How Much Vermicompost to Add to Potting Soil

If you are mixing up your own potting soil, you will need to add a source of nutrients. And it doesn’t get much better than vermicompost: it improves the soil’s structure and moisture retention capacity and is a source of slow-release nutrients. But how much vermicompost should you add to potting soil?

Vermicompost is an excellent slow-release fertilizer and soil conditioner in potting soil. Recommended substitution rates range from ten to forty percent vermicompost. To make a universal potting mixture, thoroughly mix topsoil, coco-peat, and vermicompost in a 1:1:1 ratio.

If you don’t use enough vermicompost in your potting mix, you will be missing out on the benefits it can offer. But too much can cause damage because it provides too much nitrogen or is too high in pH for the plants you are growing. Read on to find out all you need to know about adding vermicompost to potting soil.

The Ideal Ratio of Vermicompost to Potting Soil

There is considerable debate over how much vermicompost to use in potting soil, with suggested substitution ratios ranging from 10 to 100%

However, using too much vermicompost can have detrimental effects, and it is best used as a soil additive in the right proportion. We’ll guide you as to what constitutes the right proportion.

A study published in Bioresource Technology investigated the effect of substituting different percentages of the soil with vermicompost on the growth and yield of bell peppers. This study found that beneficial effects increased up to 40% substitution and declined after that (as they added even more vermicompost).

Vermicompost is an excellent soil amendment, but you can have too much of a good thing. Additionally, you don’t always want to add the same amount of vermicompost to your potting soil mix. You can get into varying the ratio once you have experience working with this stuff.

For a universal potting mixture suitable for most types of plants and most containers, thoroughly mix in approximately 30% vermicompost into a potting soil mixture that you have purchased.

Alternatively, you can create your own potting soil mix by mixing one part topsoil to one part coco-peat (for its moisture-retentive properties) and one part vermicompost. In other words, shoot for a 1:1:1 ratio of topsoil to coco-peat to vermicompost.

You can also add perlite or vermiculite to the potting mix to aid in moisture retention. If you don’t have coco-peat, use two parts topsoil to one part vermicompost (a 2:1 ratio of topsoil to vermicompost).

Soil that is too sandy drains too freely; vermicompost will help correct this problem. On the other hand, soil containing too much clay will hold onto water too much and won’t drain enough. To fix this problem, you should add some sand to the soil proportion of the mix.

Whatever the specific amendments you need to make to your soil, aim to have around 30% of the total be vermicompost to create a universal potting mixture.

If you are using the mixture in terracotta pots (or other unglazed pottery), increase the ratio of vermicompost slightly and add more perlite or vermiculite. This is because these pots lose water more readily than plastic pots, so you will want to increase the amount of water-retaining constituents in the potting soil mix.

Using Vermicompost for a Seed-Starting Mix

Skip the soil if you are mixing a potting mix for starting seeds. Soil tends to clump and does not provide the optimal conditions for allowing seeds to germinate. In nature, seeds germinate under the slightest dusting of sand or in the shade of rocks, leaf litter, etc.

You can mimic leaf litter’s beneficial germination environment by mixing up one part coco-peat and one part vermicompost (a 1:1 ratio).

This mixture provides the ideal environment for germination. The mixture will retain enough water yet drain freely. In addition, the vermicompost supplies nutrients to supplement the store in the seeds, boosting the baby plant’s growth and giving them a strong start in life.

Using Vermicompost as a Topdressing in Pots

If you have existing pot plants, you can also give them the benefits of vermicompost. Supplement the soil in their pots with the addition of vermicompost.

Add a thin layer of vermicompost onto the soil’s surface in the pots about every two weeks, and water it in so that the nutrients and other beneficial ingredients of vermicompost reach the plants’ roots.

We recommend that you keep neat vermicompost away from the stems of delicate plants, as the nitrogen content may be too high and burn them. However, provided you exercise this precaution, this is an excellent way to feed your plants.

You can also use the liquid that drains out of your worm farm to water your pot plants, sometimes known as worm tea. Dilute it in the ratio of one part worm tea to twenty parts water (1:20), and use the diluted tea to water your pot plants.

The Benefits of Adding Vermicompost to Potting Soil

Vermicompost has multiple benefits for potting soil, improving soil quality in various ways:

High Levels of Essential Nutrients

Vermicompost contains high organic carbon, nitrogen, potassium, phosphorus, magnesium, iron, sulfur, and calcium. It also contains sodium, copper, zinc, manganese, boron, and molybdenum. It, therefore, provides all the essential nutrients for plant growth, flowering, and fruiting.

Growth Encouragement

Vermicompost a encourages encourages plant growth, the growth of new leaves, and the quality of produce if you are using it on crops such as tomatoes.

A Viable pH Buffer

Vermicompost is neutral in pH (pH 7), which means that it can act as a buffer for soil pH, preventing extremes of pH that would prevent plants from absorbing nutrients.

Free From Heavy Metals, Pathogens, & Weeds

Vermicompost is free of toxic heavy metals, as the worms eliminate these elements as they process the feedstock. It is also free of pathogens (disease-causing organisms) and weed seeds, provided you haven’t fed the worms weeds that have gone to seed).

A Source of Vitamins & Enzymes

Vermicompost contains vitamins, plant hormones such as auxins and gibberellins that stimulate plant growth, and enzymes that are offensive to common pests such as aphids, whiteflies, and spider mites, helping to repel them.

Beneficial Micro-Flora

Vermicompost abounds in beneficial micro-flora such as phosphorus solubilizers, nitrogen fixers, and cellulose-decomposing bacteria, which enhances the health of your soil.

Possible Earthworm Activity

Vermicompost also contains earthworm cocoons, which leads to an increase in the earthworm population in the soil in your pots, which is of ongoing benefit to your plants as they help decompose organic matter in the ground.

Improved Soil

Vermicompost improves the soil’s texture, structure, porosity, aeration, drainage, and moisture-holding capacity as well. Vermicompost can hold nearly nine times its weight in water. The ongoing action of the worms in your pots serves to maintain this capacity.

Easy Storage & No Smell

Last but certainly not least, vermicompost is easy to handle and store and smells rich and earthy, with no offensive odor.

The Effects of Too Much Vermicompost in Potting Soil

Despite the benefits of vermicompost, there are certain drawbacks to using too much.

The neutral pH of vermicompost means that using high amounts will raise the pH of the soil too high for acid-loving plants. In addition, the high nitrogen content of vermicompost, although it stimulates growth in plants, might be too much for delicate plants in excess and burn their stems. 

A mix with too much vermicompost will lose too much volume when watered. Keep the structure of your potting soil mixture right by using enough topsoil.


Hopefully, we have answered your questions about using vermicompost in potting soil as a soil conditioner. Use the recommended ratios for different applications, and you should soon see dramatic improvements in your plants’ growth rates, health, and yields!

Alexander Picot

Alexander Picot is the founder of and its lead content writer. He created the website in 2022 as a resource for horticulture lovers and beginners alike, compiling all the gardening tips he discovered over the years. Alex has a passion for caring for plants, turning backyards into feel-good places, and sharing his knowledge with the rest of the world.

Recent Posts