I used to make my own seed starting mix. No more! Don’t get me wrong. Seed starting soil is very important to the success of your seedlings. It’s important enough that you might want to completely control the process and make your own.
One year I bought a bad batch of mix, and my seedlings turned out awful. In fact, they were so bad that I couldn’t use them and ended up buying seedlings from a nursery.
Still, mix is so inexpensive, easy and fast to buy online, it doesn’t really make sense to mix your own anymore. It’s cheaper and also better to have the professionals make it, rather than buy the ingredients in bulk and do it yourself.
So, to help make sure you don’t get a bad product (as I did), I’ve conducted an unbiased test of the four top seed starting mixes. Here’s what I learned:
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Starting seeds is an exciting time for gardeners. Seeing those first green sprouts emerge from the soil brings hope for the bounty to come. While specialized seed starting mix is ideal potting soil can work in a pinch. However there are some drawbacks to using regular potting soil that you should consider.
What is Potting Soil?
Potting soil is a soilless growing medium made for container gardening. It contains a blend of ingredients like peat moss, perlite, vermiculite, compost, and sometimes fertilizers. This loose, lightweight mix allows for proper aeration and drainage in pots and planters.
Potting soil comes in different formulations tailored to specific uses. Seed starting mix is a type of potting soil designed specifically for starting seeds. It has a finer texture and lower nutrient content compared to general potting soil.
Can You Use Regular Potting Soil to Start Seeds?
Yes, you can use regular potting soil to start your seeds. Seeds contain their own food supply to sustain growth until the seedling emerges and forms its first true leaves. They don’t require extra nutrients at first. So while not ideal, potting soil will work in a pinch.
However, potting soil does have some drawbacks for starting seeds:
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Density – Potting mix tends to be denser than a proper seed starting mix. This can restrict root growth and drainage.
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Nutrient levels – Potting soil usually contains fertilizers. While helpful for mature plants, excess nutrients can actually hinder germination and increase risk of damping off disease.
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Organic matter – Ingredients like compost introduce microorganisms that can cause seedling diseases Seed starting mixes use sterile components,
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Texture – Potting soil has larger particles that don’t provide the fine environment young seedling roots prefer.
So while possible, potting soil is not ideal for starting seeds. You may get lower germination rates, weaker seedlings, and issues like damping off. Specialized seed starting mix gives superior results.
What Makes a Good Seed Starting Mix?
An ideal seed starting mix is lightweight, sterile, and fast-draining. It gives seeds the proper environment to sprout and grow strong until ready to transplant.
Here are the characteristics of a high-quality seed starting medium:
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Lightweight ingredients – Peat moss, perlite, vermiculite, and coconut coir give fluffy texture for easy root growth.
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Good drainage – Excess moisture can lead to fungal diseases. Ingredients like perlite provide drainage.
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Moisture retention – Peat moss and vermiculite hold water so seeds don’t dry out.
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Neutral pH – Most seeds germinate best at a neutral 6.0-7.0 pH range. Lime is often added to adjust pH.
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Sterile – Lack of microorganisms prevents damping off and other diseases.
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Soilless – Contains no actual garden soil which can compact and contain weed seeds.
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Nutrient-free – Avoids excess nutrients that can inhibit germination.
Following a basic seed starting mix recipe using sterile, soilless ingredients will provide ideal conditions for your seeds.
Make Your Own Seed Starting Mix
You can easily make your own seed starting mix at home for a fraction of the cost of buying premixed soil.
Basic Seed Starting Mix Recipe
- 1 part sphagnum peat moss or coconut coir
- 1 part vermiculite
- 1 part perlite
Instructions
- Combine ingredients in a large bucket or tub.
- Add water until moist but not soggy.
- Fill seed starting containers.
- Sow seeds according to package directions.
Customize this basic recipe by adding compost, worm castings, or organic fertilizer for an extra nutrient boost once seedlings emerge.
Tips for Using Potting Soil to Start Seeds
While not ideal, potting soil can be used to start seeds in a pinch with a few adjustments:
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Choose a lightweight potting mix over dense topsoil-based varieties.
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Add extra perlite or vermiculite for better drainage and aeration.
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Use small containers like cells or flats that won’t retain excess moisture.
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Allow the potting mix to fully dry out between waterings to prevent damping off.
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Transplant promptly once seedlings emerge to avoid overexposure to nutrients.
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Bottom water by partially submerging containers to prevent splash-over of wet soil onto stems.
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Disinfect any reused containers to prevent transfer of diseases between generations of plants.
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Sterilize used potting soil before reuse by baking in the oven at 180°F for 30 minutes to kill pathogens.
While potting soil is not the best choice for starting seeds, taking a few extra precautions can help overcome some of the drawbacks and yield successful seedlings.
Frequently Asked Questions About Potting Soil for Seed Starting
Does potting soil go bad?
Potting soils containing organic materials like peat moss and compost will decompose and break down over time. They may begin to grow mold if left wet. For best results, use fresh potting mix within a year or two of purchase.
Can old potting soil be reused?
Used potting soil can be reused if sterilized by baking or steaming to kill any plant pathogens. Refresh with new amendments like compost or coconut coir to replenish organic matter.
Is potting soil better than garden soil for seeds?
Potting mixes are designed to be loose, lightweight, and fast-draining – better suited for starting seeds than heavy garden soil. However, specialized seed starting mix is even better optimized than regular potting soil.
Does seed starting mix expire?
Dry seed starting mix can be used for many years if stored properly away from moisture. Eventually, organic components like peat moss will break down. But sterilized mixes over 2 years old can still be reused with the possible addition of fresh amendments.
Can I use coco coir instead of peat moss?
Yes, coco coir makes an excellent peat-free substitute in seed starting and potting mixes. It offers similar moisture retention and texture as sphagnum peat moss with the added benefit of being a renewable resource.
Conclusion
While potting soil can technically be used to start seeds, a proper seed starting mix will provide better conditions for germination and early seedling growth. The fine texture and sterile, soilless ingredients in commercial seed starting mixes give seeds the best chance at success.
Making your own custom seed starting soil is simple, affordable, and allows you to control the ingredients. With a basic homemade blend, you can give your seeds the ideal nurturing medium to sprout and thrive.
Promix Organic Pro Seed Starting Mix
Manufacturer: Premier Horticulture
Ingredients:
- Canadian sphagnum peat moss
- Coir (coconut fiber)
- Perlite
- Limestone
- Organic Fertilizer
- Mycorrhizae – PTB297 Technology
According to Premier Horticulture, mycorrhizae helps you in two ways. It:
- Prevents diseases (such as dampening off)
- Helps break down the organic fertilizer so the plants can use it sooner
Features & Benefits:
- Stimulate vigorous growth, strengthen roots, improve stress resistance and resist transplant shock
- Manages moisture levels and protects against root rot
- Feeds plants gradually for up to three months
- Certified safe for organic gardening (OMRI-listed)
Important details: This mix was the second best performer. It came very close to the Burpee.
Related: What are the Best Potting Benches for Vegetable Gardeners | If you repot plants often or use a soil block maker, you probably are going to need a potting bench.
The seeds in this soil sprouted immediately after the Burpee mix. Plus, the plants were almost as vigorous as the top performer. There were absolutely no signs of dampening off.
Soil blocks that I made with Promix held together well. I recommend this product if you are going to use a soil block maker.
You can get more details, including pricing, on Promix Mix here. The
Burpee Organic Seed Starting Mix
Manufacturer: Burpee
Ingredients:
- Primarily coir (coconut fiber)
- Organic plant food (No details given)
Features & Benefits:
- Formulated for neutral pH, which is ideal for most plants
- Speeds plant and root growth
- Provides improved root aeration
- Certified safe for organic gardening (OMRI-listed)
Important details: Burpee is the best performer. The seeds in this mix sprouted first and were the most vigorous. Plus, there were absolutely no signs of dampening off.
Surprisingly, this mix has a more orange color when compared to the others. I expect that this is because it’s made primarily of coir. There seems to be no perlite as part of this recipe.
Unfortunately, Burpee Seed Starting Mix did not perform well when I used a soil block maker. The blocks didn’t hold together well. It was so bad that the blocks crumbled whenever I tried to move them.
If you are using a soil block maker, you should use Promix. It worked well with my soil block maker.
You can get more details, including pricing, on Burpee Mix here. The