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Seedling Soil: Everything You Need to Know

Did you know – what your seeds are planted in will directly affect their growth and health? Soil is what allows hydration and passes on nutrients to roots. Without good soil, plants will never see their full potential.

The same can be said for seedlings. It’s important to pick the right seedling soil. The first few weeks of growth are what determine whether a seedling will make it or not.

In this post, I’ll go over all you need to know about seedling soil. That includes – what should be in it, where to get it, and even how to make your own.

Keep reading for more!

Cherry tomato seedlings in seedling soil.

What Is the Purpose of Seedling Soil?


Indoor seed starting is much different than gardening outdoors. Your seedlings will grow in a small cell that is approximately two inches wide. And, since there is no wind, seedlings don’t typically dry out as quickly as outdoor plants.

That’s why it’s imperative that seedling soil have good drainage. Seedlings shouldn’t sit in soggy soil, as it will stunt growth and invite mold.

Seedling soil is made of light ingredients that hold just enough water, but still allow drainage. Examples of these ingredients (which I’ll talk about in more detail) are peat moss, vermiculite, perlite, and coconut coir.

Root Formation

Another perk of light ingredients is easy root formation. Small seedlings have to form roots to attain healthy growth.

Closeup of celery seedlings in seed starting mix.

These small roots aren’t able to work around large pieces of soil. Therefore, seedling soil must be made of fine, sifted ingredients.

While you might find chunks of bark or compost in regular soil, seedling soil should be the opposite. Most seedling soil is poured through a sifter before being bagged and sent out.

Nutrient-Less Ingredients

Ingredients in seedling soil should contain little to no nutrients. After plants are established in the garden, added nutrients are a great thing. But, added nutrients or fertilizer at the seedling stage will only overwhelm seedlings.

The main purpose of seed starting mix is healthy root formation. Seedlings will be able to develop adequate foliage even without nutrients at this point. All they really need is water, light, the correct temperature, and good drainage.

Some seedling soils do have some nutrients added, such as compost or worm castings. These are fine in moderation but should be used lightly.

Seedling Soil vs. Potting Soil

So, what’s the big difference between seedling soil and potting soil? Is it possible to use both interchangeably?

There’s actually quite a distinction between the two. Despite the name, seedling soil doesn’t contain soil, and you’ll see it most often referred to as seed starting mix. Potting soil, on the other hand, does contain soil.

A pepper seed in seedling soil.

Seedling soil is made from no-frill, natural ingredients that retain moisture while aiding in drainage.

In contrast, potting soil is composed of different added nutrients along with soil and compost. This is pertinent for plants to be able to form large, healthy fruits.

When is it appropriate to use seedling soil versus potting soil?

Seedling soil should be reserved for starting seeds only. Because it doesn’t contain nutrients, adult plants will struggle to get enough energy for foliage and fruit development.

And honestly, it’d be more expensive to use seed starting mix as potting soil. This is because you’d have to supplement with fertilizer frequently.

Vice versa, potting soil shouldn’t be used when starting seeds. The ingredients could be overwhelming to young seedlings, and potting soils often contain large, unsifted ingredients. This can lead to air pockets and poor root development.

A container of potting soil showing the size of ingredients.
Potting soil.

For more information on the difference between seed starting mix and potting soil, visit this post.

What Should Be in Seedling Soil

There are some common ingredients that you’ll see in most seedling mixes. Let’s go over the top four.

Sphagnum Peat Moss

Person holding handful of peat moss.

Sphagnum peat moss is the most commonly used ingredient in seedling soil, as it acts as the “soil”. It is a lightweight, spongey ingredient that drains well, but doesn’t dry out too quickly.

Sphagnum peat moss is actually the result of sphagnum moss that has broken down over hundreds, even thousands, of years. It primarily originates from peat bogs in Canada. Here, they harvest the peat moss in bulk, ready for sale.

So, technically peat moss is just decomposed matter – not soil, at all!

It’s a cost-friendly ingredient if you purchase it individually, running around $15 per 10 quarts.

Coconut Coir

Person holding handful of coconut coir.

Coconut coir is an eco-friendly alternative to sphagnum peat moss. You may be wondering, “Why isn’t peat moss eco-friendly?”

Sphagnum peat moss releases carbon dioxide when harvested, which can be a lot when harvested in bulk. Some gardeners choose not to use it because of that reason.

Coconut coir is made from the interwoven threads that exist between the outer husk and the meat of a coconut.

Coconut coir is very absorbent and has a similar texture to peat moss. It also allows good airflow around seedling roots without drying out easily.

Coconut coir is sold in dehydrated bricks, and it is just as affordable as peat moss. So, it really doesn’t make a difference price-wise whether you go with peat moss or coconut coir.


Person holding handful of perlite.

Perlite is another common ingredient in seedling soil. Perlite is a mineral mined from volcanic glass/rock, and it resembles small, white beads.

It easily retains water, while breaking up other ingredients for optimal airflow. If you have a history of waterlogged seedlings, perlite could be your answer.

It’s also extremely lightweight, so it’s perfect for seedling mixes. Perlite is treated with heat to expand it, so it’s non-toxic and organic.


Person handful of vermiculite.

Vermiculite is very similar to perlite, but it is more water-absorbent than perlite. Vermiculite is mined from the ground, and it is treated with heat just like perlite. This makes it sterile and non-toxic.

Vermiculite is a great additive to keep soil from getting compacted or waterlogged. It breaks up soil and helps with airflow.

Vermiculite and perlite are usually added in smaller proportions than peat moss or coconut coir. But, they usually come in similar size bags for the same price. Therefore, you can get a good bit of this ingredient for a reasonable price.

Where to Get Seedling Soil

Seedling soil is widely sold on gardening websites such as Hoss ToolsTrue Leaf Market, or even Amazon. You can also usually find it in person at your local garden center or nursery.

Here is a quick list of my three favorite seedling soils:

Hoss Premium Seed Starting Mix

Hoss’ seed starting mix is packed full of soil-less ingredients. Coconut husk peat, perlite, worm castings, and greensand are just a few. It’s a natural, lightweight mix to get your seedlings off to a good start.

Hoss Tools' seed starting mix.

Sungro Black Gold Seed Starting Mix

Sungro’s Black Gold mix is a simple combination of sphagnum peat moss, perlite, and dolomite lime. It’s also double-sifted, so you don’t have to worry about large pieces of soil. This is an ideal mix for root formation.

Sungro seedling mix.

Miracle-Gro Seed Starting Mix

Miracle-Gro’s Seed Starting Mix is a budget-friendly choice for seed starting mix. It does contain plant food, which I normally don’t recommend. But, it’s a very small amount, and the mix has overall great reviews.

Miracle-Gro Seed Starting Potting Mix, 2-pack 8 qt., For Use in Containers

For more information about seed-starting mixes for indoor gardening, read our post on our recommendations for Best Seed Starting Mixes.

Creating Your Own Seedling Soil

Ingredients for seedling mix.

You don’t have to rely on gardening websites and stores for your seedling starting mix. Why not try your hand at making your own?

Creating your own seedling soil is a great option for organic gardeners. You’ll be in control of what exactly goes into the seed starting mix. There’s no mystery, and you won’t have to decipher the small print of store-bought mixes.

It’s also a good way to save money in the long run. You’re paying a little more upfront to purchase all the ingredients. But in the end, you’ll be able to create a lot more seedling soil than what comes in a standard bag.

For the most basic seed-starting recipe, combine:

  • One to two parts sphagnum peat moss (or coconut coir)
  • One part vermiculite
  • One part perlite

Make sure to sift all your ingredients to ensure the finest mix. You can purchase a soil sifter from Amazon, or you can also use chicken wire or a metal grate.

Once you’ve combined everything, slowly add water to moisten the mix. Then, you’re ready to begin filling your seed starting trays!

Frequently Asked Questions

Seeds on starter tray cells of seedling soil.

1. How much seedling soil will I need?

To determine how much seedling soil you will need, take a look at how many seeds you plan on starting. An eight-quart bag will usually fill 100 to 150 standard-size cells. This is normally enough if you have a small garden.

But, you may want to invest in more seed starting mix if you will be potting up seedlings. This goes for fast-growing vegetables that quickly outgrow a regular cell before it’s time for transplant.

2. Will seeds germinate in potting soil?

Yes, you can successfully germinate seeds in potting soil. Even though it’s not recommended, there’s no rule against it. If it’s all you have available, there’s nothing wrong with giving it a shot!

There’s a chance it may overwhelm your seedlings if the potting mix is full of fertilizer and add-ins though. Sift out large pieces to help seedlings sprout up and form roots.

3. What are the best trays to use with seedling soil?

You can use any kind of seed starting tray with your seed starting mix. There are many different kinds and sizes. You can find them made of plastic, rubber, and biodegradable paper.

I recommend using reusable seed starting trays. You can toss them in the dishwasher at the end of the season and have them ready for next year. These are usually made of sturdier materials, as well.

For more information, take a look at the best seed starting trays for indoor gardeners.

Wrapping Up What to Know About Seedling Soil

A newly sprouted runner bean seedling.

Utilizing seedling soil will give you healthy seedlings with strong roots. Whether you purchase it from the store or create your own, you’ll notice the difference in how your seedlings thrive.

For more information on getting your garden started, be sure to visit our Seed Starting page on the website. We’ll take you through how to grow your favorite vegetables, along with the best products to accomplish it.

Shopping for your garden can get overwhelming, fast. So if you’re looking for advice on garden tools and garden supplies, then you’re in the right place! And if you’re looking for a unique gift for a loved one, how about a gardening gift?