Toni,
I had wondered that same question before and did some reading on the subject. From what I have read, they don't go bad, that's ANY kind of fertilizer, liquid, powder, or timed release.
I did throw away a small bag of some of the blue soluable stuff last year because it became kinda wet from me sticking my just washed hand in the bag, it was literally a melted mess, but, it was probably still good.

Billy Rae

I found this online...

"With liquid fertilizers, there might be some crystallization over time. The solubility of fertilizer salts increases with increasing temperature, so heating a container of liquid fertilizer (by putting it in a pot of hot water) should dissolve any crystals.

Otherwise, nitrogen fertilizers can degrade through loss of ammonia (a gaseous nitrogen compound) to the atmosphere. The ammonium compounds which are used as nitrogen carriers break down very slowly unless mixed with alkaline substances, but they may lose some weight and value over prolonged storage ... especially if their container is not well sealed.

Some organic fertilizers can become moldy. Their nutrients may blow away as spores."

Hope this helps!
Chandres

I saw that same thing (above) about degrading of fertilizer, but everywhere else the articles would say it doesn't, so who's to say for sure???
Nothing last forever and I'm sure there is some "degrading" over time, but how much degrading would be too much? I guess your plants would tell you.
I have plenty of old fertilzer around here and they still seem to be doing an ok job of it.

Billy Rae

Oh My God, my thread reappeared..that IS spooky..lol
I wonder if the thread regarding Colocasia mysteriously returned..have to check it out..LOL..strange.

Billy, I know what you mean about powdered fertilizer..I opened the plastic bag it comes in, (for acidic plants) and found dark blue speckles..perhaps it got wet during handling, so don't want to chance it..Afterall, if you or anyone here read up on fertilizers, they say never use mixed fertilzer that's been sitting in water more than 8 hours..or less..
I tossed it, so don't have to worry..We went to Ace Hardware, purchased new ferts..
I don't know if old fert would harm a plant, but at the least, may lose nutrients.. It takes 2-3 days to fertilize my plants..why waste time using something that's not going to work?? Or worse, harm/kill plants?

Chan, your post is interesting..I agree. Most of my ferts are powder though..The only liquid ferts I've seen are those by, I believe, Shultz..the directions say, use 7 drops per gallon of water, 'everytime' you water..sounds like they're trying to push their product, instrucing people to use every watering. Wouldnt you think??? Toni

I have first hand bad experience from expired fertilizer(s). We purchased a 3 part liquid nutrients namely general hydroponics. Began having problems for 5 months, then bought a new batch, saved the old , after realizing it was over 2 years old ( the green) GRO . The micro and bloom were 4 years old. The gro crystallized very quickly in the measuring glass, say in about 1 hour after leaving the residue sit on the counter. So I put the same residue of brand new Gro in another glass, and it did not crystallize.

Here is our results : the plants continuously formed claw like leaves! I have never encountered this until using expired fertilizers. The products were never frozen, at least not in my possession. imagine the losses! 6 gallons of lost production! 6 months of wasted time !

I recommend not using expired fertilizers if you expect a return on your investment. This is a considerable loss. Greatly disappointed.