Homemade Seed Starting Mix

Making a homemade seed starting mix is quite easy and can save you a ton of money. Especially if you plan on using a lot of it this year!

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Late winter and early spring are the perfect time to get your vegetable and flower seedlings planted. Over the years I’ve had many students ask me about using store-bought or homemade seed starting mix. This article will talk about the differences and help you decide if you should make your own seed-starter mix. I will also give you an easy recipe to follow to make your own.

What is seed starting mix & why is it important?

You may wonder why you even need to use seed starter mix? Wouldn’t it be easier to just use soil from the garden, that’s where the plants will end up eventually anyway?

Good garden soil is a mix of sand, clay, and silt along with a wide variety of organic material, fungal and bacterial life. When out in nature your garden soil is able to maintain a good balance between all of the good and bad bacteria. Also, the soil being part of a larger ecosystem keeps it balanced in its structure and texture.

If you bring garden soil inside and stuff it in tiny 1-3 inch pots all of the bad aspects of the soil will spring to life including overgrowth of bad bacterias and fungi. Also when you put garden soil in a small pot it quickly compacts and hardens. All of these factors lead to disaster for new seedlings.

Seed Starting Mix

Seed starting mix on the other hand is usually fairly free of bacteria and fungi and is made from ingredients that keep it lightweight, fluffy, and well-drained. This makes it easy for the new seedlings to build big, strong root systems.

Seed starting mix is usually called “soil-less” meaning it doesn’t have any real soil and instead is made of peat moss (or coco coir), pearlite, and vermiculite.

What is the difference between potting mix and seed starting mix?

Potting soil is usually meant for longer-term use in larger pots to support long-term plant growth. Potting mixes usually contain compost and fertilizers and also contain larger pieces of plant material like wood chips to help keep the soil structure open and light. They will also often contain some topsoil. All of these ingredients mean there will also be more chance of disease and fungal problems and weed seeds, new seedlings don’t need that!

Potting mixes don’t work as well for seedlings because they contain so much more rough material and are heavier than seed starting mixes. This limits the growth of those young new roots. Remember for new seedlings we want lightweight fluffy soil that will be easy for root growth.

Making Homemade Seed Starter Mix

The advantages and disadvantages of store-bought mixes

Of course, you don’t have to make your own seed starting soil, there are many seed starting mixes available commercially that will work perfectly. And I often use store-bought mixes.
The main advantage of a store-bought seed starting mix is convenience. It’s great to just stop by the local nursery and grab a bag to use. And as long as you choose an organic seed starting soil I don’t really have a problem with that.
But there are a few disadvantages to store-bought seedling mix.

Cost

An 8-quart bag of a quality organic seed starting mix will be around $8 or $10 (US). Making your own seed starting soil will have a larger upfront cost (you need to buy a large bag of each ingredient).
But when you break the cost down by what you need for 8 quarts of seed starting soil the cost of store-bought mix is 4 to 6 times what it costs to make your own. This can be a big saving when you grow a lot of seedlings.

Unneeded Ingredients

A seed contains everything a new plant needs for its first few weeks of life. Many commercial seed starting mixes contain compost, slow-release fertilizers, and other ingredients to “help your plants grow”.

But seedling mixes are meant to get your seedlings off to an amazing start, we add the other things the plants need to grow later. So these other ingredients in store-bought seedling mixes are not necessary and could even be detrimental to early plant growth.

Seed Starting Mix Ingredients

Before I give you the DIY recipe, let’s talk about ingredients. The best seed starting mixes call for 3 things, peat moss, vermiculite, and perlite. You will also sometimes see a recipe calling for coconut coir which is very similar to peat moss.

Peat Moss

Sphagnum peat moss is usually sold in large “bricks” that are packed solid with the material. A brick of peat moss can last you quite a few years. Peat moss gives your homemade seedling soil mix structure and water holding capacity without becoming waterlogged.

Peat moss is “mined” from bogs, mostly in Canada (in North America). Technically peat moss will eventually replenish itself, but this is a very long process so peat moss is generally not considered a sustainable or renewable resource.

Peat moss is a little acidic, some experts recommend adding a little lime to your seedling mix to balance out the ph, but I haven’t ever found this to be needed.

Coco Coir (Peat)

Coco coir is a by-product of the coconut industry. It is made from the material that sits between the hard outer shell and the soft inner “meat” of a coconut. In seed starting mixes it behaves almost exactly like peat moss.

Because it is made from a by-product it is generally considered “greener” than peat moss and more sustainable. There is still some debate about this in the “green” world because quite a bit of processing needs to happen to get the coco coir that we use. But most people agree that coco coir is overall a more sustainable option for making seed starting soil.

Vermiculite

Vermiculite is used for its high water holding capacity. This heated mineral looks a lot like mica and is used in small amounts in homemade seed starter soil mixes to help moisture retention. When you are working with vermiculite it is a good idea to wear a mask as it can be a lung irritant.

Perlite

Perlite is basically a volcanic glass that has been heated and “popped”. We use it in our homemade seedling soil mixes to add structure to the soil and to prevent it from compacting too much.

Seed Starting Mix Recipe

Before we start let me give you a couple of warnings. When mixing or handling seed starting mix you should wear gloves and wash your hands well after you are done. It is also a good idea to wear a dust mask when working with a dry seed starter mix.

A quick google search will show you a bunch of different ratios and recipes to use for your seed starting mix. Some will even include some compost. But the general recipe is between 60 to 80% Peat moss (or coco coir) with 10% perlite and 10% vermiculite. So here’s my recipe

Recipe

7 Parts Peat Moss or Coco Coir (your choice)
1 Part Perlite
1 Part Vermiculite

** What is a Part? This is any measurement you choose. If you are making a small batch the “part” could be just a cup. With a larger batch, you should be using a gallon bucket. The key is to get the ratio correct.

Place the ingredients into a large bin and mix well by hand or with a garden trowel. Adding water before use is important.

Peat moss and coco coir take a little effort to hydrate. It is very hard to get an even amount of moisture into your seed starting mix if you put it into your containers dry.

So instead pre-moisten your seed-starter mix by adding water and mixing it in your larger bin. Continue to add water to the seedling mix until you achieve the moistness of a rung-out sponge. Once you have added the water you can then put your seed starting soil into your containers.

This recipe is the one I like best, but your “taste” may differ a bit. Feel free to experiment with more or less of each ingredient to see how your mix works with your seed starting process.

If you have leftover seed starting mix let it dry well and then you can store it for up to 3 years in a dry bin, bag, or container. After 3 or 4 years the peat moss will start to break down and that will affect the texture of your mix, so use it up before that happens.

Using Seed Starting Mix

Seed starting mix is perfect for starting seedlings in any smaller-sized container. Add the pre-moistened mix to the container, add your seeds, and then cover them with a small layer of seed starting mix or vermiculite.

Keep the soil moist and your seedlings should emerge in just a few days! Seed Starting mix can also be used as a great medium for growing microgreens!

To learn more about the entire seed starting process, consider buying my Seed Starting Simplified course. It is available year-round. Click this link to learn more. Click this link to learn more.

Common Questions about Seed Starting Mix

Will Making my own seedling mix save me money?

Yes! Buying and storing the ingredients may cost more upfront, but the cost of homemade seed starting mix will be 4 to 6 times less per quart of the mix as compared to commercially available seedling mixes.

Where to buy seed starting mix?

Commercially made seed starting mixes can be found at all good nurseries and will also be carried in the garden centers of most big box stores. If you choose to buy instead of making your own, look for an organically certified mix that contains peat moss, perlite, and vermiculite.

Can you reuse seed starting mix?

Yes, if you find you have extra mix, or you decide to remove the plants you are growing it is fine to reuse your seed starting mix as long as there were no disease problems with