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There is a fascinating trend with using worm castings for lawn fertilization that I’ve been researching. The castings offer a lot of benefits compared to traditional fertilizers and, assuming you have a worm bin, you can produce an ongoing supply. But like everything else in life, it’s not without its issues.
Why use worm castings on your lawn? Worm castings contain multiple nutrients that are beneficial for lawns in an organic, moisture-retaining delivery system. They provide an impressive balance of nitrogen, phosphorous, potassium (NPK) and more.
Let’s look at some of the reasons why this trend is becoming so popular as well as some of the challenges that come with it. And since talk is cheap, I’ll be referencing literature and studies from universities to show that this is not just some crazy trend but a scientifically-sound lawn improvement strategy.
Why Use Worm Castings As A Lawn Fertilizer?
I realize that this concept may sound off the wall but there are real benefits to using worm castings on your lawn.
We’ve all heard of NPK, right? It’s the Nitrogen-Phosphorous-Potassium ratio that fertilizers are identified by. Well, worm castings contain these three nutrients in a very balanced ratio of 5-5-4 (source).
They also contain other valuable nutrients including calcium, sulfur, and iron. According to the University of California Agriculture and Natural Resources, worm castings are 100% organic humus that contains beneficial microorganisms that repel insects and inhibit soil-borne diseases of plant life.
Of course, the number of nutrients in your worm castings is dependant on what you are feeding them but that is perhaps the biggest advantage. You have absolute control over the nutrients that you feed compost worms and therefore control over the nutrients that your lawn is receiving. Compare that to the confusing ingredients found on the labels of many store-bought fertilizers!
In addition to nutrients, worm castings also hold microorganisms that are beneficial to both the soil and grass. In fact, one study found that castings hold up to 20 times more microbial activity than native soil (source). These microbes work to bring your soil to life, enhancing the quality, texture, and richness of the soil, providing a better growing environment for your lawn.
Another interesting benefit offered by worm castings is their incredible ability to retain moisture. In fact, they improve the soil’s water-retention capacity and reduce compaction (source). This can be of tremendous benefit for reducing water use helping grasses survive drought conditions.
Improved Soil Aeration And Drainage
I am not an advocate of topdressing alone. I feel that you significantly compound the benefits of your efforts by performing core aeration and deep core integration prior to topdressing. In this case, you can gain the added benefit of improving the aeration of your soil and it’s drainage by including worm castings in your topsoil mix after core aerating.
Some of the worm castings will find their way into the core holes as the topsoil mix is spread. This is especially beneficial to soils like clay that are prone to heavy compaction. Read more about my five-step process for improving clay soil.
A True DIY Organic Lawn Fertilizer
Perhaps the greatest benefit of using worm castings is that is really is an organic lawn fertilizer that you can make yourself. There are always safety concerns with chemical fertilizers, especially when it comes to kids and pets. But worm castings are organic fertilizer that you can be assured contains no dangerous chemicals, especially when you own the worms and have control over what they eat.
This short YouTube video shows the dramatic impact that worm castings can have on a lawn.
The Challenges Of Using Worm Castings As Lawn Fertilizer
So there is no doubt that worm castings offer benefits for your lawn and soil but there are a few challenges to taking advantage of this incredible organic fertilizer.
You Need To Be Vermicomposting
To take advantage of worm castings to fertilize grass, you need to be vermicomposting (composting with worms). You can build a DIY worm bin or buy one online (click here for our top recommended worm bins).
Potential Solution – If you don’t want to deal with vermicomposting, you do have the option of buying bagged worm castings. You may be able to purchase these locally or you can purchase organic worm castings online (link to Amazon). This, of course, negates the benefit of creating free fertilizer on your own but it is an option if you are seeking the benefits of worm castings but don’t want to manage a worm farm.
Worms can only poop so much. Unless you have a ridiculously large worm farm, you will likely not have enough castings to spread across your lawn on their own. But don’t fret, there are several ways to get around this.
Potential Solution – The simple fix for having a limited supply is to mix it with something else before spreading. You can mix and spread with traditional fertilizer, for example. Instead of making worm castings a replacement for store-bought fertilizers, think of it as an amendment to add additional nutrients and moisture to your lawn. You can also mix it with sand or regular compost to ensure even spreading across the yard (see How To Spread Worm Castings below). And perhaps the best solution when your supply is limited is to create a worm tea spray (more on that later).
Topdressing A Lawn With Worm Castings
Topdressing your lawn with worm castings is a simple process that can add valuable nutrients and microorganisms to the turf and soil. The worm castings offer a slow-release of moisture and minerals that will not burn the lawn.
This video outlines the process in under 3 minutes:
When applying worm castings as a topdressing, this is the general process and a few things you will need to keep in mind:
How To Spread Worm Castings
- A Broadcast Fertilizer Spreader – As demonstrated in the video, many broadcast spreaders can be used to spread castings. Spreaders usually offer settings that allow larger amounts of fertilizer to be spread at once. This setting actually opens the bin with a wider opening that can allow larger particles like worm castings to be spread. If you have a fertilizer spreader, check and see if this setting might work for you.
- Compost Spreader – Another solution for worm castings is a compost spreader like this one (link to Amazon). These actually have screening that is designed to allow larger particles like worm castings to fall through the screen into the lawn as it is tumbled. These are pricer but if you are planning on spreading regular compost with worm castings mixed in, this is probably the best solution.
- Worm Tea Spray – Here’s a third option that many people wouldn’t think. Using this approach, you soak, the worm castings in water to create what is known as worm tea. You can then use a garden hose sprayer to spread the nutrients across your lawn. Worm tea will not burn a lawn (source). Also, the variety of microbes that are introduced into the soil helps to prevent any single bad organism from obtaining dominance (source).
When To Use
Worm castings can be spread across the lawn with the same frequency and intervals as any chemical-based fertilizer. Mixing the castings with compost, topsoil, or another aggregate will help to ensure even distribution and benefit to the entire lawn if you do not have enough to spread alone. Just make sure that when spreading with compost or topsoil that you do not completely cover the grass. It should be worked into the lawn so that the grass still receives sunlight.
Using worm castings for lawn fertilization is an excellent use of vermicomposting efforts and can help your grass to thrive. If you are interested in vermicomposting to create your own organic lawn fertilizer, be sure to check out our top recommended worm bins.