All You Need to Know About Earthworm Castings

When you put biodiversity high on your list of garden goals, nature's creatures respond. Pollinating butterflies and bees are easy to see, but others — like earthworms — do their work underground. Earthworms benefit your yard and gardens in lots of different ways. As they move through soil, they create spaces that help air, water and nutrients reach plant roots. But earthworms also leave something behind: their castings.

In nature, castings are the little mudlike piles deposited next to holes where earthworms burrow into the earth. Put politely, they're an end product of worm digestion — one that can improve soil environments for indoor and outdoor plants. Castings are so beneficial, in fact, some gardeners raise their own worms. If that's your thing, we applaud you.

But if kitchen worm farms leave you a little queasy, relax. There's an easier way to bring earthworm castings to your garden and home.


Earthworm castings provide essential nutrients and help improve garden soil.

How Earthworm Castings Improve Soil

Earthworm castings are naturally full of organic matter and beneficial microorganisms that make your yard and garden a richer place. Biologically active, nutrient-rich earthworm castings provide essential plant nutrients, including iron,1 but they also work to improve your soil's structure — from potting soil mixes for indoor plants to outdoor garden soil.

Humus in earthworm castings helps increase soil's capacity for water retention, improve soil aeration and anchor plant nutrients that would leach away and be lost. Castings also feed beneficial soil microorganisms that produce, store and slowly release plant nutrients into soil to feed your plants.1

Pennington Rejuvenate Natural & Organic Garden Soil Mix is an easy way to bring earthworm castings to your native garden soil — without any mess or goo. Pennington Rejuvenate All Purpose Premium Potting Soil Mixdoes the same for your indoor houseplants or container gardens. These premium soil mixes also include added bio-stimulants to improve your plants' ability to take nutrients from your soil, indoors or out.

And don't worry — the earthworm casting granules in Pennington Rejuvenate garden and potting soil mixes won't constantly remind you where they came from. Their rich, earthy texture is a lot like fine garden compost or dry coffee grounds.


Earthworm castings help create living soil ecosystems for indoor plants, too.

How Earthworm Castings Benefit Plants

Besides all the ways they help your soil, earthworm castings also directly benefit plants. Research conducted over several years at The Ohio State University Soil Ecology Laboratory found that worm castings enhance seed germination, plant growth, flowering and fruit production. Those are pluses, whether you're growing flowers or vegetable gardens. Castings also curb certain plant diseases, such as crown and root rots and wilt disease, and they inhibit some pests, including mites, aphids and mealy bugs.2

Researchers at the Cornell University Department of Plant Pathology and Plant Microbe Biology also dug into castings to see what good they could do. Their research demonstrated that worm castings suppress damping-off disease — that's the soil-borne fungal disease that targets your seeds and new seedlings just when your hopes start to soar. They also found that castings naturally degrade the protective covering of some plant-damaging insect pests, regulate plant nutrient release and stimulate the natural cycle of nutrients from soil to plants.3

The impact of earthworm castings increases when they're worked into soil before planting or potting. With Pennington Rejuvenate Natural & Organic Garden Soil Mix and Pennington Rejuvenate All Purpose Premium Potting Soil Mix, you're already one step ahead. Earthworm castings work in harmony with other beneficial, sustainably sourced ingredients in these premium mixes. You and your plants enjoy the benefits — without raising worms, harvesting worm castings or mixing your own soil.


When you nurture your soil, it returns the love.

How to Bring Castings to Indoor And Outdoor Gardens

Bringing earthworm castings to indoor plants, containers or in-ground gardens is as simple as using Pennington Rejuvenate All Purpose Premium Potting Soil Mix for containers and Pennington Rejuvenate Natural & Organic Garden Soil Mix for your in-ground gardens outdoors. Here's how:

For Houseplants and Container Plants:

  • Check your container size against the guide on the product label. Make sure you have enough on hand for the job. This applies to hanging baskets, window boxes, large planters and raised beds, too.
  • Gently remove your plant from its old pot. Gently brush the old soil away with your hand. If your plant's rootbound, gently loosen or untangle the roots. Gently is the key word here.
  • Add a layer of Pennington Rejuvenate All Purpose Premium Potting Soil Mix to the bottom of your new container. Place your plant so the base of its stem will sit slightly above the surrounding soil when you're through.
  • Fill in around your plant with the potting soil mix until you cover the roots completely and the stem's base is at the same level it was at in its old pot. Firm the soil gently with your hands.
  • Water your newly potted plant thoroughly, allowing excess water to drain out the bottom. Then add more Pennington Rejuvenate All Purpose Premium Potting Soil Mix, as needed, to get the correct soil height in your pot.

For In-Ground Use, Including Flower Beds and Vegetable Gardens:

  • Measure the length and width of the garden area where you want to improve your native soil and nourish your plants.
  • Multiply the length by the width to get the total square feet. For example, a garden 6 feet wide and 4 feet long equals 24 square feet. Check the label to know how much soil your garden will need.
  • Cover the whole area with a 3-inch layer of Pennington Rejuvenate Natural & Organic Garden Soil Mix. For each 24 square feet of garden, you'll need five bags or 5 cubic feet of garden soil mix.
  • Then incorporate the layer of garden soil mix into the top six inches of your native garden soil to enhance the benefits of its sustainably sourced ingredients even more.
  • With Pennington Rejuvenate soil mixes, you can enjoy the goodness of nutrient-rich, biologically active earthworm castings and create a living sustainable soil ecosystem for your plants — whether indoors, in containers or in gardens outside.

At Pennington, we've been helping yard and garden lovers dream bigger and grow better since 1945. From where we stand, that means working with Mother Nature, not against her, and nurturing the earth placed in our care along the way. We're here to help you do the same.

Always read product labels thoroughly and follow instructions.


1. A. Timmerman et. al, "Composting Series: Worm Castings," Louisiana State University AgCenter.

2. The Ohio State University Soil Ecology Laboratory, Publications on Earthworms and Vermiculture, 2003-2008.

3. Cornell University Department of Plant Pathology and Plant Microbe Biology.