Seed Starting Mix vs Potting Soil: What's the Difference? - Backyard Boss
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Seed Starting Mix vs Potting Soil: What’s the Difference?

Imagine you’re at a garden center trying to decide which type of soil you need to start a garden while staring at dozens of different bags of soil. When it comes to soils, one size doesn’t fit all! While some soils are great for flowers, others are suitable for succulents and cacti.

Even when you are an experienced gardener, it’s sometimes challenging to pick the right soil, not to mention if that’s your first time figuring out what potting media is best for your garden. That’s why it’s good to realize first that seed starting mix and potting soil are two sides of the same coin. Then, you can get deeper into the subtle differences between them to know how they can affect your plants’ growth. 

Defining Seed Starting Mix and Potting Soil

different soils
Image credits: Anna Shvets via Pexels

To understand which growing media you need to use for your garden, you’ll need to understand the basic differences between the two to make the right choice for your plants.

What is a Seed Starting Mix?

A seed starting mix is a lightweight and airy soil with higher percentages of perlite and vermiculite, both of which are inorganic materials. Perlite is a hard and highly porous material created by intensely heating volcanic glass, whereas vermiculite is a soft, porous substance made from extremely hot mica.

Vermiculite is also rich in potassium, magnesium, and a little calcium, which it slowly releases in the seed-starting mix. Since the mixture is lightweight and airy, seeds can easily form roots after germinating.

What is Potting Soil?

Compost, peat moss, vermiculite, and perlite are some of the main components of potting soil. Although potting soil sounds a lot like potting mix, they are two different soils that you shouldn’t use interchangeably. In addition, potting soil has a coarser texture and is heavier than potting mix or seed-starting mix.

Potting soils can be fully organic and may or may not contain garden soil. However, this varies from brand to brand, and you’ll need to read the label carefully before using it. This is because if it contains soil, the soil may contain some weed seeds.

You may want to sterilize your soil, but know that some aggressive seeds will still survive the heat.

In A Nutshell

Seed-Starting Mix Potting Soil
Lightweight and Airy Dense and Nutritious
Contains perlite and vermiculite Contains compost, peat moss, perlite, vermiculite, and possibly soil
Sterile May contain weed seeds
No organic matter Contains organic matter
Can’t be refreshed Can be refreshed

Difference Between Seed Starting Mix and Potting Soil

Bag with Soil on Wooden Table
Image credits: pixelshot via Canva

It’s wise to know the importance of being able to DIY your potting soil, whether to save a little money or have complete control over the environment your plants grow in. Knowing how to make your organic potting soil or seed starting mix is valuable information that will provide you with long-term benefits.

Whether you want to save some money or have complete control over your plant’s environment, DIYing your potting soil is an optional way forward.

1. Composition

Soilless seed starting mixtures have a smoother texture and contain peat moss, sphagnum peat moss, perlite, coir, and vermiculite. Potting soils typically have a rougher texture and may contain coconut coir, vermiculite, peat moss, perlite, soil, compost, and sometimes, manure. Some potting and seed-starting mixtures may also include fertilizer as an ingredient.

Coconut coir is a coarse, short fiber from the coconut’s outer shell. It is the thickest and most resilient of all commercial natural fibers. You can use this as an alternative to peat moss because it is easier to rehydrate.

Some brands add moisture retention granules with peat moss, which expand 400 times their size as they absorb water. These are useful for container gardening during dry weather and drought.

2. Uses

The three primary purposes of growing media are to:

  1. Physically support the plant,
  2. Promote maximal root growth, and
  3. Supply roots with nutrients, air, and water.

Use seed starting mix for germinating seeds and helping them grow healthy roots while providing them with nutrients, air, and water through the porous nature of its finer granules. Due to newly germinated seedlings’ vulnerability to damping-off fungal diseases, the fine sphagnum peat moss and perlite will help lighten the mix and allow it to drain more quickly.

Potting soil is more “all-purpose” that’s formulated to produce uniform plant growth.

In A Nutshell

Seed-Starting Mix Potting Soil
Finer textures Coarser textures
Contains peat moss, perlite, coconut coir fiber, vermiculite Vermiculite, compost, peat moss, perlite, composted manure, and maybe the soil
A few brands may contain fertilizer May have fertilizer
May contain sphagnum peat moss Only some brands contain sphagnum peat moss
May contain moisture-retention granules May contain moisture-retention granules
Could contain coir Could contain coir
Focuses only on seeds All-purpose and uniform plant growth

Where to Use Potting Soil and Where to Use Seed Starting Mix?

pots and seedling
Image credits: Ylanite via Pixabay

While most gardeners prefer to use a seed starting mix for planting seeds and potting soil for transplanting them, you can decide which one to use for your garden depending on the climatic conditions and availability of the soil, of course.

Generally, seed-starting mixes help sow small seeds and germinate seedlings. However, ensure that your seed-starting mix doesn’t contain any fertilizer. Once the seeds have germinated, you can add a diluted fertilizer solution to help them grow after transplant.

On the other hand, if you live in a dry climate that experiences frequent drought, you can use potting soil for your seeds and plants. Read the label to know if the potting soil contains moisture-retaining polymer gels, which lower the need for frequent watering during the growing season.

Although you can use seed-starting mixes for specialty gardening, you can also use potting soils, provided you follow recipes and mix the right ingredients and proportions to make an ideal growing medium for your plants. For example, your can use potting soils to grow succulentscacti, flowers, herbs, fruits, veggies, and container gardening.

Oh, Grow Up Already!

Good potting mediums are the reason behind a healthy, thriving garden. Generally, seed-starting mixes add incredible benefits to seeds and seedlings, while potting soils provide broad support to plants.

Although there are wide varieties of seed-starting mixes and potting soils online and offline, you can easily modify your blends to suit your seed or plant’s needs and store them for future use.

Leave your experiences, thoughts, and questions in the comment section, and as always, please share!

Happy Gardening!