How to Use Worm Castings: An Expert’s Guide to Earthworm Castings for Plant Growth (2025)

Let's start with the #1 reason we love to use worm castings - worms and their castings are the culmination of 500 million years of evolution and are much safer, less toxic, and more effective than harsh chemical fertilizers.

Worm castings are frequently referred to as “black gold” and "the superfood of plants", and they contain minerals, nutrients and active biology that are proven to improve soil structure and aid in plant and root growth. 

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Looking to purchase lab-tested, biologically-rich worm castings for your plants or garden? See our bulk and smaller sizes here!

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Earthworm castings are so effective as a natural fertilizer in plant growth that they are a popular product among organic growers and are coveted by vineyard and other professional growers, home gardeners, and many other grow industries.

And unlike chemical fertilizers, castings are an all-natural, long-lasting, and versatile soil amendment that helps plants increase yield, grow larger root mass, and resist diseases, without the damaging side effects of chemical fertilizers!

What are Worm Castings & Vermicompost?

Worm castings are the natural byproduct (or "poop") of composting worms like red wigglers. As worms digest organic matter, they produce castings that are rich in water-soluble nutrients, beneficial microbes, and organic compounds that plants love.

Worm castings act as a natural fertilizer and organic soil amendment that improves soil structure, increases microbial activity, and delivers a slow-release fertilizer that won’t burn plants—making them one of the most effective natural soil amendments available.

Vermicompost is very similar to worm castings - vermicompost contains a high concentration of worm castings along with other organic material like compost that was not fully processed by the worms.

Vermicompost provides many of the same benefits as a soil amendment as worm castings, usually at a lower price since the process to create vermicompost requires less labor and processing.

Benefits of Earthworm Castings for Plants

Earthworm castings are alive with microbes and bacteria and are full of organic matter, and this biology has been proven through numerous scientific and academic studies to help plants grow larger root mass which leads to greater yield and the prevention of disease from insects and the environment.

So how do castings have this effect on plants? They do it with:

• A rich population of beneficial fungal and bacterial feeders - This active biology amends soil to create an optimal, fertile soil structure by releasing nutrients that are easy for plants to uptake.
• Improved soil porosity - The size and composition of castings promote air flow and improve water retention, both of which aid in root growth.
• A wide variety of water soluble minerals and nutrients - These nutrients are easy for plants to absorb and better than traditional fertilizers, which are toxic and often lost before plants can absorb them.

Where to Use Worm Castings

Castings are an excellent soil amendment for virtually any plant type or grow system, including:

• Vegetables, fruits, and herbs 
• Gardens and raised gardens 
• Lawns, trees, shrubs, and vines 
• Perennials and Annuals 
• Potted plants and hanging baskets

Worm castings can also be used with any type of planting - from new seedling plantings or established plants and flowers to vegetables gardens, lawns, trees, and shrubs.

Basically, if it has a root system, lives in the soil, and grows, it will love earthworm castings!

How to Use Worm Castings

Worm castings can be used in gardens, lawns, potted plants, and seedling starts by mixing into soil or applying as a top dressing. For new plantings, blend 15–20% earthworm castings into your potting mix or garden soil. For established plants, simply sprinkle 1/2 to 1 inch of castings around the base, gently work them into the soil, and water lightly.

What is the Best Way to Apply Worm Castings

The best way to apply worm castings depends on the planting stage your fruits and vegetables are in.

For existing plants, fruits, vegetables, trees or lawns, castings will be applied directly to the soil around the root base of the plant. 

For new plantings or seeds, castings should be applied in each seedling hole near the seed and area where the roots will grow.

Here’s a breakdown for using castings or vermicompost for virtually any home horticulture or garden project:

Type	Application & Amount to Use	Frequency
Existing Vegetables, Perennials, & Annual Flowers	Spread 1-2 inches of castings on the soil above the plants’ root systems. Gently work the castings into the soil and water lightly.	2-3 times per year in early spring, early summer, & early fall
Existing Potted Plants, House Plants, & Hanging baskets	Sprinkle ½ to 1 inch of castings on the top of the soil. Gently knead the castings into the soil and water lightly.	Every 2-3 months
Existing Trees, Shrubs, Vines, & Roses	Apply a 2-3 inch layer of castings around the base of the plant and root system. Gently knead or rake into soil and water lightly.	2-3 times per year in early spring, summer, and fall
Existing Gardens & Flower Beds	Apply a 1-2 inch layer of castings (~5 pounds per 10 square feet) to the garden or flower area. Knead or rake into the soil where possible and water gently.	2-3 times per year in early spring, summer, and fall
New Vegetables, Perennials, & Annual Flowers	Line each seedling hole with ½ to 1 inch of castings, or each plant hole with 1 to 2 inches of castings, insert seed or plant, and cover with soil or your grow mix. If you are planting a new garden or raised bed, you can instead mix 15% to 20% (1:5 ratio) castings with your soil or favorite planting medium before seeding or planting.	Once at planting, then top dress with ½ inch of castings every 2-3 months from spring to fall.
New Potted Plants, House Plants, and Hanging Baskets	Use 15% to 20% (1:5 ratio) castings with your soil or favorite planting medium.	At planting, then top dress with ½ inch of castings every 2-3 months
New Trees, Shrubs, Vines, & Roses	Mix 15% to 20% (1:5 ratio) castings with your soil or favorite planting medium before planting. Line plant hole with mixture, insert plant roots into the mixture and cover with additional 1:5 castings to soil mixture.	At Planting
New Gardens & Flower Beds	Mix 15% to 20% (1:5 ratio) castings with your soil or favorite planting medium before planting.	At planting, then top dress with 1-2 inches of castings every 2-3 months
New & Established Lawns	Apply 20-25 pounds of castings for 100 square feet of lawn space. Water lightly.	2-3 times per year (spring and fall)

How to Store Worm Castings

The nutrients and biology in castings are so dense that a little bit goes a long way. If you have castings left over, just store worm castings covered and away from direct sunlight or moisture.

Covering the worm castings will keep them from drying out and protect them from UV radiation which can harm the beneficial biology in castings. Worm castings will usually last 12-18 months if stored properly. 

How to Make Worm Castings for Plants

Worm castings are made by feeding composting worms (like red wigglers) a steady diet of organic matter (e.g., manure, fruit/vegetable waste, compost) in a controlled bin.

Over time, the worms consume and break down the material and leave behind worm castings. The castings can then be harvested using a screen and applied to plants, gardens, and lawns as a natural, biologically-rich soil amendment.

Frequently Asked Questions: How to Use Worm Castings

We’ll end this post on how to use earthworm castings by covering a few frequently asked questions and tips we’ve learned about earthworm castings.

How often should you apply worm castings?

Worm castings are best applied 2–3 times per year, typically in early spring, summer, and fall. For potted plants, a light top-dress of 1/2 to 1 inch around the base and root system every 2–3 months is ideal.

Can you put worm castings on top of soil?

Yes, worms castings can be put directly on top of soil. However, this would usually be done only for existing plants or on lawns. For existing plants, place castings on the soil around the base of a plant and covering an area where the root ball should be under the soil. Then knead the castings into the soil and water lightly.

Should worm castings be wet or dry?

Worm castings should be slightly moist—like damp coffee grounds—not wet or bone dry. This moisture helps preserve the beneficial microbes and ensures easy application and soil integration.

How to use worm castings in vegetable garden?

To use earthworm castings for a vegetable garden, apply the castings by top-dressing existing vegetables with 1/2 to 1  inches of castings and gently mix the castings into the soil. For new plantings, line seed holes or rows with castings or mix them directly into the garden soil and then lightly water the area.

Are worm castings good for all types of plants?

Yes, worm castings can help any plant, tree, shrub, or grass grow. The biology, minerals and nutrients, and composition in castings will improve soil structure and provide the building blocks plants and their root systems need to thrive.

Can you use too many worm castings on plants?

No, castings will not burn or harm your plants even in large amounts.

Studies have shown, however, that worm castings do not help plant growth above a certain amount, so the generally accepted amount of worm castings to use is 15-20 % castings to 80-85% potting or growing medium.

Although castings are chock full of nutrients, minerals, and active biology, plants will only absorb what they need to thrive so there isn't any risk of using too much worm castings. 

Are there different types of worm castings?

Yes! Worm castings will either be fungal (meaning they have lots of fungi) or bacterial (meaning they have lots of bacteria) in nature. Although most plant life will benefit from fungal or bacterial castings,  annuals and vegetables like bacterial soils while perennials, trees, lawns, vines, and shrubs prefer fungal soils and castings.

Are worm castings poop?

Yes - worm castings are worm poop and are the primary waste by-product of worms. Unlike regular waste, though, castings are biologically-rich and packed with microbes, minerals, and organic compounds that are beneficial for plant growth while improving soil health.

Are all worm castings the same?

No - all worm castings are not the same. Castings are impacted by several factors during their life cycle.

Bedding and feedstocks (like quality compost and manure) that are high in beneficial microbes will generally result in higher quality castings. Quality in = quality out! In addition, how the castings are processed and stored will impact their biological levels over time.

Finally, pH and the density of nutrients and minerals varies across castings based on the bedding and feedstock used by the worm farm.

What is the difference between worm castings and vermicompost?

Worm castings and vermicompost are similar materials that differ in their composition and concentration of worm castings.

Worm castings are mostly pure versions of worm excrement with very small pieces of other organic material that was not removed during the process that separates castings from other material in worm beds.

Vermicompost, by contrast, contains a high concentration of worm castings but also has a higher volume of other material like compost. 

Both products offer similar benefits to soils and plant growth - namely high levels of microbiology that act as a natural fertilizer by helping to release nutrients and minerals that are easily consumed by plant root systems.

How often should you use castings?

Earthworm castings are usually applied ~ 2-3 times per year based on the growing season of the fruit, vegetable, or plant. Early spring and late summer are generally the best times to apply castings to your garden, plants, or lawn.

How to use worm castings in the garden?

Apply 1/2 to 1 inches of castings across your garden beds around the base and root systems of your plants and vegetables, and gently work the worm castings into the top layer of soil. For new gardens, mix 15–20% castings into your soil blend before planting.

How many worm castings should I use per gallon of soil?

When mixing worm castings in a gallon of soil, use 20-25 ounces of worm castings per 100 ounces of soil. This corresponds to a ratio of 15-20 % castings to 80-85% soil mix. 

Academic studies have shown that worm castings do not help plant growth above a certain ratio, so the generally accepted amount of worm castings to use is 15-20 % castings to 80-85% potting or soil medium.

How to use worm castings for tomatoes?

For existing tomato plants, top-dress with 1–2 inches of worm castings around the base and water gently. For new tomato seedlings, mix castings into the planting hole or blend 15–20% into your soil mix. 

Are worm castings fertilizer?

Technically, no, worm castings are not fertilizer, but castings benefit plant growth in similar and better ways. Castings contain natural microbiology (fungi and bacteria) that release minerals and nutrients into areas around a plant's root system. These natural minerals and nutrients are easily absorbed and used by plants without the harmful effects of chemical fertilizers.

What should I do with my worm castings?

Worm castings can be used on nearly all plants—mix into the soil for new plantings, top-dress around  the base and root system for existing plants, or blend into potting mixes. Any leftover castings should be stored in a cool, dry, covered area away from sunlight and rain to preserve the living biology.

Where to buy worm castings for plants?

Worm castings are available through many worm farms and their online store. You can also buy castings at many retail locations, from big box locations like Home Depot to smaller lawn and garden shops.

We sell lab-tested, biologically-rich castings in small batch and bulk sizes at Brothers Worm Farm.

Good luck and happy growing!