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Help Your Seedlings THRIVE with These Seed Starter Mixes

Creating your own seed starter mix is a fantastic way to give your seedlings the best start in life. Plus, it’s fun and rewarding! Here are three of my favorite recipes to make your own seed-starting mix at home, so you can successfully start your seeds indoors and extend the harvest!

A pot slipping over with vermiculite, a bag of Hoffman's seed starter potting and plant mix, a bag of espoma brand organic perlite, with Marion Owen coming out of the right edge holding two thumbs up!

Before we get to the recipes, I wanted to talk about why we don’t use garden soil for starting seeds. Garden soil can be too dense and might not provide the right conditions for your delicate seedlings. So, while it might be tempting to just scoop some dirt from your garden, it’s better to use a specially prepared seed starter mix to give your seeds the best chance to thrive.

Many sources will tell you that garden soil harbors bacteria and fungi, which is true. However, adding garden soil to your seed-starting mix does not directly cause damping-off, a common issue for beginner gardeners’ seedlings.

In fact, recent studies show that incorporating garden soil or compost to a seed-starting or potting soil mix is beneficial for seedlings. According to my friend Jeff Lowenfels), known for having the longest-running garden column in North America and several bestselling books, including “Teaming With Microbes:

“When starting seeds and raising seedlings, use living soil, not sterile soil. The microbes in living soil are almost always diverse enough to keep the fungi that cause damping off in check.”

Preventing damping-off is discussed in further detail in another post: Prevent Leggy Seedlings With These Tips

Josh's Frogs vermiculite product photo from Amazon
Josh’s Frogs vermiculite product photo from Amazon

Recipe 1: Vermiculite Only

Let’s start with the simplest recipe: just vermiculite. Vermiculite is a natural occurring mineral that has been puffed up like popcorn, making it light and spongy. It’s the perfect growing medium for seed starting because it holds moisture well while still allowing for good drainage. Just fill your seed trays or pots with vermiculite, plant your seeds, and water them in.

Here’s my recommendation for vermiculite: Josh’s Frogs Vermiculite. The size of the particles makes this brand of vermiculite ideal for starting seeds. Clean, consistent texture and dust-free.

Two hands outreached holding foraged moss from the forest

Recipe 2: Vermiculite and Milled Sphagnum Moss

Next up, we add a little something extra: milled sphagnum moss. Sphagnum moss is another fantastic medium for seed starting because it’s lightweight and retains moisture really well. To make this mix, combine equal parts vermiculite and milled sphagnum moss. And here’s a fun tip: you can collect moss from the woods, dry it, and mill it in a food processor. It’s a bit of an adventure, but totally worth it!

Espoma brand organic perlite product photo from Amazon
Espoma brand organic perlite product photo from Amazon

Recipe 3: Vermiculite, Milled Sphagnum Moss, and Perlite

For the third recipe, we go all out by adding perlite to the mix. Perlite is another natural mineral that’s been puffed up like popcorn. It helps with drainage and keeps the mix light and airy. Combine equal parts vermiculite, milled sphagnum moss, and perlite. This mix doesn’t contain nutrients, so you’ll need to feed your seedlings regularly until they get their roots in real soil. (You can provide food in liquid form). It’s like hydroponic gardening, where the medium just holds the plants up while you provide the food.

Here’s my recommendation for perlite: Epsoma Organic Perlite. This perlite is just the right size (not too chunky) for DIY potting mixes or adding to garden soils or pre-mix potting mixes to improve drainage. Also good for starting cuttings.

Understanding Vermiculite and Perlite: Which Soil Amendment Should You Use?

Vermiculite and perlite are two common soil amendments that enhance drainage and aeration. While they may appear similar, they have some key differences:

Usage: Vermiculite is ideal for plants that need consistent moisture, while perlite suits those that prefer drier conditions. Perlite excels at improving soil drainage and aeration, whereas vermiculite is better at retaining moisture.

Material: Vermiculite is a naturally occurring mineral that is heated to expand into lightweight granules. Similarly, perlite is a natural mineral that expands when heated, resulting in lightweight, porous granules.

Water Retention: Vermiculite holds more water than perlite, capable of retaining three to four times its weight in moisture. It’s commonly used in mixes for moisture-loving plants. In contrast, perlite has a lower water retention capacity and is better for plants that thrive in drier soil.

Aeration: Perlite offers superior aeration, improving drainage and preventing waterlogging. It’s often included in soil mixes for plants that require good drainage and air circulation. Vermiculite, while less effective for drainage, is primarily used to enhance moisture retention.

pH Levels: Vermiculite has a neutral pH of around 7.0, while perlite has a slightly alkaline pH, ranging from 7.5 to 8.0.

What happens next?

Remember, these mixes are just the starting point. As your seedlings grow, they’ll need to be potted up into a richer mix. Seedlings truly benefit from a more complex interaction that takes place in real soil, so they should eventually be potted up to a richer mixture (compost is another good way to do this: Read the Beginner’s Guide to Compost to learn more!). 

But with these recipes, you’ll be well on your way to growing strong, healthy plants. 

Hoffman brand seed starter potting and planting mix product photo from Amazon
Hoffman brand seed starter potting and planting mix product photo from Amazon

Don’t want to make your own seed starter mix? You can buy premade mixes to help you out. My recommendation is Hoffman 30103 Seed Starter Soil. I’ve started thousands of seedlings over the years and Hoffman’s is my favorite. Compared to other brands, it has a fine consistency with very few twigs or bits of bark. It absorbs and holds water well. Ideal for starting seeds in containers or mini soil blockers.

Happy gardening!

About Marion

Learn the gentle art of nurturing your garden using simple organic methods like composting that have been field-tested for nearly 40 years by Marion Owen, New York Times bestselling author.