Can Liquid Fertilizer go bad?

[ruthann]

I have a liquid fertilizer for orchids...it is going on 2 yrs. old. Can it go bad due to age? Is there a rule of thumb to follow how long to keep it? Thanks

[Ray]

If it's an organic fertilizer, yes it can degrade. Most fertilizers tend to be mineral-based, so unless you let the water evaporate, it's no issue.

Sometimes the less-soluble minerals will precipitate over time, especially if the stuff is stored cold, so shake very well before dispensing it. or if you really want to be crafty:

1. Weigh the bottle and its contents.
2. Pour the fertilizer into a larger container, then weigh the old, empty one to determine the weight of the fertilizer solution only.
3. Measure out that same weight of hot water and mix it with the old solution.

At that point the precipitated stuff should redissolve, but you now have a solution that is approximately half as strong, so double your dosage.

[ruthann]

Thanks for info, Ray.

[Magnus A]

One other potential problem can occur!
If your fertilizer contains metals ligated to EDTA or some other compexation agent it could have been oxidized by air. The metals could then be in a physical state impossibly for the plants to take up.
Fe2+ EDTA complex could brake down to Fe3+ that will be Fe2O3 = rust. I would also stretch this to say that the oxidation products from EDTA could also be potential armful.....

/Magnus

I have heard reports of solid MSU stored open to air and not dry that turned brown and got a smell of ammonia. Most likely there is a iron amine complex that has been oxidized to rust in these cases.

[Ray]

Good point about the EDTA used to chelate the iron, but it's a pretty stable chemical, so unless you store it warm and exposed to light, not much should happen.

Some one at Clemson did a study on that, and showed that dark storage = no degradation, while when exposed to 3500 fc of light, 90% of the FE-EDTA degraded in 10 days. Doubling the light intensity doubled the rate, as did increasing the temperature from 68°F to 104°.


I have not heard that about the MSU formulas, but have two comments:

1) The minerals used in them are not unique, so the same could be the case with others.

2) Why would anyone store any fertilizer powder open to the air?

[Magnus A]

Ray

I agree partly with your comment. If stored dry FeEDTA is quite stable but some moisture and oxygen from the air is a bad combination, together with warm enviroment and light disaster will happen after some time. Leave iron in air with som moisture and you will get rust but that everyone knows I hope.

For point 2) I think MSU and some other fertilizer powder have been sold in small ziplock? plastic bags, at least in Sweden. People seems to store them without closing the bag correctly. Why ? have no idée but I think the lack of knowledge is a factor.....

/Magnus

[Pseudo-Scientist]

This is my first post!!!
For hydroponics, if you store your fertilizer in the dark and at room temperature (like the bottle says), it should be fine. For soluble mixes (crystals that need to be mixed wit water), even more so.

I've been using some stuff thats over a year old (Dutch Man liquid), and all I've noticed is some crystalization on the lid, which I attribute to oxygenation.

Definitely not for organics. I used old organic stuff without checking....boy did I nearly kill some houseplants. Like watering with mold.