What Is Seed Starting Mix? (5 Key Ingredients To Know)

If you are starting plants from seed, it makes sense to ask what seed starting mix is, what it is made from – and if you even need it.

So, what is seed starting mix?  Seed starting mix is a blend that helps seeds to germinate. It retains water and air to keep seeds alive – and it is ideally sterile to avoid disease. Seed starting mix is often made from peat moss, coconut fiber, perlite, vermiculite, and possibly some nutrients to help seedlings continue growing.

Without seed starting mix, you will still get some seeds to sprout – but problems with disease or moisture will often reduce your germination rate. If you would rather not waste seeds, you can learn more about seed starting mix below.

In this article, we’ll talk about seed starting mix and why it is so important. We’ll also talk about where you can find seed starting mix and how to make your own.

Let’s get started.

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What Is Seed Starting Mix?

Seed starting mix is a special blend made from several different ingredients. This mixture provides the ideal environment for seeds, helping them to germinate faster and at a higher success rate.

tomato seedling
Seed starting mix gives you a higher germination rate and healthier seedlings.

Seed starting mix retains water – enough to encourage germination, but not enough to drown them. It also retains air, which is necessary so that seeds can “breathe”.

Seeds are susceptible to pests and diseases. For this reason, seed starting mix is also sterile (so avoid fresh manure or garden soil that may contain insects, pathogens, seeds from weeds, etc.)

Seed starting mix is made from a blend of various materials, including:

  • peat moss
  • coconut fiber
  • perlite
  • vermiculite
  • possibly some compost (as long as it is sterile, meaning it got up to 130 to 160 degrees Fahrenheit).
  • possibly some fertilizer (adds nutrientsto help seedlings continue growing after germination)
sphagnum peat moss
Peat moss is one common ingredient of seed starting mix.
Image courtesy of:
Ragesoss via Wikimedia Commons: https://commons.

The question remains, though: do you really need to use seed starting mix at all? Or is it just hype?

Is Seed Starting Mix Necessary?

Strictly speaking, seed starting mix is not necessary. However, it is highly recommended by lots of gardeners, including me (don’t take my word for it, though!)

seed tray
Seed starting mix is often used in seed trays to control moisture levels, avoid pests, and prevent diseases.

Using a seed starting mix has the following benefits over ordinary soil:

  • Maintains moisture levels when wet (not dusty and dry, but not soggy and wet)
  • Retains air (which seeds also need to germinate)
  • Lighter than soil (prevents compaction and avoids drowning or suffocating seeds)
  • Sterile mix (reduces the chance of pests, diseases, and weeds)

This last point is especially important for several reasons. For one, it is easy to lose seedlings to diseases or insects before they are well-established.

It is also important to use a sterile mix because disease in one seedling (or tray) can easily spread to others. If you spend a little time making sure you have a clean growing medium, you will save your seedlings from an early demise!

damping off seedling
Damping off of seedlings is more likely if you use garden soil instead of seed starting mix.
Image courtesy of:
INAKAvillage211 from:

Keep in mind that seed starting mixes vary in terms of nutrient content. Some seed starting mixes have no added nutrients at all. If you use one of these, you will need to fertilize seedlings after they emerge (don’t overdo it – it is possible to over fertilize plants, including young ones!)

Other seed starting mixes add varying levels of nutrients. Some can provide young plants with enough nutrients to keep them growing for weeks or months!

Either way, check the label so you know for sure. If you need to add nutrients, make a note of it so you don’t forget (your seedlings will probably remind you at some point!)

Some seed starting mixes have added nutrients to help plants continue growing weeks or months after germination.

As you can see, seed starting mix offers many benefits over other growing media. However, you might still want to start seeds in garden soil, potting soil, or another such growing medium. Just remember that this can lead to problems.

Can You Start Seeds In Any Soil?

You can start seeds in any soil you like, but you might not like the results! Seed starting mix and garden soil are not the same thing.

Garden soil is not the same as seed starting mix – so you might not get the same results when sowing seeds!

According to the University of Illinois Extension, ordinary garden soil might have seeds of other plants, which will compete with the ones you are sowing.

Garden soil is also denser than seed starting mix, making drainage difficult (especially if you over water by mistake).

There are numerous risks to planting seeds in soil instead of a seed starting mix:

  • Sandy soil – this soil has large, coarse particles. It tends to drain fast and dry out. If you don’t keep an eye on soil moisture, you will see slow germination or low germination rates – and your seeds might even die.
  • Clay soil – this soil has small, fine particles. It tends to drain slow and stay wet. If you over water this type of soil, your seeds will drown or rot, due to a lack of air.
  • Garden soil – this soil is more likely to have pests (like insects) that might want to feed on your seeds. It is also more likely to have pathogens (like mold, bacteria, and viruses that cause plant diseases). This is especially true if you had a problem with diseases in your garden before.
clay soil
Clay soil retains water and stays wet, posing the danger of drowning seeds before they germinate.

Is Seed Starting Mix The Same As Potting Soil?

Seed starting mix is not the same as potting soil. Although you can use potting soil to start seeds, it is often a little heavier than seed starting mix. Both might have fertilizer added, depending on the brand and mix.

Potting mix often contains garden soil, finished compost, or aged manure (hopefully sterile!), which does add some nutrients. This means that you won’t have to worry as much about adding nutrients to a potting mix.

repotting plant
Potting soil is often used to pot or repot houseplants. It is denser than seed starting mix.

You also have the option to begin by sowing seeds in a tray filled with seed starting mix. Then, after the seedlings emerge and grow a bit, you can repot (pot up) each plant to a larger individual container.

This new container can contain some potting mix, which has more nutrients to help with continued growth.

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What Can I Use Instead Of Seed Starting Mix?

As mentioned before, you can use potting mix or soil instead of seed starting mix. However, potting soil is a little denser than seed starting mix, and garden soil might have diseases or insects.

Perlite is one key ingredient of many seed starting mixes.

You can buy seed starting mix and other growing media from True Leaf Market.

If you don’t want to buy a seed starting mix, you can make your own. However, you will still have to buy your own materials – and you might need to buy in bulk to make it worth your while. Maybe you can share with family, friends, and neighbors!

How To Make Your Own Seed Starting Mix

To make a seed starting mix, you will need two basic ingredients:

  • Peat moss or coconut fiber – these gives your mix a “soil-like” consistency, without the density of actual garden soil (topsoil).
  • Perlite or vermiculite – these helps your mix to retain both water and air. Retaining enough water (but not too much) encourages seeds to germinate without drowning them.
coco coir coconut fiber mat
Coconut fiber (coco coir) is often used in place of peat moss in seed starting mix.

In addition to these two basic ingredients, you can choose from various additives to add nutrients to your mix. If you don’t add nutrients, make sure to fertilize after the seeds germinate, or else transplant them into a mix that already has nutrients.

If you choose to add finished compost or aged manure to your mix, do everything you can to ensure they are sterile (clean). This is a move that reduces the cost of your mix, but increases the chance of disease.

A good cheap “filler” alternative is sand – but this makes your mix drain faster (so be careful it doesn’t dry out).

See the recipes below to find out how to mix these ingredients.

Seed Starting Mix Recipes

Here are a few recipes for seed starting mix to give you an idea of how to make it.

Peat-Perlite: basic mix with only two ingredients; 75% peat moss.

  • 3 parts peat moss
  • 1 part perlite

Sand-Peat-Perlite: equal parts perlite & sand; 75% peat moss.

  • 6 parts peat moss
  • 1 part perlite
  • 1 part sand

Compost-Peat-Perlite: put some of your compost to good use!

  • 1 part sterilized compost
  • 1 part peat moss
  • 1 part perlite

You can follow the above recipes to the letter, or you can switch it up a bit.

For example, to modify the first recipe, you can switch out perlite for vermiculite if you want your mix to retain more water, use:

  • 3 parts peat moss
  • 1 part vermiculite

Or, you can use coconut fiber instead of peat moss:

  • 3 parts coconut fiber
  • 1 part perlite

Or, you can use half perlite, half vermiculite:

  • 6 parts peat moss
  • 1 part perlite
  • 1 part vermiculite

Experiment to see what you like best (but the most important thing is what the seeds like!)

If you want to add nutrients, you can try:

nitrogen (N) – add some to your mix with:

  • blood meal
  • feather meal
  • fish/crab meal
Feather meal is one source of nitrogen for plants.

phosphorus (P) – add some to your mix with:

  • rock phosphate powder
  • bone meal
  • fish meal (or emulsion)
bone meal
Bone meal is a source of phosphorus for plants.
Image from: https://commons.wikimedia.org/wiki/File:%D0%93%D0%BE%D1%80%D1%81%D1%82%D1%8C_%D0%BA%D0%BE%D1%81%D1%82%D0%BD%D0%BE%D0%B9_%D0%BC%D1%83%D0%BA%D0%B8_2014-05-07_13-57.jpg

potassium (K) – add some to your mix with:

  • kelp/seaweed (or an extract)
  • wood ash
  • greensand
Kelp or seaweed adds potassium to your mix.

calcium (Ca) – add some to your mix with:

  • lime
  • dolomite lime (also adds magnesium)
  • gypsum (also adds sulfur
  • wood ash
  • bone meal
Lime (calcium carbonate) adds calcium to your mix.

magnesium (Mg) – add some to your mix with:

  • dolomite lime (also adds calcium)
  • Epsom salt (also adds sulfur)
  • sulfate of potash magnesia (also called Sul-Po-Mag)
  • wood ash (has a small amount of magnesium)
magnesium sulfate epsom salt
Epsom salt adds magnesium to your mix.

sulfur (S) – add some to your mix with:

  • gypsum (also adds calcium, and is pH-neutral)
  • Epsom salt (also adds magnesium)
  • elemental sulfur (careful – this makes soil more acidic!)
Gypsum adds sulfur to your mix.


Now you know what seed starting mix is and why it is helpful to use it when growing plants from seed. You also know where to find seed starting mix and how to make your own.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

Check out this article that will help you to figure out how many seeds to plant.

You can learn how to save seeds from your garden here.

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Jon M

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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