Why Add Worms to Your Garden: Benefits of Worm Castings

By: Angela Judd | July 10, 2024

Guest Post by Zach Brooks, Owner of Arizona Worm Farm

Most of us garden to have healthy fruits and vegetables to eat. When you add worms to your garden, the benefit of the worm castings those worms produce is that you will have better living soil. Better living soil will produce better fruits and vegetables with less water and other fertilizer. Healthier for you. Healthier for the planet.

”Worms literally move the earth in the process of their meanderings. Their passage through the earth aerates the soil, and the natural chemistry of their guts renders soil and plant matter into fertile pellets”¹
Charles Darwin

Article Outline

The Benefits of Adding Worms and Worm Castings to Your Garden
The Science Behind the Benefits of Worm Castings
The Science Behind the Nutrients Plants Need
How Microbial Life in Soil Helps Plants Use the Nutrients in the Soil
Encouraging Microbial Activity Enables Plants to Help Themselves
How to Imitate Nature in Your Garden With Worms and Worm Castings
How Many Worm Castings Should I Add to My Garden Beds?
Do I need to add worms?
About Zach and the Arizona Worm Farm

Why Add Worms to Your Garden: Benefits of Worm Castings — Red Wiggler Worms at Arizona Worm Farm

The Benefits of Adding Worms and Worm Castings to Your Garden

I own the Arizona Worm Farm and want you to buy worm castings for your garden. I want to take the time to explain what worm castings do for your soil, but let’s start with the benefits of worms and worm castings.

The USDA says, “Worm castings are high in plant-available nutrients and help improve soil structure and water holding capacity.”² PennState³ quotes their studies that tell us worm castings will add beneficial microbes to your soil that will do all of the following:

They “make” food: Microbes break down organic matter into digestible food for your plants.
They protect your plants: Microbes can outcompete “bad” microbes, produce toxic compounds, or parasitize them. They can also activate plant immune responses to help them fight disease.
They encourage plants to grow and heal: Microbes release phytohormones that can regulate plant growth and trigger immunity.
Microbes help your soil use and retain water better. They also help absorb and recycle water in the soil. They extend the reach of your plants’ roots to help the plants access more water.
They foster healthy growth: Microbes can help plants tolerate stress

The Science Behind the Benefits of Worm Castings

The science is a long journey into the details, but it begins with a simple idea. Nature grew abundant fruits and vegetables long before we showed up with our NPK tests, Miracle Grow, pH balancers, and mycorrhizal amendments. So, if we can imitate Nature in our yards and gardens and get out of the way, our gardens will thrive.

Soil is made up of five basic building blocks – minerals, organic matter, living organisms, water, and air.

Minerals are tiny pieces of rock that have broken down over time.
Organic matter (what soil scientists call Detritus) is partially broken-down leaves, grass, mulches, and plants. For most of us, this is the stuff that falls from our trees and plants, plus the compost we add every time we plant.
Healthy soil is made up of almost 50% water and air.

The Science Behind the Nutrients Plants Need

Plants need Nutrients to Grow. There are three primary macronutrients that all plants need to grow healthy and strong – nitrogen (N), phosphorus (P), and potassium (K). That’s the NPK you see on fertilizer labels. They are the nutrients that plants need most to grow.

Nitrogen helps plants grow leaves and stems.
Phosphorus makes flowers bloom, and roots grow.
Potassium supports the plants’ immunity to disease and affects the fruit’s quality.

There are also many macronutrients—calcium, magnesium, and sulfur—and micronutrients —chlorine, boron, copper, iron, manganese, zinc, molybdenum, and nickel – that plants need to grow.

It is also important to note that the balance of these nutrients is critically important. Too much or too little of a micronutrient can keep a plant from absorbing macronutrients. For example, Boron deficiency commonly results in fewer flowers per plant. You might look at your plant and add Phosphorus (because, duh, Phosphorus makes flowers bloom), when your soil has plenty of Phosphorus and not enough Boron. More on that later.

Healthy artichoke plants at Arizona Worm Farm

The pH (short for the power of Hydrogen), which measures the acidic/basic level of soil and water, can impact how plants consume these nutrients. Most crops grow best in soils with a pH of 6.5-6.8. Here in the Phoenix area, our water tends to be close to 8, so our plants may have difficulty accessing certain nutrients. Again, more on that later.

If everything is right and in balance, your plants will grow and be productive, the fruit and vegetables they produce will be of higher quality, and your plants can better resist disease and pest pressure.

How Microbial Life in Soil Helps Plants Use the Nutrients in the Soil

Let’s get nerdy. Microbes are also present in soil. They are quite small (a teaspoon of worm castings can contain one billion bacteria representing 10,000 species and three to four yards of fungal hyphae), but they play a critical role in feeding our plants.

The organic matter in our soil holds most of the nutrients plants need in complex molecules like proteins, fats, and carbohydrates that plants can’t use directly. To make these nutrients available for plants, soil organisms like bacteria, fungi, earthworms, and pill bugs decompose the organic matter. This process converts nutrients into forms that plants can absorb and increases the soil’s ability to retain nutrients like calcium, potassium, and magnesium.

Healthy Soil with worms — Red Wiggler Worms

Microbes take the food in the organic material and convert it into forms our plants can eat. We call that “Nutrient Cycling“.

“A nutrient cycle is the cyclic pathway by which nutrients pass through to be recycled and reutilized. The pathway comprises cells, organisms, community, and ecosystem.”⁴

In this process, nutrients get absorbed, transferred, released, and reabsorbed. It is a natural recycling system of mineral nutrients. Nutrients consumed by plants and animals are returned to the environment after they fall off trees or die (or, in the case of animals, when they poop) and decomposition, and the cycle continues.

“Soil microbes decompose organic matter to release nutrients. They also trap and transform nutrients into the soil, which plant roots can take up.”⁵

Encouraging Microbial Activity Enables Plants to Help Themselves

So, soil microbes convert what is in the organic matter into food the plants can eat. But Nature takes it to an even better place. Plants and microbes have “conversations” – plants produce exudates (sugars) that feed the microbes that make the nutrients plants need. For example, while many microbes fix atmospheric nitrogen, some provide specific nutrient availability to your plants. Rhizobia-legumes provide N2-fixation. Plant-arbuscular mycorrhizal fungi assist with phosphorus availability, and arbuscular mycorrhizal fungi forage soil phosphorus through their hyphae root system.

Plants can foster the growth of the microbes that produce the specific nutrients they need. When we talked about a need for balance in macronutrients and micronutrients (a couple of paragraphs above) – we now see the brilliance of Nature (and the importance of microbially active soils). Your plants will tell your microbes when they are out of balance, and the microbes will help retrieve and supply the nutrients your plants lack.

With many micronutrients, too much is as bad as too little. Getting your soil balanced by adding micronutrients is the process soil scientists with advanced degrees get right at giant agricultural companies with labs, tests, and expensive machines. I have always found it impossible to get right in my backyard. Conversely, using worm castings to add microbes that talk to plants to balance naturally is demonstrably easier – and has never failed me.

But wait, there’s more!

The National Institute of Health reports many studies that show microbes can increase or decrease the pH and thus produce a more or less suitable environment for themselves. Microbes like 6.8 to 7.0 can modify their environments to be closer to 7. They will drive the pH to be what your plants prefer.

How to Imitate Nature in Your Garden With Worms and Worm Castings

We don’t need to understand soil science to get this right. We just need to make sure our gardens and yards have the basics:

Organic matter (decomposed material (plants, insects, food scraps) or compost you make yourself or get from The Arizona Worm Farm).
Microbes (from worms or worm castings)
Water and Air

If you continuously build up the organic matter in your garden by adding compost to your garden beds regularly, using mulch, growing cover crops, and adding manure, you will have the building blocks in place. By adding worms or worm castings, you add the life you need to transform that material into exactly the nutrients your plants need to thrive.

The bottom line is that microbially active soil with lots of organic matter will fine-tune itself to produce abundant growth. The National Center for Biotechnology put it this way:

“Vermicompost enhances soil biodiversity by promoting the beneficial microbes which in turn enhances plant growth directly by production of plant growth-regulating hormones and enzymes and indirectly by controlling plant pathogens, nematodes, and other pests, thereby enhancing plant health and minimizing the yield loss.”

The benefits of worm castings can be summarized in this way: worms grow helpful microbes in their guts that end up in their castings. When moved promptly, those microbes flourish in gardens with rich organic materials.

How many worm castings should I add to my garden beds?

For established beds, apply 4 cups per 4×8 bed.
In new beds, aim for around 5% worm castings (11 gallons per 4×8 bed).
Layer them on top of the soil and lightly water them in.

Learn more about how to amend your garden soil in this guide.

Amending Soil with worm castings to prepare beds for planting

Do I need to add worms?

I am often asked if I need to add worms to my garden. In many geographies, creating a welcoming environment (lots of organic matter and regular water) will attract worms. They will “show up”. If you live in an area with moist, loamy soil (like, for example, Minnesota or New Jersey – even Central Phoenix in the irrigated sections), you will almost certainly attract worms – and there is no reason to buy them to add. If, on the other hand, you live in a desert where the native soil is dry, lacking in organic matter, sandy, or just very hard – you will have a hard time attracting enough worms to have a positive impact on your garden.

And, as I move from Soil Nerd to Worm Nerd, I will tell you that there are hundreds of species of worms. The worms fit into three general categories:

Deep burrowing worms (Anecic)
Shallow-burrowing earthworms (Endogeic)
Surface-dwelling (Epigeic)

The worms you will attract to your gardens tend to be Anecic or Endogeic and move quite deep in your soils. They don’t stay where you put them, and you can’t control their movements. Because they only breed in very deep burrows, they can’t be bred in normal worm farms like ours. The worms we raise and sell at the Arizona Worm Farm are Epigeic – they operate in the top three or four inches of soil and don’t burrow (which means they also don’t wander to your neighbors or fields).

Red Wigglers are perfect worms for worm bins and in-garden worm composting. We recommend adding these worms to your garden. If you feed them regularly and keep them properly watered, you will never have to buy them again.

Sources used for this article about why to add worms and the benefits of worm castings:

Additional information about adding worms and the benefits of worm castings:

About Zach and the Arizona Worm Farm

Zach Brooks owns and founded The Arizona Worm Farm in Phoenix, Arizona. This 10-acre, fully sustainable, off-the-grid farm uses waste by-products to grow food and produce castings, worm castings, tea, and compost. Zach has an MBA and completed extensive Sustainability coursework from ASU’s School of Sustainability.

The Arizona Worm Farm is your place in Phoenix to get worms, worm castings, compost, soils and tea. They are working to produce the most powerful, live, active natural fertilizer on the planet!