How to keep granular MSU from mold?

[greenpassion]

Hi all. I use MSU granular fertilizer for my orchids. I don't keep it in the fridge because when I did last year, it became very lumpy. This time I had purchased those little silicon packets, and put 2 of them in the jar, and I've kept this jar on a shelf under where I grow my phals. Over the past few weeks, I've noticed the color changing from the brighter pink tone, to a dull peach. Then this morning I noticed that it looks almost like it's molding! I am at a loss as to what to do. Should I use more than 2 packets in the jar? Or go back to refrigeration? And, is it ok to continue to use this if it's turning color? Here in Vermont it's been rainy more than usual, and the humidity levels in my house hangs in the 70% range. Any ideas?

[estación seca]

The packets absorb a small amount of water, and then they cannot absorb any more. Your container is not air-tight, and your fertilizer is sucking up water from the atmosphere. I don't think the packets are a good solution in a humid climate. They don't suck up very much water, and are soon exhausted.

There are several options that might work.

The easiest is to dissolve all the fertilizer in water and make a stock solution. Then store that in your refrigerator. Note that if you make the stock solution very concentrated, the chemicals may precipitate out when you chill the solution.

Start with the typical amount of powdered fertilizer you would use when you mix up fertilizer. Figure out how many units of that measure the fertilizer represents. Then you will add water to get a final volume of some easy multiple of that.

For example, if you calculate you have enough fertilizer for 200 of your usual doses, you might want to add enough water to the powder so you wind up with 200 teaspoons of concentrate (or 200 tablespoons, or 200 half teaspoons, or whatever you want.) Then you would add one teaspoon of concentrate to your water instead of the amount of powder you normally add.

Note that you cannot just add 200 teaspoons of water to the powder and expect it to retain the same volume. Often when dissolving something in water the volume of the water increases. Add most of the water, dissolve, then measure how much you have. Add water to yield the final amount.

Some people dry out the fertilizer at very low heat in the oven as soon as it arrives. Then they divide it into smaller amounts and seal those in airtight containers. They open the smaller containers one by one.

[greenpassion]

Thank you for your reply, but in all truth that is far too complicated for me. Should I throw away what is there and buy a new jar and put it into an airtight container? Is what I have still usable? I could go for the liquid but that's pretty expensive.

---------- Post added at 04:53 PM ---------- Previous post was at 04:15 PM ----------

Oh! Just thought of something. What if I used a vacuum sealed container. Like a vacucraft container? It sucks all the air out for food or juice. ??

[estación seca]

You can use your existing fertilizer. It won't be damaged. It just might solidify into a lump. Fertilizer isn't that critical, so it won't be much different than using fresh.

Dry it in your oven if it's getting mushy. Use something to scrape powder off the lump and use it the regular way.

You will have to use heat to dry it, or send it someplace with extremely low humidity. The sealed containers prevent more humid air from entering but don't do anything about what's already there.

[greenpassion]

Ok. I really appreciate your help.

[Dollythehun]

I use the same product. I keep it in a zip lock bag I under the sink. It's gets lighter but not lumpy or moldy.

[greenpassion]

Hmm. Maybe I'll try the ziplock before I go out and buy an airtight container...

[Ray]

No mold is going to grow in that concentration of inorganic salts.

What you're seeing is changes in the blue indicator dye that's added so you can tell it is in solution.

If you want to avoid the problem altogether, make up any concentrated solution when it's fresh, and just use that to make up your final solution for application.

[greenpassion]

Good to know Ray! Thank you.

[Ray]

I should have expended a bit.

The dyes are sensitive to pH. In the dry powder, you cannot even tell they're there, but once in water, made acidic by the fertilizer, they turn blue. (Hint: if you dye your hands blue with it, ammonia will reverse the coloration.)

In the jar, if left open enough to absorb moisture, you get a "localized dissolution" of some other components that gives it that strange reaction that looks so bad. It is only appearance, and actually doesn't seem to affect the nutrient value.