Methods for Supplementing Magnesium Long Term?

[rives]

I grow in a mix of SS#4 and perlite, using Blumats for watering. My water is very low in calcium and magnesium (4.6 and 1.1 ppm, respectively). Gypsum has helped boost the calcium levels, but I am having trouble supplementing the magnesium to sufficient levels, which is amplified by the fact that I seem to grow mag hogs and use LED's for a light source.

My reservoir is self-topping and utilizes an automatic circuit to periodically bleed off the supply loop in order to purge air bubbles. This, along with the build-up issues with Blumats, keeps Cal-Mag from being a good option. I am out of town roughly 10 days a month, so the Cal-Mag gets diluted down to ineffective levels very quickly.

I add epsom salts to my soil mix when re-potting, but this addition seems to be very short-lived. I have started putting a small "mound" of epsom salts beneath the Blumat dripper, and this has helped, but I am concerned about both adding too much and the high levels of sulfur that is contained in all of the calcium and magnesium supplements. Dolomitic lime would be a good source of both calcium and magnesium, but my pH is just right without it, and when added it raises the pH above optimum. Straight dolomite, without the limestone, seems like it would be perfect, but I haven't been able to find it.

Anyone have some suggestions? Thanks.

 

[wilbur]

as I understand it, it's not possible to have dolomite without the lime ... or it wouldn't be 'dolomite'.

dunno about sulphur buildup, have never done this ... but epsom salts can be applied by foliar spraying.

 

[rives]

as I understand it, it's not possible to have dolomite without the lime ... or it wouldn't be 'dolomite'.

dunno about sulphur buildup, have never done this ... but epsom salts can be applied by foliar spraying.

Very possible that they only occur together. I've seen information sources that refer to "dolomite" and "dolomitic limestone" as if they are separate entities, and dietary dolomite supplements only list calcium, magnesium, and iron as ingredients. Perhaps any other ingredients are being isolated and removed somehow.

I've been doing foliar sprays with epsom, but I don't want to do foliar feeding during flowering.

 

[WeedNNoodles]

i would try getting some of those dietary suppliments and let them break down in a gallon of water and then use a sprayer to foliar feed the mixture to a few plants to see if it helps.

 

[joe fresh]

http://www.extremelygreen.com/Product.cfm?Name=Sul-Po-Mag

 

[PoopyTeaBags]

epson salts?

 

[analogue]

Rives, one of the things I use in my recipes is magnesium nitrate.

 

[shmalphy]

epson salts?

epsom salts

 

[PoopyTeaBags]

epsom salts

wow thats very clever how ever me googling epsom salts does nothing to help rives... as i was just asking if hes tried it... if your going to be a smart ass please do it when its appropriate... thanks...

however i must of missed hes already tried that so it was at least a useless post alltogether...

 

[rives]

Rives, one of the things I use in my recipes is magnesium nitrate.

I found Magnisal (magnesium nitrate) in my poking around. The thing that concerned me with it was the high level of nitrogen - it has 9.6% magnesium, but also carries 11% nitrogen. Magnesium sulfate (epsom salts) is 9.8% magnesium and 12.9% sulfur. I am pretty happy overall with my nutrients and have concerns about boosting the levels of either nitrogen or sulfur to that extent. To get where I need to be with the magnesium, it would damn near double the existing nitrogen or quadruple the sulfur.

Also, I don't know how well magnesium nitrate hangs in the soil, but the epsom salts seems to go away very quickly. I was hoping to find a slow-release source that could be combined into my mix initially and last throughout the grow, but haven't found anything that looks promising.

 

[Budley Doright]

Actually you have found something promising but for whatever reason dont want to try it....


dolomitic lime is the answer.....


I believe you should try it and not just assume it wont work....because of some ideas you have about ph.....


Epsoms is in fact very water soluble as you have discovered....it will quickly leach from the soil....


Most limestone isnt dolomitic its calcitic...


what makes dolomite dolomite is that it has at least 6 percent magnesium....


If you really believe that you ph is perfect....


add straight peat....low ph....


and then add dolomitic lime....

 

[shmalphy]

wow thats very clever how ever me googling epsom salts does nothing to help rives... as i was just asking if hes tried it... if your going to be a smart ass please do it when its appropriate... thanks...

however i must of missed hes already tried that so it was at least a useless post alltogether...

Based on the fact that the OP had mentioned them, and since you misspelled Epsom, I assumed maybe you had never heard of them before.

 

[shmalphy]

Also, try glacial rock dust or Azomite for remineralization.

Here's 50lbs for $25
http://www.groworganic.com/gaia-green-glacial-rock-dust-50-lb.html

 

[YosemiteSam]

Are you feeding anything except water? Can I ask what your pH is and how you measure it? Have you ever had your soil tested for base saturation...tells you what is on your cation exchange sites, you should be around 65% Ca and 15% Mg.

If you are happy with everything else I would find a soil with a lower pH that would allow you to use some dolomite.

 

[Nondual]

http://www.extremelygreen.com/Product.cfm?Name=Sul-Po-Mag

Yeah that and YoesmiteSam dropping the knowledge again...

Have you ever had your soil tested for base saturation...tells you what is on your cation exchange sites, you should be around 65% Ca and 15% Mg.

Not many peeps test their soil for base saturation.

 

[rives]

Actually you have found something promising but for whatever reason dont want to try it....

dolomitic lime is the answer.....

I believe you should try it and not just assume it wont work....because of some ideas you have about ph.....

If you really believe that you ph is perfect....

add straight peat....low ph....

and then add dolomitic lime....

Burnt Rope - I was speaking from experience, not from anticipating the results. My runoff pH's at 6.3-6.5, and the last time that I added dolomitic lime, it went to 7.1. The d.l. was added at the rate recommended in Vic's, Sub-Cool's, etc recipes.

Straight peat was the treatment that I used at that time, which worked, but it was a lot of experimenting around to get where I needed to be and top-dressing doesn't work particularly well with the single moisture point from the Blumats. This may wind up being the best answer, though, since I'm unable to find a magnesium source that isn't high in other minerals.

Schmalphy - thanks for the tip on the Azomite and the glacial rock dust.

 

[rives]

Are you feeding anything except water? Can I ask what your pH is and how you measure it? Have you ever had your soil tested for base saturation...tells you what is on your cation exchange sites, you should be around 65% Ca and 15% Mg.

If you are happy with everything else I would find a soil with a lower pH that would allow you to use some dolomite.

I use Osmocote Plus as a fertilizer - I know, I know! It works well for the periods of absence that I have and the Blumats, and my usage of a just-add-water soil mix resulted in it running out of steam about the 3rd week of flowering. I would like to get back to it at some point, but I don't have the time at this point to work it out.

I test the run-off by bringing the soil to saturation and letting it sit for an hour, then adding enough extra to get roughly an ounce of run-off. This sample is then tested with a BlueLab pH meter.

No, I've never tested for base saturation. Changing out the soil is certainly an option.

 

[shmalphy]

I would go with EWC, bat guanos, and kelp instead of the houseplant food. You will thank me in 3 months when you taste what I am talking about.

 

[YosemiteSam]

One more thought. You could change your calcium source to a lower SO4 source. That way you could merely mix the epsom into your fertigation water and get better (more even) results than top dressing with it. edit...generally epsom adds 25 ppm Mg and 33 ppm S when you add 1 gram to 1 gallon of water...so you can sort of use that as a guideline for additions.

Here is one possibility...check out the Humical at the bottom of the page http://www.midwesternbioag.com/calcium-products.php. It will keep your pH similar to gypsum but provide less S.

An even better source would be something called Ixper 70 from Solvay Chemicals. It is Calcium Peroxide. And it works really, really well. I am testing it in coco where I do not want pH to rise. The problem is that it is considered a very potent oxidizing agent that may not be sold to the general public...I got a sample, fell in love with it, and now can't find a source...DOH

edit...that is an excellent way to check pH...much more accurate than most people use.

 

[joe fresh]

hey rives here is a lil trick i use....i add enough dolo lime to adjust ph to 6.5-7....then when i water i adjust the water ph to 6.0-6.2....so when i water the plat will be recieving at 6.0...then over the course of a few days as the pot dries the ph will rise back up...making for full absorbtion of nutes in full range of ph....but over time(like a month and a half to 2 months the ph will settle back down to 6.2-6.5 depending where the water ph was being set....


at the begining of this run i added lime...(dec 18)...then vegged for 3-4 weeks and transplanted and mixed in more lime...then i continued watering at 6.1ph and now am on day 28 of 12/12 and runoff ph is 6.2....so now i raise my water ph to 6.5-6.8 so it adjusts accordingly...


dolomite lime will never raise the ph above 7 because the ph of dolo lime is 7.... the problem of adding too much dolo lime is not the ph factor, but rather the fact of adding too much calcium will throw off the other nutes in the mix...