How Long Do Worm Castings Last?

Worm castings are the most powerful soil supplement and plant growth booster you can find anywhere. If you buy a lot of castings at once, you might be worried that they’re going to spoil before you can use them.

Although this is a very common concern, if you follow a few simple guidelines, you’ll be able to keep those castings safe and functional for a long time. What do you need to do to preserve the effective life of your worm castings?

Don’t Get Them Wet!

The first rule of preserving worm castings is… don’t get them wet! Yes, that’s also the first rule of caring for Gremlins, but we promise we didn’t make this up. When you apply worm castings, the first thing you should do is apply water.

That’s because it activates the microbes in the castings and puts them to work doing their thing for your plants and soil. So, what would happen if you got the castings wet before you apply them? The microbes still become activated and go to work doing their microbe thing.

This means that if you get the castings wet, the microbes will begin doing what they do and before long, the microbes will die. When storing your castings, keep them in a completely dry location such as a garage or an out-building.

If possible, keep them in a resealable container such as a bag or a bin of some kind. If you can do this successfully, you’ve mastered the first step in preserving your worm castings for the long-term.

Keep Them Out of Direct Sunlight

Ok, we know this is another rule of raising Gremlins, but we promise we’re not just copying the Gremlin rules. If you put worm castings in direct sunlight for an extended period of time, the microbes will die. They don’t have to be in complete darkness while you’re storing them, but don’t leave them by a window where the sunlight can get in and do its damage.

If you keep them in the garage, basement, or an out-building, you should be good with this restriction as well. Just don’t leave them in a sealed up container or bag outside and think they’ll be alright.

Obviously this doesn’t apply when you use the castings in the garden, as they mix in with the soil and they have a food source.

How Long Can They Last?

So exactly how long will worm castings last if you follow these basic rules? While we’ve never actually been able to keep any in stock this long before, we’ve heard rumors of them lasting for two years or more and still working. How is this possible?

When you don’t use worm castings for an extended period, the microbes will go dormant. It’s kind of like they hibernate for the winter, just ready to wake up and start microbing again. When the microbes in the castings are dormant like this, as soon as you apply them and water them, they “wake up again” and start doing their thing.

This is true even if the castings have frozen in the winter. Some people keep them in containers in environments that are not climate controlled and they freeze in the winter. Even this will not ruin them.

The microbes can go dormant, freeze, and then be reactivated when they get wet later. We’re not exactly sure what the absolute upper limit is on how long you can keep worm castings. Just as a rule of thumb, we would recommend planning on about two years as the max.

Do the Worm Castings Math

When you’re trying to figure out how much to buy, it’s important to do the math on how fast you’ll go through it. Calculate approximately how much you’ll need with these rough guidelines. (link to guidelines)  Once you know that, figure out how long the growing season is for the plants that you’ll be growing.

You can apply worm castings as often as you like, without hurting the plants. The more often you apply, the better results you’re likely to have. However, the castings can usually last for about two months once they’re applied. So if you want to reapply every two months, factor that into how much you need.

For example, if your growing season is 5 months and you calculated that you need 200 pounds per application, you would buy 600 pounds for three applications. If you buy 2000 pounds, then you’ll have 1400 pounds left over for next growing season.

Overall, worm castings are pretty flexible and durable. If you’ll just follow some basic rules and treat them like Gremlins, you should be able to keep them for quite a while. Also, there’s not a rule about feeding them after midnight, so you don’t have to remember that one. 



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