You open a bag or container of fertilizer in the spring and you’re in for a shock: it’s as hard as a rock! It can’t be still good … but in fact, it is.
You may not have noticed, but there is no expiry date on most fertilizers. That’s because they’re made of minerals and the minerals don’t decompose … well, not over a normal human lifespan, at least. So, to turn your lump of fertilizer into something useable again, just crush it up with a hammer or some sort of pestle (a piece of wood, for example). It’s then good to go again.
Theoretically, liquid organic fertilizers could decompose and some manufacturers include do an expiry date: quite a long one, usually 8 to 10 years. In fact, though, if they decompose, they still only become simpler minerals that plants can use … and therefore, they remain useful.
Even so, some liquid fertilizers can settle over time and form deposits on the bottom or the sides of their container. If so, just shake them thoroughly to remix the deposits with the liquid.
Weed and Feeds
The exception to the rule that there is no expiry date on fertilizers is “weed and feed” type fertilizer, that is, one that combines fertilizer and herbicide in the same product. Usually, these products have an expiry date of 3 or 4 years, but it’s the herbicide that loses its effectiveness, not the fertilizer.
Note that weed and feed products containing synthetic herbicides have been banned in most countries other than the United States. Only fertilizers that contain organic herbicides, usually corn gluten, remain on the market in Canada, Australia, and most of Europe. There is no expiry date on these. Just reduce these “organic weed and feeds” to powder if ever they harden.
Keeping Dry Fertilizers Dray
If dry fertilizers harden, it’s because they’ve come into contact with moisture. You can usually keep them dry and in top shape by storing them indoors in a dry spot over the winter.
Fertilizers left outdoors, in a tool shed, for example, can easily be affected by condensation as temperatures drop. To prevent this, attach a pack or two of silica gel to the inside of the container to absorb excess moisture.
Fertilizers: even if their structure changes, you can still use them, right to the very last molecule!