11 Disadvantages of Worm Castings to Be Aware Of

Talk to anybody who’s been gardening for a while, and eventually the subject of vermicomposting will probably come up.

a healthy group of red wriggler worms from the bait shop
a healthy group of red wriggler worms from the bait shop

Vermicompost, also known as worm castings, is literally nothing more than worm excrement mixed in with soil, and it has plenty of people singing its praises lately.

That’s with good reason, because this stuff really does work as all-natural fertilizer around your garden and around your home.

But, like anything that’s being praised too much, worm castings are not without drawbacks even though the most enthusiastic users of the stuff try to pretend otherwise.

I’m not here to turn you away from worm castings, but I do want to save you from some disappointments and mishaps that I have experienced myself.

I’ll do that by telling you about 11 disadvantages you must prepare for and plan around.

With these insights, you can put worm castings to the best possible use for your plantings. Grab your gloves and let’s get going.

1. Production is Usually Space-Inefficient

One of the single biggest problems with worm castings, assuming you’re making your own, is it just isn’t space-efficient.

Even a sizable bin or stack that is devoted to producing worm castings, if the worms are happy and healthy, will only produce a small amount over the course of a year (a few shovelfuls at most).

Starting from zero you’re going to spend at least 6 months waiting until you got a quantity that’s even worth using.

This leaves you with a couple of options if you’re making your own…

You either wait and wait and wait, planning ahead a year or more, until you’ve got a suitable quantity for fertilizing or amending your soil.

Second option is to go all in and add more bins or stacks to increase yield. This is definitely viable, but hardly efficient, and compared to a traditional compost pil,e your worm casting production line is going to take up a lot more space and produce a lot less usable material.

For some folks, this alone is a deal breaker depending on how much room you have or how much you want to devote to the process.

2. Your Worms Need Consistently Good Conditions

Everything in gardening is seasonally dependent. We know that, but when it comes to making worm castings, it is even more dependent on the seasons, the weather, and the climate.

Generally speaking, when winter rolls around, your worms are done for unless you’ve taken pains to keep them in a climate-controlled environment.

If your worms get too dry or too moist, they’ll be in trouble. They might stop eating, they might migrate to a different section of the bin, reproduction can be disrupted- lots can go wrong! If worms get too hot or too cold, they will perish, or if they’re outside of their ideal temperature band, they can decide to take their chances somewhere else.

This means that, depending on your setup, your worms might escape!

You’re going to be treating your precious little casting creators as pets or livestock much more than you would when it comes to the management of a traditional compost bin.

You must always check on their overall condition regularly, and still do that without unduly disturbing them which will also cause slowdowns or problems. I’ll talk more about that a little later…

3. Worm Bins Need Lots of Care

Aside from the worms, the bins themselves will need a lot of maintenance, both to keep the worms happy and healthy but also to improve the quality and safety of your collected vermicompost.

Worm bins, more than most other types of compost bins, are notorious for filling up with water from rain or even condensation.

Because, generally, you cannot leave wide open gaps and holes on the sides and bottom of your bins because the worms could just crawl out and either die or escape.

This means it will be a constant battle to maintain the correct moisture levels, and one of the first things you must do when it starts to rain is either cover or move your bins so they don’t fill all the way up and wash out.

4. Worm Bins are Vulnerable to Pests

Your worm bins will probably prove to be highly vulnerable to pests and predators. I’ve never seen a traditional compost bin, except perhaps for the most radically mismanaged, attract flies, gnats and other insects like a worm bin does.

Some of these creatures are just going to be pesky for you, but others can be highly problematic for your operation.

Creatures like ants can deliberately target your worms and kill them, chopping them up and carrying them away as food.

Perhaps most worryingly are larger mammals that actually eat worms, with raccoons and possums being foremost among them.

Not only will they dig through your soil to find the them and pluck them out, they’ll make such a mess of the bin you’re going to lose a lot of that “black gold” you’ve worked so hard to produce.

Of course, properly protecting these bins from these pests is easier said than done. You generally want to keep your containers outside and away from your home because they don’t smell very good and they also need exposure to oxygen and light.

This makes them more vulnerable to mammals, and you still can’t just go off and use insecticides to repel smaller pests: that might hurt the worms, too.

This issue is a constant battle, in my experience…

5. Harvesting Castings Disturbs Worms

Probably the single most aggravating thing about vermicomposting is that even attempting to collect the castings from your bins, unless done with maximum caution and previous planning, is going to disturb your worms and slow them down, and you can potentially impact their reproductive performance.

Tipping, scraping, sifting, scooping and all of the other common methods for getting to that rich compost is going to stress your worms and potentially kill them.

It’ll take them some time to get back in the swing of things if they recover, and even if you are as gentle and as surgical as you can be you are likely going to disrupt and destroy their eggs which means fewer worms in future generations and reduced performance over time.

There is no great way to go about this, and pretty much all methods are somewhat traumatic for these tiny critters.

Best method I’ve found is the vertical approach, whereby you encourage worms to migrate to upper containers in especially designed, stackable, modular units.

This allows you to remove the lower one where the good stuff is, and collect it without rooting through the soil. It still might not help with the loss of eggs, but it’s better than nothing.

6. Worm Castings are Not a Complete Fertilizer for Needy Plants

One of the last things that the worm casting champions will tell you is that vermicompost is simply not a complete fertilizer. It’s especially lacking for the hungriest plants, typically fruit trees.

This is hardly controversial, it is just the facts, but if you’re making the stuff with the intention of supercharging those hungry and hard-to-please plants in your garden, you’re going to be let down.

I can tell you right now that even the richest worm castings are almost completely unsuitable for growing plants in by themselves.

Generally, you’ll rarely encounter worm castings that have an NPK rating higher than 5-3-3, and most of it is significantly less than that.

Sure, this is easily fixed by mixing in supplements, amendments, and other nutrients to the vermicompost itself, or using it as an ingredient in your own sort of super fertilizer.

But, if you’re going to go to all that trouble, why not just mix up a rich and highly nutritious fertilizer using those same components in the first place and save yourself the trouble?

7. Leachate Runoff Can Contaminate Castings and Soil

One of the single biggest misconceptions, and potentially the most harmful, associated with vermicomposting is the ignorant use of leachate directly from the bins themselves.

This disgusting liquid runoff is commonly mistaken for “worm tea,” something we’ll talk about in a minute, but the short version is that worm tea and leachate are two completely different things.

Whereas worm tea is liquid fertilizer made from the actual worm castings themselves, the leachate is a hideous bacteria-ridden slurry that can contaminate your actual fertilizer and potentially turn your produce toxic if you use it as you would worm tea.

This stuff needs to be drained off from your compost bin for the health of your worms, and then disposed of, not kept and used as fertilizer.

If you put it on fruits and veggies, chances are good that you and your family are going to get sick if you eat them.

At the very best, and assuming it doesn’t smell foul, you can water this stuff way down and then use it to water any plants that you won’t eat and don’t have much contact with, but I don’t even recommend that.

Consider the stuff hazardous waste that is a byproduct of the worm casting process: handle it cautiously and get rid of it, especially if it stinks to high heaven.

8. Not Great for Wide Area Fertilization

Compared to other high-value NPK fertilizers, worm castings are especially poor for a wide area fertilization of the kind typically done prior to a mass planting.

You simply aren’t going to have enough of the stuff, and if you do, it probably isn’t going to deliver enough nutrients to get your new plantings off to a good start.

By comparison, regular compost and even bagged fertilizers are far better and likely to be far cheaper when it comes to your cost-benefit analysis.

9. Inefficient as Soil Amendment

Worm castings are pretty decent as a soil amendment in the grand scheme of things, but once again, they’re simply inefficient because you probably aren’t going to have enough of it to make it worthwhile unless you are working in a very small area or a dedicated planter like a raised bed.

By all means, if you have enough for your purposes, definitely use it, but remember that it is expensive and time-consuming for what it does.

If you know you need to amend the soil over a larger patch of ground, or you have many planters, you probably won’t have enough worm castings to do a good job of it.

For smaller pots and planters, though, or if you have been stockpiling the stuff, it does work fine.

10. Making the Most of Vermicompost Means Making Worm Tea- An Extra Step

Maximizing your return on investment when it comes to your worm castings means you’ve got to make worm tea with it.

Worm tea is basically compost tea made with worm castings instead, and it really is great for house plants, fruits, vegetables, and more.

It even has more nutrients to offer because you’re going to add molasses to it to encourage the growth of beneficial microorganisms.

It’s not hard to make, but you do need to let it steep for about a day, and the collection and setup process is yet another time-consuming step in what has already been a lengthy and time-consuming affair.

Is it worth doing? Sure, but I don’t know that I like messing with it after I’ve already gone through months of drudgery to keep these worms alive and working.

11. Expensive to Buy Over the Counter

By now, some of you have already decided that you want the benefits of worm castings, but you’re unwilling to go through all the heartache and hassle associated with making it yourself.

You are in luck, because it’s entirely possible to just buy worm castings, prepackaged, and over-the-counter, just like you would any other fertilizer or soil amendment.

But the bad news is that worm castings are still expensive. Too expensive as far as I’m concerned!

It is hardly uncommon to pay two or three times as much for a small bag of worm castings than you would for a comparable bag of major brand synthetic fertilizer.

Basically, you’ll be paying a premium for organic, all-natural fertilizer that is “underpowered” when it comes to giving your plans the nutrients they need…

What’s worse, worm castings take significantly longer to release what nutrients they have into the soil, so you cannot purchase and then put this stuff down to give your plants a shot of nutrition that they might desperately need.

Unless you’re determined to stay all organic with fertilizers and additives in your garden and elsewhere, the stuff probably isn’t worth the expense.

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