is just a guess/starting point. And it is something to use maybe once a month or so. What are your thoughts, please.

1/2t per gallon is quite a bit, these are normally found only in trace quantities. I can't think of any specific reason not to use them, but be sure to check the pH of your mix to make sure it's reasonable.

Howard, it also depends on the genera you grow.
My Cymbidium feeding program includes magnesium sulphate, calcium nitrate and a well balanced medium nitrogen content hydroponic fertilizer with all the usual macro and micro nutrients.The calcium nitrate is always fed on its own as it tends to combine with some of the chemicals in the hydroponic feed to form calcium carbonate which the plants find difficult to use.
Next season I am going to add either ammonium nitrate or potassium nitrate so as to increase the nitrogen content during the growing season .
I would prefer to use ammonium nitrate but some folks decided to use the stuff to blow things up, as a result it is no longer available!

Des

I have used a tablespoon of Dolomite lime / gal in my cymbidiums mix & topdressed a tblspn each year. I didnt see any problem.It helps buffer the media so that it doesnt go too acid. With the fertilizer regiment I use the media stays in the 6.8 to 7.2 pH range - using the soak and check the runout method. The calcium and mag doest release unless the pH starts to drop. I think you will find that cymbidiums get dead roots at pH below 6.2 or at least I do the release gives me the buffering I want. I have stopped the topdressing the past year as the crushed oyster shells I also add seem to last and give me the same effect. It all goes together of course - Am using Suncote 15-8-11 16 month controlled release fertilize and add a pinch of 6 month time release Calcium Nitrate in the spring application 1 tbl sp / gal pot and give the plants a shot of Cal Mag fetilizer (have to get the numbers another day if anyone is interested) after heavy rains from July to October. Thats for cymbidiums -

There has been some work that indicates that the plants need both Ca and Mg - together - for the maximum benefit, but as was said, it's in fairly low levels.

Adding dolomitic lime to your potting medium or fertilizer solution can make the environment SO alkaline that it will harm the plants.

Ray I have measured the PH of dolomite lime at 7 which is neutral,I find that it helps to keep the PH up when the media turns acid and in doing so extends media life . What it wont do is lower a high PH ,a problem I recently experienced due to our tap water PH jumping from a norm of 8 to as high as 10! All this happening while I was in OZ for 6 weeks . It has been quite a struggle to drop the Ph to below 7 again . At above 7 my plants were struggling Once I had dropped the PH to below 7 I could see the plants pick up almost overnight
I originally started including lime in my media mix when I noticed some of the top Cymbidium growers in OZ doing this , I have since found that many of the top growers in the USA not only add lime but also gypsum .
If you think I am wrong about this I would like to hear your comments .
Regards
Des

Des,

We're really talking about three things: nutrition, pH and alkalinity.

Yes, calcium and magnesium are important nutrients, but as I said before, not in large amounts.

Yes, it is important to keep the pH below 7, with 5.5-6.5 actually being nest for most orchids.

Alkalinity, on the other hand is a lot stronger of a factor than even pH, and dolomitic lime, which is a Ca-rich calcium magnesium carbonate, is pretty strong in that regard. Think of it as the ability to neutralize acid. Please read this: http://www.firstrays.com/PDF/Part%20...ertilizers.pdf

I have used 1/2 teaspoon to about 2 gallons with no problems. I never noticed any real benefit to my plants but that's not to say there weren't any.

I think some plants will benefit and some won't. I know a number of growers who use it. I think some Chinese paphs would benefit from it at least.

Thanks for that Ray a very interesting read, I will have to read that a few times to really understand
it well !
Am I right in thinking that the urea nitrogen has to be broken down by bacterial and microbial action before the plants can take the nitrogen up
Regards
Des

Ray
The five articles by Dr Argo are some of the best guidelines around - Think everyone who fertilizes anything should read all five. It is a good sevice that you provide on your website. Antec also has a good
paper on the subject at Notes on Fertilizer use