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How to Use Worm Castings: An Expert’s Guide with Tips and What You Need to Know (2024)

Let's start with the #1 reason we love 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.

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

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If you are already a worm castings convert, click here to skip down to the sections on How to Use Worm Castings in your Garden, House Plants, Lawn, and More!

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

Castings are so effective in plant growth they are a popular product among organic growers and are coveted by vineyard and cannabis growers, home gardeners, and many other grow industries.

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

Benefits of Earthworm Castings

how do worm castings work, why worm castings work, how to use worm castingsThe reason worm castings work so well is that worms and plant root systems have developed a symbiotic relationship where worms and castings provide the  biology (think nematodes and protozoa), minerals, and nutrients that plants need to grow and thrive
 

Worm 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 helps create 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
    how to use worm castings, will worm castings help all plants, are worm castings good for gardens
    Worm castings will help anything with roots grow!
     

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

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

    How to Use Worm Castings

    Worm castings can be used with existing potted plants, gardens, and lawns, or with new plantings and seedlings.

    The application and use will differ, though, with castings being mixed into the potting medium for new plantings and placed on the surface and gently kneaded into the soil for existing plants.

    Here’s a breakdown for using castings 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

    Here’s one last tip on 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 the 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. 

    Frequently Asked Questions: How to Use Worm Castings

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

    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 I use too many worm castings?

    No, castings will not burn or harm your plants at any application level. Although castings are chock full of nutrients, minerals, and active biology, plants will only absorb what they need to thrive. 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.

    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 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 with higher quality. 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.

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

    We recommend using a ratio of 15-20% castings to 80-85% soil or potting mix.

    Where can I buy castings?

    Castings are available through many worm farms, either in their online store or on Amazon. You can also buy worm castings at many retail locations, form big box locations like Home Depot to smaller lawn and garden shops. We sell them in small batch and bulk sizes at Brothers Worm Farm.

    where to buy worm castings, where to buy worm castings online, how to buy worm castings

    Good luck and happy growing!

    Comments

    Brothers Worm Farm

    Worm casting actually aren’t high in nutrients, they can be high in minerals depending upon what the worms have been feed & has been added. It’s been proven that the NPK rating of castings is very low. The casting absorb and slowly release the existing nutrients in the soil to allow plants to have access to them. If there’s no nitrogen in the soil the casting and microbes won’t provide enough for the plant to thrive, but adding a mix of good compost and castings will provide the plant with the nitrogen it needs. If I’m incorrect I’d love see the scientific research on this. I do agree that casting are sometimes fugal dominant and some are bacterial dominated. I also agree that there are high and low quality castings out there, but I’m not sure if the bedding really makes a difference in the microbial life since the transformation happens in the gut of the worm, so anything that passes through their body will have a high amount of microbes. Again, if I’m incorrect please let me know by posting a link to prove this. I’d really love to know how the bedding type changes the composition, other than the fugal vs bacterial castings. I find this subject super interesting and I’m not trying to put down or bash this article, I’d just like see links to back this information. All the scientific papers I’ve read on the subject disagrees with some of the things said here.

    Brothers Worm Farm

    Come out and Purchase worm castings at your farm

    Brothers Worm Farm

    Hi, I have existing plants that could use a little fertilizer. Do worm castings and Miracle Grow basically take the plant to the same “place” but the road used to get there is different. I am trying to understand if I use worm casting if I still need to use my fall chemical fertilizer?
    Also, what dates are associated with use in “Fall”? Is this just any time before Dec 21 (Winter solstice) or does “fall” mean the Sep/Oct time frame? I am in the Pacific Northwest – so it doesn’t get very cold here as compared to the rest of the country. It rains almost every day from Oct-June and it might snow for a week or two in winter but our ground pretty much never freezes…I’ve never seen it freeze. Mud – sure, more mud that I care to remember but never “frozen” ground.
    Finally, I want to use worm casting on Doug Fir Trees, Cedar Trees, Western Hemlock Trees, Boxwood shrubs, Sword Ferns, recently planted daffodil bulbs and bareroot Fiesta Daisy planted last week (Nov 3rd). Will all of these plants benefit from worm casting?
    Thanks for your help.

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