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How to Make a DIY Seed Starting Mix

Whether you’re a new or experienced gardener, starting seeds can be expensive. Between purchasing a variety of seeds and updating your equipment, you may have already reached your max budget.

Why not save some money by creating your own DIY seed starting mix? It’s a great way to start seeds on a budget, and you can customize the ingredients to your liking.

In this post, I’ll go over the essential ingredients of seed starting mix along with how to make it. Keep reading to try out a DIY seed starting mix project yourself!

Closeup of celery seedlings in seed starting mix.

Benefits of Creating DIY Seed Starting Mix

Save Money

This is always my favorite perk of any DIY project – save money! You may spend a little more upfront for ingredients. But, in the end, you’ll have a ton of DIY seed starting mix to last you all season.

A typical bag of seed starting mix runs around $12 to $15 for an eight-quart bag.

Purchasing the essential ingredients of a DIY seed starting mix will cost around $45. But you’ll be able to create five times the amount of seed starting mix (if not more).

There’ll be no need to run to the store for another bag of seed starting mix. All you’ll have to do is re-wet your mix or create more from your ingredients.

Control of Ingredients

If you’re an organic gardener, you may prefer more control over what goes into your garden. Or, maybe you’re just tired of purchasing seed-starting mixes that don’t perform well.

By making your own mix, you’ll be in charge of what ingredients make the cut. Or, you can add an ingredient you think your seeds are missing.

Woman making DIY seed starting mix or potting soil.

That also means you won’t have to rely blindly on a store-bought mix being organic.

I’ll go over which ingredients work for organic mixes further down in this post.

Better Drainage

Along with control of ingredients, you can manipulate the texture of your mix.

Read the review of any pre-mixed seed starters, and you’ll see complaints of unsifted materials. This could be large chunks of compost or bark.

This directly affects seedling drainage, and it could create air pockets around the roots. Consequentially, seedlings could lack the hydration and nutrients they need.

You can make sure that only the finest materials make the cut by sifting through your own ingredients.

What Should Be in DIY Seed Starting Mix

First, let’s go over the three essentials that should be in your DIY seed starting mix.

Peat Moss

Peat moss, a component in DIY seed starting mix.

Peat moss is the main component you’ll see in most seed-starting mixes.

It may have the appearance of soil, but feel it, and you’ll know the difference. Peat moss is dark brown like soil, but the texture is fibrous and spongey.

Where does it come from? Over thousands of years, sphagnum moss and other mosses decompose in peat bogs in Canada. The end result is a natural material known as peat moss.

Because it’s so lightweight and fibrous, peat moss is great for adding aeration and drainage to your DIY seed starting mix. The texture is also ideal for young seedlings to establish roots in.

You can purchase a sizable bag of peat moss for around $15.

Note – some organic gardeners prefer not to use peat moss because of the carbon dioxide released when it’s harvested. A good organic alternative to peat moss is coconut coir.


Perlite, another component in DIY seed starting mix.

Perlite is the next ingredient that you should implement into your mix. You may be more familiar with it than you think. If you’ve ever noticed the small white beads in seed starting mix, you’ve seen perlite.

Perlite is a natural additive that is great for improving drainage. The small white beads break up the growing medium and allow air to flow around the roots.

Technically, perlite is a mineral that comes from volcanic glass. The mineral is created when molten lava cools and traps water inside. Upon being heated, the mineral expands into the lightweight perlite we see.

Perlite is safe to use for organic gardeners, and it’s cost-friendly.


Vermiculite, a final key ingredient in DIY seed starting mix.

While perlite helps with drainage, vermiculite mainly helps with moisture retention.

Vermiculite is also a mineral, but it’s mined from the ground instead.

Vermiculite is porous and able to absorb moisture. The expanded mineral helps the growing mix get the moisture it needs without being weighed down.

That means your seedlings aren’t sitting in soggy soil, but they’re also not drying out quickly.

Just like perlite, vermiculite is created and expanded by heat application. That means the mineral is sterile and non-toxic. There’s nothing to worry about here, organic gardeners!

Optional Ingredients

Now, let’s talk about some optional ingredients you can add to your DIY seed starting mix. These are great for adding a healthy amount of nutrients into the mix.

Young seedlings don’t require nutrients, so that’s why these are optional. You want to be diligent about not adding too much. But, they can help seedling growth as you transition into the garden.


Person holding handfuls of compost.

Using compost is an organic way to add nutrients to your DIY seed starting mix. It can also help improve the texture of your mix if sifted properly.

Compost is normally composed of different decomposed organic matter. This could include manure, decomposed plants and vegetables, and decomposed recycled materials.

Compost is very affordable, so you won’t break the bank with this add-in. It’s usually sold in large bags for $5 to $10.

To purchase compost, check with your local plant nursery or garden center.

Worm Castings

Person holding handful of worm castings.

Worm castings, also known as earthworm manure, are another wonderful add-in if you want your seedlings to receive natural nutrients.

Worm castings help with drainage, and they break up the soil around roots for added airflow. But, their main perk is that they slowly release nutrients to your seedlings without overwhelming them.

Next time you’re digging in your garden and see earthworms, rest assured it’s nothing but good news for your soil!


Greensand is a sandy soil amendment that helps with water retention. It’s a type of sandstone that’s known for its potassium content. It’ll slowly release potassium to seedlings, along with a small amount of iron, magnesium, and lime.

This mineral should be added in a very small amount when creating your DIY seed starting mix. It should only make up approximately 1/20 of your mix. So, it’s best to just sprinkle it in.

Rock Phosphate

You may have guessed its benefit by the name.

Rock phosphate is a good source of phosphorus for young seedlings. Phosphorus is known for helping plants with root formation, which is vital for seedlings.

Its appearance is similar to dust, as the mineral is mined from sedimentary rock.

Just like greensand, it should be added in a very small amount (1 part rock phosphate to 20 parts seed starting mix).

How to Create DIY Seed Starting Mix

1. Gather Supplies

Before you start measuring and mixing, make sure you have all your supplies gathered.

Ingredients for seed starting mix.

Here are a few things you’ll need:

Set all your supplies and ingredients out on a table so they’re handy whenever you need them.

2. Measure and Mix

Now, it’s time to measure out your ingredients and pour them into the bucket.

If you’re using the three essential ingredients for DIY seed starting mix, use this recipe:

  • One to two parts sphagnum peat moss
  • One part perlite
  • One part vermiculite

How much you need will depend on how many seeds you are starting. You can use a measuring cup or any scoop to measure your ingredients. Just make sure to be consistent.

Remember — you can always come back and mix more!

Before you pour your ingredients into the bucket, make sure to sift out any large pieces. You can sift by pouring ingredients through a soil sifter, grate, or chicken wire.

After you’ve sifted, mix all your ingredients by hand until well-combined.

3. Add In Water

Now, it’s time to add water.

You may be tempted to skip this step, but it makes it much easier to add to seed trays. It helps reduce air pockets, and it’ll keep your seed trays from drying out as quickly.

There’s no specific amount of water to add. You simply slowly add water until the consistency is correct.

You want the mix to have the texture of peanut butter. Take a handful and try to stick it to the side of the bucket. It should stick rather than run off or fall apart.

Then, you’re ready to begin filling your seed trays with your very own DIY seed starting mix!

Wrapping Up DIY Seed Starting Mix

By creating a DIY seed starting mix, you’ll be able to save money and control the ingredients and texture. It’s a quick and easy process to master. You may even find yourself learning a lot about what goes into seedling growth.

Rather save time and buy a pre-mixed seed starter? We understand. Check out our recommendations for the Best Seed Starting Mixes for indoor gardeners!

Start this growing season out strong. Learn more about how to grow your favorite vegetables by visiting our Seed Starting page for lots more blog posts and guides.