DIY Seed Starting Mix: Easy Coco Coir Recipe

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When it comes to starting seeds, I like to keep things as natural and hands-on as possible. Instead of buying pre-blocked trays of seed starting mix, I prefer to soil block my own. Not only does this save money, but it also gives me full control over what goes into my soil—something I find incredibly important for healthy, strong seedlings.

One of my favorite ingredients for a good seed starting mix is coconut coir. If you’ve read my previous article on coco coir, you already know how much I love using it as a sustainable alternative to peat moss. It retains moisture beautifully, provides excellent aeration, and helps create the perfect texture for seed-starting.

Over the years, I’ve fine-tuned my own DIY seed starting mix recipe that works wonderfully for soil blocking. It’s light, fluffy, and holds just the right amount of moisture without becoming waterlogged. Plus, I add my own homemade seedling fertilizer (which I’ll be sharing in another post soon!) to ensure my plants get the nutrients they need right from the start.

In this article, I’ll walk you through my step-by-step recipe so you can make your own DIY coco coir seed starting mix—perfect for soil blocking and giving your seedlings the best possible start!

Why I Use Coco Coir in My Seed Starting Mix

Over the years, I’ve experimented with different ingredients for my seed starting mix, but I always come back to coco coir as the base. It’s a fantastic alternative to peat moss, which I try to avoid because of its environmental impact. If you’ve read my previous article on coco coir, you already know why I love it—it’s sustainable, retains moisture beautifully, and promotes healthy root growth.

One of the biggest advantages of using coco coir in a seed starting mix is its ability to hold just the right amount of water while still allowing for proper drainage. Young seedlings are particularly sensitive to overwatering, and this mix helps prevent soggy conditions that can lead to damping off or root rot.

Another reason I rely on coco coir is its texture. It’s light and airy, making it easy to work with when creating soil blocks. Unlike some heavier mixes that can become compacted, this one stays fluffy and allows seedlings to develop strong, healthy roots. Plus, since coco coir is a neutral medium, I can customize the nutrient levels by adding compost and my own homemade fertilizer (which I’ll be sharing soon!).

By using coco coir as the foundation of my DIY seed starting mix, I know my seedlings are getting the best possible start. And the best part? It’s incredibly easy to mix up a batch at home! In the next section, I’ll go over all the ingredients you’ll need to make your own.

Ingredients for My DIY Seed Starting Mix

Making your own seed starting mix at home is simple, especially when you have the right ingredients. I’ve fine-tuned this recipe to create the perfect balance of moisture retention, aeration, and nutrients—everything seedlings need to develop strong roots and healthy growth.

Here’s what you’ll need:

2 – 1lb blocks of coconut coir + water – The foundation of this mix. Once hydrated, coco coir expands into a light, fluffy medium that holds moisture without becoming compacted.
2 gallons compost (32 cups) – Compost adds organic matter and beneficial microbes, giving seedlings a natural boost of nutrients. You can use homemade compost, high-quality bagged compost, or worm castings.
6 cups vermiculite – Helps with moisture retention, ensuring seedlings stay evenly hydrated.
6 cups perlite – Improves drainage and aeration, preventing the mix from becoming too dense.
2/3 cups seedling fertilizer – I use my own homemade fertilizer to give young plants the nutrients they need from the start.

This combination creates a lightweight, well-draining, and nutrient-rich seed starting mix that’s perfect for soil blocking. The coco coir and vermiculite keep moisture levels steady, while the perlite prevents compaction, giving roots plenty of space to grow.

Step-by-Step: How I Make My Seed Starting Mix

Once you have all your ingredients gathered, mixing up a batch of this seed starting mix is quick and easy. During the nice weather, I love using a wheelbarrow to mix everything up outdoors—it gives me plenty of space to work and keeps the mess outside. But since I’m working indoors during the winter, I use large plastic totes instead. They’re perfect for containing the mix and make cleanup much easier.

Here’s how I put everything together:

1. Hydrate the Coconut Coir

If you’re using a compressed block of coco coir, you’ll need to rehydrate it first. Place the 2 -1lb blocks in a large container (or directly in your wheelbarrow/tote) and slowly add warm water while breaking it apart with your hands or a garden trowel. Keep adding water and fluffing it until the coir is light, loose, and evenly moist—similar to the texture of damp soil.

2. Add the Compost

Next, I add 2 gallons of compost, mixing it in thoroughly with the coco coir. Compost provides essential nutrients and beneficial microbes that help seedlings get a healthy start. I like using my own compost when I have it, but high-quality bagged compost works well too.

3. Mix in the Perlite and Vermiculite

Now it’s time to add 6 cups of perlite and 6 cups of vermiculite. The perlite ensures good drainage, so the soil doesn’t get too compacted, while the vermiculite helps retain moisture. I like to mix these in gradually, stirring everything together to make sure they’re evenly distributed.

4. Add Fertilizer for a Nutrient Boost

The final step is mixing in 2/3 cups of seedling fertilizer. I use my own homemade fertilizer because I like knowing exactly what’s going into my soil. This gives seedlings a gentle but steady source of nutrients as they grow.

5. Store or Use Right Away

At this point, the seed starting mix is ready to use! If I’m making a batch for later, I store it in a sealed tote to keep it fresh. This mix is perfect for soil blocking, but it can also be used in seed trays or small pots.

And the best part? You can double, triple, or even quadruple this recipe depending on how much mix you need. I often make a big batch at the beginning of the season, so I have plenty on hand when it’s time to start new seeds.