At work last year, one of my colleagues decided to grow a tonne of chili plants.
He promised to distribute some of these chilis amongst the rest of us. I’d requested Jalapenos, as this breed was missing from my own collection this year.
When they came, the chili plants were poor specimens indeed. Each one was pale and sported just a handful of leaves, while the ones in my own propagators were several times the size.
When I investigated, I suspected the cause was the compost – a thin brown material that dried and caked out hard without constant attention. (When I checked with my colleague, he told me this was supposed to be specialized chilli compost.)
After helping the plants recover with simple potting compost and a spell in my propogator, I decided to experiment.
I put one plant in regular compost, one in rough home made compost, and one in a mixture of regular compost and worm castings.
All the plants did well, but the mixture of regular compost and worm compost performed best.
But the best result was another chilli plant I rescued after it was abandoned on a colleagues desk.
After potting it on in a mixture of home made and worm compost, the plant grew so huge we started comparing it to the blood sucking plant Audrey II in the Little Shop of Horrors.
The evidence for the benefits of worm castings
My little experiment was fun, but not big enough to prove anything scientifically. Fortunately, research carried out by the University of Maine found a host of benefits for worm compost:
- Nutrient Rich: Worm castings are packed with essential nutrients like nitrogen, phosphorus, and potassium that plants need to grow strong and healthy.
- Steady Nutrient Release: Castings release nutrients gradually, so plants can absorb them over time without overwhelming the soil.
- Gentle on Plants: Unlike some composts or fertilizers, worm castings don’t cause salinity stress, making them safer for sensitive plants.
- Boosts Plant Growth: Plants grown with worm castings grow larger and healthier compared to those using synthetic fertilizers or regular compost.
- Supports Soil Health: Worm castings help soil microbes thrive, improving overall soil quality and fertility.
- Balanced Nutrients: Castings provide a stable mix of nutrients without sudden changes, keeping plants and soil happy.
- Eco-Friendly: Worm castings are a natural alternative to synthetic fertilizers, reducing the risk of chemical buildup in your garden.
How to use worm castings wisely
Since my success with chilis and reading this research, I’ve become even keener on using worm castings.
However, although I do have a three-tier home-made worm bin, the quantities I produce are small in comparison to my three bin pallet system. That means it makes sense to use it with the plants that will benefit the most.
Use with pot plants (or plants started in pots)
If you’re like me, and you have a large garden, I’d suggest prioritising use of worm castings in pots. That’s because the amount of worm castings you can produce or buy simply won’t be enough to make a difference in your veg plot.
To illustrate, I took a large trailer load of manure this spring and composted it down, and it still wasn’t enough to mulch all my garden. To produce that amount of worm compost would be impossible for the home gardener, and buying it would be prohibitive.
On the plus side, if you do have access to a reliable, herbicide-free source of manure, you can rest assured that worms will do at least some of the work – they love manure and are naturally attracted to it.
Use when speed is a priority
With some plants, it’s not worth worrying about speed. For example, my kaffir lime plant has been slowly but steadily growing for the last 12 years, and is already far bigger than we need for both our culinary requirements and for those of our friends.
On the other hand, other plants are a race against time. Sweet peppers are a great example, as in my climate the fruit always seem to turn red just around the time the cold sets in. Tomatoes, chilis and aubergines are another example, because unless you are lucky enough to live in a warm environment the harvesting season never seems long enough.
With these plants, I think it’s worth giving them the extra boost they can gain from worm compost. I suggest using worm compost when they’ve already gained some size but are not yet ready to put in beds.
Use with hungry plants
Plenty of plants do just fine without the extra boost from worm castings. Plants like lettuce, pak choi, parsley and coriander always seem to do just fine, even when planted in reused compost. For that reason, I use worm castings with hungry plants that are more likely to benefit from that steady release of nutrients.
Don’t use with seedlings
I’d suggest avoid using worm castings with young seedlings. Worm compost is very nutritious, but the nitrogen levels may be too high for young seedlings, causing them to ‘burn’.
Mix with regular compost
There’s no need to use pure worm castings – I’ve had excellent results by mixing worm castings with regular potting compost, which can make your worm compost go a lot further.
Conclusion
If you’re a keen gardener, want to speed up growth or get that kick out of growing bigger, better vegetables, worm castings might be worth a try.
You can buy worm castings easily enough, or even better make your own castings with a home made or commercially bought vermicomposting system.
Just one word of advice based on my own experience. Before showing off your results in the office, be aware that it can result in more requests for your home made worm compost than you can possibly meet!
FAQs
What are worm castings?
In a word – worm poo. Before you get disgusted, know that these castings are rich in the nutrients that plants love such as nitrogen, phosphorus, and potassium.
How do I use worm castings in my garden?
You can dig it into the ground or mulch around the base of plants. However, because worm castings are normally available in limited amounts, I suggest prioritising their use in pots or for hungry plants where speed is a priority.
Can I use worm castings on all plants?
Worm castings are great for most plants, but they’re particularly beneficial for fast-growing or nutrient-hungry plants like tomatoes, chillies, and peppers. However, avoid using pure worm castings with seedlings, as the high nutrient content might cause burning.
Can I buy worm castings, or do I have to make them?
Worm castings are available at garden centers or online. It’s also a great idea to make your own – once you have a wormery set up, it really doesn’t take much work to manage it. You can use either a commercially purchased worm bin or easily make your own – check out our DIY guide for tips.
Are worm castings better than regular compost?
Both worm castings and regular compost are great for plants and soil. However, research suggests that worm castings may offer some unique benefits, such as a more balanced nutrient release and reduced risk of salinity stress. My own experiments with chilli plants also suggest they seem to lead to stronger, bigger plants. That said, worm compost is best used to complement rather than replace compost, as it is not usually feasible to obtain large amounts of worm compost.
Sources
Chaoui, H. I., Zibilske, L. M., & Ohno, T. (2003). Effects of earthworm casts and compost on soil microbial activity and plant nutrient availability. Soil Biology and Biochemistry, 35(2), 295-302. https://doi.org/10.1016/S0038-0717(02)00279-1
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