Use the Right Mix for Indoor Seed Starting

A seed starting mix is not the same thing as your regular ol' potting soil. If you plan to start seeds indoors, it's important to buy the right kind of growing medium so that you can encourage germination and root growth. Of course, there are all kinds of different recipes out there to make your own seed starting mix, but the simplest way to get started is to buy an organic bag that's (almost) ready to go.

Seed Starting Mix vs Potting Soil

Seed starting mix is a bit finer and lighter than regular potting soil or topsoil. This ensures there are lots of little air pockets so that your tender baby plants can push their roots into the medium when they first break free from the seed and begin to grow. You wouldn't want to start seeds in something as dense as potting soil or topsoil because that could impede those little roots.

A seed starting mix also really needs to be able to retain moisture, since water is the primary element that wakes a seed up from its dormancy and encourages it to sprout. Unlike potting soil, seed starting mixes don't need to provide a ton of nutrients to the seedling, since seeds contain all the nutrients the plant needs to begin its life cycle. No fertilizer required. No compost required.

Seeds are pretty magical, y'all. If you've never watched a seed grow into a plant before, you're in for the best show of your life!

What's Inside a Seed Starting Mix?

Most seed starting blends include at least some of the following ingredients:

• peat moss to retain moisture
• vermiculite to help aerate the mix
• perlite to keep the mix light
• mycorrhizae to promote root growth
• coco coir to retain moisture and aerate mix
• compost to feed seedlings as they grow
• fertilizer or small quantities of nutrient starters such as kelp meal and worm castings
• lime to balance the pH

When combined in the right amounts, these ingredients should nurture vigorous seedlings with strong root systems that are capable of withstanding the transplanting process outdoors and then thriving in the kitchen garden all season long.

Note: I generally try to stay away from peat moss and other nonrenewable resources due to their lack of sustainability, but peat is still a really popular ingredient for seed starting mixes. A good alternative to look for is a mix with coco coir, which is made from coconut fiber.

Organic seed starting mixes should be sterile to reduce the presence of pathogens like fungal spores and other things that you don't want growing inside these little cells (like bugs... yuck!). Pathogens can cause damping off, a disease that weakens or kills seedlings after germination, especially when conditions are too wet or cool.

My Favorite Seed Starting Mix Options

The easiest way to get started is to buy an organic seed starting mix from the store. Each bag should produce enough mix to fill two to three seed starting trays, depending on the size of your trays, of course.

(By the way, some of the links in this article are Amazon affiliate links, which means I receive a small commission at no extra cost to you if you click on the link and purchase the item.)

Here are some of my favorite options available on Amazon:

• Jiffy Natural & Organic Starter Mix (12-quart bag, $19.99)
• SunGro Horticulture Black Gold Seedling Mix (8-quart bag, $17.48)
• Coast of Maine Organic Seed Starter Blend (8-quart bag, $22.99; I recommend getting 2 bags for $30.58—a great deal!)
• Purple Cow Organics All-Natural Seed Starter Mix (12-quart bag, $24.49)
• Espoma Organic Seed Starter (8-quart bag, $24.85)

If you don't want to shop online, consider stopping by your local nursery or garden center to find an organic seed starting mix recommended by growers near you. Check for the OMRI badge, which means the product has been reviewed and found acceptable for certified organic production.

Bonus Option: A Coco Coir Seed Starting Brick

Coco coir bricks are relatively new to me, but I really like how each brick comes with minimal plastic packaging. A coco coir brick is basically like those magic sponges that expand in water we played with as kids. It arrives in the form of a one-pound brick made of compressed coco coir, and you add water over it in a bucket and then allow the brick time to fully swell and break apart.

The brick that I expand in the video below is from Burpee, and you can find a two-pack here. It's 100 percent biodegradable and made from plants. I thoroughly enjoyed watching my little brick expand into a wonderfully light and fluffy growing medium for all my seeds.

How to Make Your Own Seed Starting Mix

If you’re looking for a budget option, rather than skimp and buy a non-organic mix (which might contain chemicals or synthetic agents), make your own. Combine compost, topsoil, a bit of coarse sand, and something like vermiculite, perlite, or coco coir until you have a mix with a consistency that holds together when wet. 

For seed starting, you'll avoid using as much sand as you would when making soil for your garden. The ideal seed starting mix consistency will hold together better than the soil you'd use in your garden when wet.

Indoor Seed Starting Tips

You might notice how easy it is to carry a bag of seed starting mix versus potting soil, and when you open your seed starting mix, you'll see why. The medium inside should feel so light and fluffy and dry.

And that's because it's been dehydrated for easier transportation. Remember, it's water that wakes your seeds up from their dormancy, so it's critical to properly prepare your seed starting mix first by adding water and rehydrating it.

In a large mixing bowl, combine about 3 cups of water at a time into your mix. You'll notice that the mix is almost hydrophobic, so you'll need to mix it with your hands to really saturate it. (I make a huge mess doing this, so be warned!) The ideal consistency is a mixture that holds together without dripping too much when you scoop up a handful and squeeze it between your fingers. (If you're going to use the mix for seed blocking, then you do want it to be a little on the wetter side and drip through your fingertips.)

I recommend rehydrating your mix a couple of hours before you're going to plant out your seeds so that it has time to settle a bit. (You can watch me rehydrate a mix in the video below.)

For more indoor seed starting tips, check out our Seed Starting course inside of Gardenary 365. We've got video lessons to walk you step by step through selecting the right supplies for your needs, planting out your seeds in the trays, and helping them grow. We'll also help you troubleshoot common seed starting issues.

Tis the Season for Indoor Seed Starting

Starting your own seeds indoors can be a commitment. It took me several seasons to gather the right supplies, figure out the best setup, and master this skill. I recommend grabbing one of these top organic seed starting mixes and then giving yourself lots of grace as you start seeds for the next couple of growing seasons.

If you're still looking for the best trays and grow lights for seed starting indoors, check out my top picks on Amazon.

Thanks for helping make gardening feel ordinary again, and best of luck to you as you start your seeds!