top of page

All About Worm Castings

Updated: Sep 5, 2021

Worm castings, the wondrous mixture of castings, enzymes, microbes and organic matter harvested from worm beds, has almost too many benefits to list! But always up to a challenge, we will attempt to extol its innumerable virtues and outline best practices to get the most from your worm poop.

Why it works

When you add worm castings to your soil, you help the soil absorb and retain moisture. The organic matter in worm castings helps the soil particles clump together, improving soil structure.

Worm castings contain myriad nutrients that are plant-available and released gradually into the soil.

Worm castings have a relatively low carbon-to-nitrogen ratio, making nutrients more available to plants and helping them to grow stronger and faster. The C:N ratio of worm castings typically falls in the range of 10:1 - 20:1.

Worm castings have a neutral pH, so they will not burn plants and they help create a perfect environment for all the right microbes and fungi to thrive.

Worm castings contain beneficial acids (humic and fulvic) which work by dissolving otherwise insoluble minerals, stimulating plant growth.

One of the most beneficial values of worm castings are their microbial properties. Worm castings boast a large and diverse population of microorganisms including beneficial mesophilic microbes that help with suppressing diseases.

Phenolic compounds in worm castings help to repel garden pests - either by their bitter taste or downright toxicity - through uptake in the root system (warding off caterpillars, aphids and spider mites). Studies have also shown that worm castings promote the growth of certain fungi that suppress parasites!

How much?

Bear in mind, a little amount of worm castings go a long way! In fact, there are studies focused primarily on optimal amendment ratios. Adding worm castings to soil works best when 10% - 40% by volume is added, with optimal values varying depending on the plant and its growth/flowering stage along with the electrical conductivity and soluble salts in your existing substrate. Over 40% volume can have negative impacts, including depressed growth, so no need to overdo it.

When creating a potting mix, we use about 20% worm castings and 20% compost mixed with our regular Hanover County (loamy/sandy) soil and a fine mulched pine for an airy and well draining soil. This works well for potted plants and container gardens. For new garden beds, we typically throw a handful of worm castings into the planting hole. For existing garden beds we top dress individual plants with about 1/4 cup per plant.

When to use

The benefits of worm castings can be seen from seed germination through flowering and fruiting. It's never too soon to start adding worm castings to your soil. Add it to your seed starter mix to help seeds germinate faster and to create a strong, healthy root system in your seedlings. Mix worm castings into the planting hole when transplanting from pot to ground. For existing gardens, top dress plants every 2-3 months.

Usage with cannabis

Cannabis loves worm castings! In fact, speak with any grower and they will typically prescribe the usage of worm castings in almost all stages of cannabis growth. Worm castings are valuable during the seedling stage, when their mild, balanced NPK is just the right formula for your little sprout. Apply a top dressing of castings when their first or second set of leaves (after the cotyledons) appear. Worm tea spray can be just the fix to protect your outdoor cannabis plants' foliage from pests and disease. Add worm castings at the plant's drip line every few weeks for a boost of beneficial microbes.

How to store

We store our worm castings right in the bin and bag it to order. At packaging, it will be moist and loose with fine particle clumps. If you do not plan to immediately use all of your worm castings, store the package in a cool, dry place away from sunlight. Leave the bag slightly open or poke holes at the top to allow passage of air, but not enough that it loses its moisture through evaporation. If moisture content drops precipitously (to <35%), the product will become dusty and difficult to apply - this also means the microorganisms have expired. When properly stored, worm castings will retain their benefits for 18 - 24 months.

Herb plugs using our house-made potting mix

The wonder amendment!

There's virtually no downside to using worm castings! So consider adding castings to your soil if you want any of the following benefits:

- Help soil absorb & retain moisture

- Improve soil structure

- Aid in the growth and proliferation of microbes

- Encourage root growth

- Allow plants to more effectively utilize and retain nutrients

- Help suppress disease and fight off pests

Our worm castings are typically available year-round and come in 3 & 10 qt resealable bags for pick-up or delivery in Richmond, VA. We also ship worm castings throughout the state of Virginia via ground. Live outside of Virginia? Contact us to check availability. We third-party test our worm castings to ensure nutrient measurements and microbial quality. Contact us if you have any questions about obtaining, using or storing worm castings.

Until next time, happy gardening!

Recent Posts

See All


bottom of page