At Worms Downunder, we’re proud and confident in our worm cast liquid concentrate —a living, breathing product designed to boost mineralisation through the power of beneficial microbes. Lately, we’ve been exploring ways to enhance it's nutrient content, including the idea of dosing it with urea to add nitrogen. But here’s the thing: our brew isn’t a fertiliser, and we’re not chasing high NPK (nitrogen, phosphorus, potassium) values. Worm Brew is a tool to be used alongside your nutrient applications. Our focus is on the microbes—and science backs why that matters.
The Urea Experiment: What We Learned
We’ve run trials adding urea—a nitrogen-rich compound—to our Worm Brew, wanting to explore increasing nutrient levels. After all, nitrogen is a key nutrient for microbial growth and plant growth. But in every test, we hit a wall: the brew doesn’t stay stable. After just 3 days in a container, you open it, and bam—an ammonia stench hits you in the face. Why? Let’s break it down.
Urea (CO(NH₂)₂) breaks down fast in the presence of urease-producing microbes (common in worm casts). It turns into ammonia (NH₃) and carbon dioxide (CO₂).
In water, some ammonia becomes ammonium (NH₄⁺), but at the slightly alkaline pH of worm casts, a lot stays as NH₃ gas. Early on, our aerobic microbes—like Bacillus and Pseudomonas—feast on this nitrogen, multiplying like crazy. That’s great, right? Not quite. This population boom draws down dissolved oxygen (DO) fast. Without active aeration, the oxygen vanishes, and the party slows down. The microbes can’t keep up with the ammonia, and it builds up—off-gassing as that pungent NH₃ we smelled after just days of storage.
The Science: Microbes vs. Stability
Science tells us this is predictable, aerobic microbes need oxygen to thrive. Add a nitrogen source like urea, and their growth explodes—until the DO runs out. Then, the system shifts. Aerobic activity stalls, and if anaerobic microbes kick in, you might get nitrogen gases like N₂ or N₂O. But in our case, it’s mostly unconsumed ammonia piling up. High NH₃ levels can even become toxic to the microbes, killing off populations and leaving the brew unstable. That’s why, in all our trials, dosing with urea didn’t create a stable, nutrient-rich product—it created what smelt like a gas bomb.
Competitors’ High NPK values: How Do They Do It?
Some competitors boast high NPK values in their microbial products, indicating they’ve cracked the code. We’re curious—and here’s why. If they’re adding nitrogen (like urea) to a living microbial brew, science suggests they’d face the same issues we did: microbial overgrowth, oxygen depletion, and off-gassing. We can’t say for sure without testing their products and understanding their methods, but we can say that our Worm Brew, a diversely, aerobic microbial brew, doesn’t play nice with excess nitrogen long-term in a bottle. The microbes consume it, multiply, and upset the balance—leaving you with off-gassing, not a stable all-in-one solution.
Our Priority: Microbial Life Over an All-in-One Bottle
Our Worm Brew isn’t about packing nutrients into a bottle—it’s about delivering living microbes to your soil. Worm casts are already a microbial goldmine, teeming with beneficial organisms that improve soil structure, cycle nutrients, and fight pathogens. Adding urea might sound like a way to turn it into a fertiliser-microbe combo, but our trials show it destabilises the microbial population we’re worked hard to establish. That’s why we don’t bottle it as an all-in-one product.
Instead, we recommend pairing lower rates of your fertiliser—like urea or other nutrients—with our Worm Brew at application. Fertilisers are brilliant when applied at lower rates alongside microbes. In the soil, you get the microbial population boom you want, fuelled by the added nutrition. This drives benefits like mineralisation, where microbes convert organic matter and nutrients into plant-available forms. It’s a perfect synergy—happening right in the soil, where oxygen is plentiful and the system can breathe. You get all the conversion we’re after, without trying to bottle it together.
We’re not here to knock fertilisers—they’re a key part of farming when used smartly. We just can’t make them work in a stable, bottled mix with our live microbes. Some competitors lean on high NPK as a selling point, but we’re focused on what Worm Brew does best—supporting soil ecosystems with living aerobic organisms.
What’s Next?
We’re still experimenting—maybe a tiny urea dose with active aeration could balance microbial growth and stability in the brew itself - we'll keep you updated. For now, we’re not trying to bottle an all-in-one fertiliser. Pair your Worm Brew with nutrition at application, and let the soil be the stage for those microbes. Next time you crack open one of our containers, you’ll smell earthy, sweet microbes.
Have thoughts or questions? Drop us a line—we’d love to hear from you!