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Seed Starting Mix vs Potting Soil

Discover the differences between seed starting mix vs potting soil to kickstart your garden's growth. Learn which is right for your seeds and plants!

seed starting mix vs potting soil comparison

It's the start of a new growing season, and you're confronted with a huge aisle of soil bags at the garden center. You're planning to start a few plants from seed and buy transplants for pots. Do you really need both seed starting mix AND potting soil?

Understanding these two products and their unique roles is vital for nurturing healthy, happy plants. Whether you're growing beautiful flowers or delicious vegetables, selecting the right growing medium can make a world of difference.

seed starting mix vs potting soil side by side comparison

In the seed starting mix vs. potting soil debate, it's all about timing. Plant seeds in seed starting mix for easier germination and root development. After your seedlings sprout their first true leaves, switch to potting soil for necessary nutrients.

Let's take a closer look at each type of soil and figure out which one is right for your plants!

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What is seed starting mix?

Seed starting mix is a soilless medium specifically designed to give your seeds the best possible start in life. Unlike typical garden soil, seed starting mix is sterile. It's made up of light, airy components like peat moss, coconut coir, and perlite.

seed starting mix in white bowl

These ingredients serve two main purposes. First, they make it easy for the young seedlings to push through and establish their delicate root systems. Second, they retain moisture, ensuring the seeds stay hydrated but not waterlogged.

However, it's essential to note that while the seed starting mix provides a perfect physical environment for your seeds to sprout, it does not supply any nutrients. The seed itself contains all the nutrients required for the plant to sprout and grow its first leaves.

What is potting soil?

Potting soil, also known as potting mix, is composed of a blend similar to the seed starting mix but includes additional ingredients, such as compost. Well draining potting soil often contains larger materials like bark or wood chips, which help with drainage and aeration.

potting soil in white bowl

So why can't you use potting soil for starting seeds, even if they have similar ingredients? Well, you can, but the larger chunks in potting soil can be too difficult for seedlings to push through, hindering their growth.

Once your seedlings have sprouted and grown their first set of true leaves, they no longer rely solely on the nutrients from the seed. While you can provide your seedlings with liquid fertilizer to fuel their growth, eventually you will need to transition your young plants into potting soil or the garden.

Can you start seeds in potting soil?

Yes, technically, you can start seeds in potting soil. Just keep in mind that you may have lower germination rates because some of the seedlings are trapped under a chunk of bark and can't push to the surface.

One way to fix this issue is by sifting your potting soil before you plant your seeds. This will remove the larger pieces and create a medium that is closer to seed starting mix. A simple mesh screen held over a bucket is all you need!

sifting potting soil to remove larger pieces for starting seeds

If you're starting seeds in soil blocks, potting mix tends to hold its shape better over time. You can just filter out the large chunks or create your own mix using a recipe like the one shown in the video below.

Can you use seed starting mix instead of potting soil?

If you're left with half a bag of seed starting mix at the end of spring and don't want to save it for next year, you can add it to your potting soil to top off a larger container. I would sprinkle in some slow-release fertilizer to adjust the nutrient ratio, just in case.

seed starting mix bag

However, you shouldn't fill an entire pot with just seed starting mix. It won't provide any food for the plant, so you'll end up spending more money on fertilizer than if you just bought potting soil in the first place.

I hope this article helped clear up any confusion about the differences between seed starting mix and potting soil. While the ingredients may look similar, your gardening success depends on choosing the right one for your growing situation.