Worm Castings vs. Seed Starting Mix

This blog post is a subsection of our Worm Castings 101 - Everything You Need To Know guide. In the 101 guide we cover multiple topics about worm castings, so if you'd like a more thorough walk through of what worm castings are and what they have to offer then click through to read more!


My knowledge of worm castings began many years ago as I sought a way to compost my kitchen scraps - and that quickly became a fascination as I came across some incredible experiments highlighting how significant of an impact worm castings can have on starting seeds and seedling growth.

Fruit and vegetable tests have resulted in yield improvements from 57% to over 200% as well as improvement in taste and appearance. - University of California Agriculture and Natural Resources 

Image of a seed starting experiment using worm castings
This experiment by AlboPepper 6 years ago is what first peaked my interest in utilizing worm castings for starting seeds. 

Are worm castings good for seed starting?

There are three primary reasons for why you want to use worm castings when starting seeds:

  1. Water Retention: For seeds to germinate, they need to be in a warm and moist environment. Because Worm Castings are 100% organic matter, they retain significantly more moisture than traditional seed starting mixes and this creates a more suitable environment for the seeds to germinate and begin to grow into seedlings.  
  2. Microbes: Just like humans, our plants health will be threatened by disease and pests. To prepare their "immune system" for this, we want them to be interacting with bacteria, enzymes, and biology from the beginning. One of the best part of worm castings are the bacteria and enzymes they are coated in while passing through a worm's digestive tract. These bacteria and enzymes help plants develop a strong immune system and ultimately grow more green, lush, and full of life. 
  3. Nutrients: As our seed germinate and begin to grow, they will quickly need nutrients in order to grow to their fullest potential. Because worm castings come from organic matter, there are nutrients available for the plant to put to use as it begins to put on its foliage growth

seedlings growing much larger in Mind & Soil's worm casting seedling mix than a store bought mix

A recent trial completed by West Coast Seeds showing plants growing significantly larger and more lush when in our Worm Casting Seedling Mix

To learn even more about how beneficial worm castings are to your plants, you can read our full Worm Castings 101 guide!

How much worm castings to use for starting seeds?

Rather than using a sterile store bought mix, incorporate some worm castings into your seed starting this season. There are two ways that you can go about this:

  • DIY: If you want to build your own seedling mix, you will want to add worm castings to an existing seed starting mix or potting mix. You want to aim for about 10-33% of the mixture to be worm castings and the remainder of the mixture being your potting mix (bonus points if you add sifted compost).
  • Worm Castings Seedling Mix: If you don't have the time to care for and harvest your own worm castings, then we can ship our Worm Casting Seedling Mix directly to your door! This is the exact mixture that we use to start all our seeds in and have had countless 5-star reviews of!

Image of seedlings growing much larger in Mind & Soil's Worm Casting Seedling Mix

Hundreds of happy customers have been starting seeds with our worm castings seedling mix and growing beautiful, strong seedlings!

Can worm castings burn seedlings?

No! You could start seeds in 100% worm castings and you are not at risk of those seeds being burnt. However, they will grow better in a mixture that contains a combination of worm castings, compost and a medium such as peat moss or coco coir.

Which worm castings are best?

The best worm castings are those coming straight out of your own worm farm! The reason being is because they will not only be the freshest but also because if you feed your kitchen scraps to the worms then they are getting a very diverse and nutritional food source. 

However, caring for a worm farm can be a lot of work and takes many hours. Because we might not all have the time, space, or energy for this, we created our Worm Casting Seedling Mix so you can get all the benefits of worm castings without any of the dirty work! We ship across all of Canada and you can grab your worm casting seedling mix here


  • Could you start seedlings in just a mix of worm castings and compost and some of the garden soil from your beds, or using such be harmful to the seedlings?

  • How to sprouting broccoli seeds in earth

    Sfey sfey Sr.

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