Crafting the Perfect Starting Mix for Seeds & Planting Success

A good seed starting mix is key for giving plants a strong start, but with so many choices, how do you know which is the best? They all claim to be ideal for starting seeds. As a beginner gardener, I found that overwhelming. In this post, let’s de-mystify what makes a great seed starting mix.

I’ll tell you how to make and use an easy DIY starting mix for seeds that can give your plants an amazing boost, help them grow healthy, and save you money.

Let’s grow bigger!

Why I Love Seed Starting

Never underestimate the power of planting a seed. Just one seed has the potential to produce so much food while providing even more seeds you can save to continue the cycle of abundance!

Starting your own seeds opens up a world of unique plant varieties and money-saving benefits to the home gardener. Plus, you get the satisfaction of enjoying fresh home-grown produce.

That’s why I’ve created this DIY Starting Mix for Seeds Guide and more guides with everything you need for successful seed starting:

• How to Start Seeds Indoors

• How to Make Soil Blocks

• When to Start Seeds Indoors

• Cold Stratification

• Winter Sowing

What is a Seed Starting Mix?

A seed starting mix is an ideal growing medium for the early stages of a plant's life. It's different from regular garden soil because it's finer and more sterile with additives that maintain moisture and aeration.

I recommend using a seed starting mix whenever you start seeds indoors. This mix recipe also works great for winter sowing outdoors in containers.

Pro-Tip: If you want to purchase bags of seed starting mix instead of making your own, I recommend either of these two quality options: Pro-Mix Premium Potting/Seed Starting Soil and Happy Frog Potting Soil by FoxFarm.

The Benefits of This Starting Mix Recipe

The DIY starting mix recipe that I use is coconut coir based. This mix is high quality and so easy to work with. I think you’ll love it as much as I do.

Seed Starting Containers and Trays

Plastic pots, cell plug tray inserts, and seed starting trays are used for indoor seed starting. These are great options, and I use them for my tomatoes and peppers every year.

You can also use a soil blocking tool to compress this mix into a firm block that will hold its shape just as if a plastic pot surrounded it. This allows seedlings to grow in soil cells where air pruning will create far healthier root systems.

Which Crops Benefit the Most from Indoor Seed Starting

Many plants benefit from indoor seed starting. The most popular crops to start indoors are tomatoes, peppers, onions, cucumbers, kale, cabbage, eggplant, and herbs like sage and basil.

Pro-Tip: Seeds that grow naturally in an area that experiences cold winter weather will often require cold stratification before starting indoors, especially if they are perennials.

Here are some excellent options to start indoors:

Some plants just need more space than indoor growing allows. Crops like beans, sunflowers, and squash grow best when directly sown outdoors.

How to Make a DIY Starting Mix for Seeds

Here is a step-by-step guide to make the perfect homemade mix for amazingly healthy plant starts. This recipe contains all the essentials needed in a quality seed starting mix.

Seed Starting Mix Ingredients

• Coco Coir - Coconut husk fiber is the main growing medium in this recipe. Pro-Tip: When purchasing coco coir, pay attention to the product's grade (or coarseness) and salt content. You do not want chipped shells or particulates in it. I recommend ultra-fine premium grade A compressed coco coir blocks that are already triple-washed to remove salt.

• Vermiculite - Vermiculite is critical in your seed starting mix. It is an expanded volcanic rock that is very porous, allowing it to hold onto water and nutrients so they don’t drain through the soil.

• Perlite - Perlite is an expanded volcanic glass used in high-quality seed starting mixes to prevent compaction and allow better drainage. There are different grades of perlite. I prefer using fine to medium perlite. Extra-fine will work, too, but you will need to add more of it.

• Water - Warm water works best and speeds up the process, but you can also use cold water if that is all you have available.

• Fertilizer - Most seed starting mixes do not contain fertilizer. Since we are making our own, we can add it right into the seed starting mix. Choose a well-balanced, slow-release fertilizer, such as Trifecta+ and/or a gentle fertilizer like worm castings.

Supplies Needed

• Trowel - A transplanting trowel works great to remove chunks of coco coir from the block.

• Container - You will need a container, like a plastic washtub, to hydrate the coconut coir and mix the ingredients in.

Step-by-Step Instructions

1. Open the Coco Coir - Open the package of coco coir.

2. Break Off Coco Coir From the Block - Take a trowel (or a screwdriver) and stick it into the side of the coco coir block, not the top or bottom, flaking off chunks until you break off the desired amount. Put the chunks into the washtub. Pro-Tip: Keep any unused coco coir dry in a bag so it will be good for next time.

3. Add Water - Hydrate the coco coir by adding warm water. Mix it with the trowel or your hands until it is moist and fluffy. Continue adding water until the coco coir is fully hydrated and has no dry spots.

4. Add Perlite - Add 10-15% perlite by volume. It is very dusty, so add it slowly and moisten it with water.

5. Add Vermiculite - Add vermiculite, about 10-15% by volume.

6. Add Fertilizer - Using the fertilizer of your choice, add it at a ratio of 3 Tbsp for every gallon of starting mix. (Optionally add 2 Tbsp of worm castings per gallon as well.) Pro-Tip: It is a common misconception that brand-new seedlings need fertilizer. They don’t. In their seed coat, the seeds have all the nutrients and energy needed to sprout. But once they start to form adult leaves, they DO need to start uptaking nutrients. Adding fertilizer now means it is available to the plants when they need it.

7. Mix the Ingredients - Slowly incorporate the ingredients with a trowel or your hands until it is thoroughly mixed.

8. Check the Moisture - If you take a handful of finished seed starting mix and squeeze it very hard, a few drops of water should come out. If not, add a bit more water.

To make a potting mix for container gardening instead of starting mix, simply increase the size of the perlite for better drainage and aeration.

How to Use Seed Starting Mix

Use this seed starting mix in any type of seed starting container or tray with the seeds of your choice. Simply fill your container with seed starting mix, and start sowing!

It is also perfect for container-less seed starting using soil blocks!

Check out this post on How to Start Seeds Indoors for information about grow lights, seed-starting heat mats, watering seedlings, and other seed starting tips.