Old plant food - does it expire?

[RainCloude]

I've had a clear out of the shed and I've found old boxes of miracle grow, nitrogen feed and sulphate of iron. They are frozen hard with the cold! No idea when I bought them.

Does anyone know whether these things lose their potency over time, or can I use them still as if I'd just bought them?

I think this was asked on gardener's question time once and nobody was that sure but the general consensus seemed to be probably not.

Anything that should be dry crystals will eventually take on water and clump together though, which could prevent you from dosing it correctly

Sorry ambiguous! It probably doesn't expire

I don't think it does expire. I've used stuff that's decades old. If the plants don't respond to the plant food, then it's probs not any good but it won't do them any harm.

Thank you ....
All of the stuff I have is meant to be dissolved in water anyway so the fact that it's clumped together doesn't matter.
I will use it I think!

I can generally see the correct dose of miracle grow by looking at the colour - that's how I do it anyway. Nothing too exact in my world!

It depends whether the constituent chemicals are stable. Ferrous sulphate (sulphate of iron) is pretty stable, I had it in my chemistry set when I was a child.

I'd agree that they'll be fine, so long as you can work out the dosage.

But - if they are powders to be dissolved, they're not solid because they're frozen, but because they'll have taken on moisture and then coagulated into a solid lump - they won't revert to powder when warmer. You could break bits off the lump, or dissolve the whole thing in water?

Intending to slice chunks off and judge dosage from colour of the water when diluted. Or I could bash the solid mass with a hammer (it's in a plastic bag).
Happy to know the beneficial properties should still be present, thank you to all who posted 😊