Seed Starting Mix: What is it and how to make it?

If you’re new to gardening, or an experienced gardener that isn’t buying started plants and plans to start your own seeds, you might be wondering what the difference between seed starting mix and potting soil is. Why does your seed starting medium matter? Can you use them interchangeably? How about soil from my backyard, will that work?

Seed starting mix and potting soil are two different types of mediums and serve different purposes. Before taking the plunge and investing your time and hard earned money into starting seeds you’ll want to know the differences between the two and how to correctly use them.

Here are the basic differences between the two mediums:

  • Seed Starting Mix: helps seeds germinate into seedlings. It is light weight, fine, loose, and low in nutrients. It helps to maintain moisture and promotes seeds to germinate. Typically composed of peat moss and/or coco coir, perlite, and vermiculite
  • Potting Soil or Potting up mix: Used to transplant up seedlings, or grow plants in containers. It is coarser, denser, and higher in nutrients than seed starting mix. This mix promotes growth and can support rapidly growing seedlings and mature plants. Typically composed of compost, soil, sand, moisture retention granules, perlite, peat moss and/or coco coir, vermiculite

The difference between the two mediums begins with their ingredients. Seed starting mix is typically shorter on the ingredient list and is a soil-less medium; it has a fine, light, and fluffy texture. The primary purpose of seed starting mix is just that – starting seeds! This medium allows seeds to easily germinate and get off to a great and healthy start. Seed starting mix lacks nutrients, which is great for tender young seedlings, but not good for growing plants that need a wide variety of nutrients to support growth. On the moisture front, seed starting mix will hold onto water, without becoming too soggy, which can cause seedlings to rot if they stay too wet for too long.

Potting mix typically has a longer ingredient mix, it’s coaser, denser, and is the perfect medium for transplanting your young seedlings or growing mature plants in pots.

Do you really need seed starting mix to start and grow your own plants?

Technically, no you don’t, however it’s highly recommended. If you are going to go through the hard work and spend time and money on starting seeds, why not get them off to the best possible start! Your seed starting mix will give your seeds the best chance at germinating, it’ll reduce the likelihood of seedlings succumbing to dampening off (this is caused by a fungus) and it doesn’t contain fertilizers. For germinating seeds, fertilizer is not needed and can actually be detrimental. During those first few weeks of life your seedlings will get all of the nutrients that it needs from the seed. Those tender young seedling can actually be injured and burned if there is too much fertilizer in the growing medium. While your seeds will likely germinate in potting mixes and potting soils it can result in longer germination times, the denser and coarser mixture makes it harder for your seedlings to germinate and break through the soil.

You might also be wondering, can you just use soil from you backyard to start seeds – once again, technically yes, but it’s not recommended. Your soil from the backyard really won’t do the job. It will likely be too compacted and heavy, chances are it’s full of weed seeds, and can contain fungi, pests, and pathogens that can result in diseases that could harm or kill your young seedlings.

Both seed starting mixes and potting mixes can be purchased in pre-mixed bags – Farm and garden centers, big box stores, and online retailers like Amazon will all carry bagged mixes. However, you can also make your own mixes – this will allow you to control the ingredients, and if it’s important to you, keep your gardening completely organic. Another benefit of making your own mixes, you can save money! Who doesn’t like saving their hard-earned money? I know I do!

Basic Recipe for Seed Starting Mix:


  • 2 parts coco coir or peat moss
  • 1 part vermiculite
  • 1 part perlite

A part is just an equal measurement – as long as your consistent, you can use anything you have on hand, a cup, a scoop, a bucket, or even whole bags. Mist your ingredients with water, and thoroughly mix all of your components in a large container – a bucket, or wheelbarrow will work well, depending on how much you are making at a time. You’ll want to add enough water to saturate your mixture, but not make it soggy. Giving your seed starting mix a healthy dose of water will help keep the mixture uniformly moist through out the seed starting period.

If you have any left over seed starting mix, you can save it for the next growing season, or use it as the base for making a your very own potting mix.

Coco coir comes in compressed dehydrated blocks and is a byproduct from the coconut processing industry. If you are foregoing peat moss, you’ll need to soak the coir in water before using it. In recent years the use of peat moss (which is partially decomposed spagnum moss harvested from bogs) has become a controversial topic. Almost all peat moss sold in the United States comes from Canada. Peat grows at a very slow rate, just 1/16th of an inch in a year – while it’s technically a renewable resource, it takes hundreds of years to form.

1 thought on “Seed Starting Mix: What is it and how to make it?

Comments are closed.