Best Seedling Soil to Use For Growing Seeds

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best seedling soil test results

This is a follow-up to Part One of my Best Seedling Soil comparison.

I’ve decided to end this Soil Shootout as of the end of July 2023. This has been a great learning experience, and I’ve had a lot of joy watching seeds come to life! There definitely is a best seedling soil, or, should I say, two excellent choices and a few not-so-great choices.

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Best Seedling Soil Final Progress Report

To recap, I planted 6 different seeds in 5 different soils. Four of the soils are purportedly formulated specifically for growing seedlings. Coconut coir and Miracle-Gro Moisture Control mediums state no such benefit.

Soils Tested

The soils I tested were:

A. Sungro Black Gold Seedling Mix

B. Vivlly “Organic” Coconut Coir

C. Espoma Organic Seed Starter

D. Miracle Gro Seed Starting Potting Mix

E. Miracle Gro Moisture Control Potting Mix

Seeds Planted

And the seeds I sowed to test these soils were:

1- True Hyssop (Botanical Interests)

2- Milkweed “Hello Yello” (Botanical Interests)

3- Snap Dragon (my 2022 harvested seed)

4- Swamp Milkweed (my 2022 harvested seed)

5- Gaillardia “Goblin” (Botanical Interests)

6- Cosmos “Sea Shells Blend” (Botanical Interests)

Executive Summary

Based on my test:

Both Miracle-Gro products, Seed Starting Potting MIx and Moisture Control Potting Soil, hands down out-performed the other 3 soils tested. Sungro Black Gold Seedling Mix and Espoma Organic Seedling Potting Soil cost more than twice as much as Miracle-Gro, and provided much worse results. And, using straight coconut coir for seedlings is not recommended.

The Cosmos sprouted quite well in 4 of the 5 soil samples, and I’ve since relocated the seedlings to their ‘permanent’ garden bed. Now that they’ve got room to grow, I expect the Cosmos to take off.

cosmos seeds growing soil seedling test
Almost all Cosmos seeds sprouted and are growing well! Image by author

I’m quite pleased to have seen 5 of 6 seeds germinate. Those were the Cosmos, the Gaillardia, the Yellow Milkweed, my Snap Dragon harvested seeds, and the True Hyssop. The Cosmos and Snap Dragons are annuals; the other three are perennials and I’ll have them around for years to come (knock on wood.) This means that I’ll have seeds to harvest and grow next year.

Gaillardias are really wonderful flowers to have, if you’re a neglectful gardener. They tolerate heat and drought. The blanket flowers I have in my front yard under the tree receive little attention or watering from me during the summer, yet they are bright and beautiful nonetheless.

Yellow Milkweeds are tall, stately flowers that attract all the pollinators, hummingbirds, and butterflies. Monarch butterflies rely on milkweeds exclusively for food and larval growth. They’re terribly easy to grow and reach 3-4 feet in height.

Cosmos are gorgeous annual plants. To have the Cosmos sprouting within 4 days was sheer joy. Cosmos are a very hardy and lovely annual to have in the garden. Their foliage reminds me of underwater plants, and when they sway in the wind it’s a lovely summertime image. The Cosmos seeds germinated in every medium, even the least impressive, coconut coir.

True Hyssops are new to me, though I’ve had an Anise Hyssop in my garden for the past 3 years and didn’t know it. Their leaves are aromatic and are late summer bloomers. These perennials flourish in nearly all USDA zones (3-11) and will flower their first year.

What is Stratification?

Having had great success with my Swamp Milkweed seeds earlier in the year, I expected them to come raring out of the gates in this soil test. Wah wah – Didn’t happen. Now that I’m a little more experienced gardener, and am learning something new every day, I know what the problem is.

Wildflowers and perennials notoriously require their seeds to experience a period of stratification. Stratification is when the seed is subjected to cold temperatures before sowing, usually for 30 days or more. There’s a mechanical process the seeds undergo that only cold weather can prepare them for. I’ve read in numerous sources that refrigerating your wildflower and perennial seeds for 30 days or more before planting them in the spring after last threat of frost will set your seeds up for successful germination and sprouting.

Seed Quality

I can wholeheartedly recommend Botanical Interest seeds. My experience with them, so far, is that they’re good quality, viable seeds. They’ve shown that they can germinate and sprout. Some seed vendors charge much more. Botanical Interest’s seed offerings are wide, and very affordable.

Now, with all due respect to reputable seed vendors… there’s nothing like harvesting seeds from plants and flowers that have grown in your own garden. The seeds you harvest from your own plants are free, and they’ve already proven themselves to be viable.

Best Seedling Soil Observations & Findings

Miracle-Gro Moisture Control Potting Mix is a terrific medium to use for starting seeds. I wouldn’t have thought, as I added this soil to the testing line-up on a whim. It’s one of the least expensive, widely available soils you can get.

cosmos seedlings grown in different soils to test for best start soil

This image shows Cosmos seed starts, Day 50. E is the pair raised in Miracle-Gro Moisture Control Potting Mix, A is the pair raised in Black Gold Seedling Mix, D is the pair of Cosmos raised in Miracle-Gro Seed Starting Potting Mix, and C is the pair started using Espoma Organic Seed Starter Mix. (Note that Soil B, the Coconut Coir, produced zero viable seedlings, it is not a medium to use for seedlings on its own.)

Miracle-Gro Moisture Control Potting Mix (Soil E)

best seedling soil comparison test winner
best seedling soil comparison test winner miracle gro moisture control potting mix

Cost
One of the less expensive soils I tested. About $5 for 8 quarts, which is about 3 pounds. This size bag will fill two 8″ diameter potting containers.


Absorbency
Quite absorbent. Absorbs water well when initially seeding. You do not have to premoisten this soil. You can add the soil to your seedling containers and water them after. Very convenient.

Organic nature
Doesn’t claim to be organic.

Ingredients, additives
Well balanced combination of soil, vermiculite.

Overall impression of gardener
Adding this soil to this test was on a whim. It isn’t advertised or promoted as being made specifically for starting seedlings. In my experience, you can’t go wrong using this soil when you start seeds.

With one exception, all seeds germinated, sprouted, grew, and thrived in this soil. All of the sprouted seeds have matured enough to have been planted in their permanent spot in my gardens.


Claims to provide automatic moisture control. It protects against over- and under-watering. This is a pretty impressive feature.


In my test, seeds germinated the quickest and grew strongest using this soil.

harvested snap dragons and hyssop seeds grown in miracle-gro moisture control soil
Day 50 of test: Miracle-Gro Moisture Control raised Hyssop and Snap Dragon seedlings
Day 50 of test: Miracle-Gro Moisture Control soil-raised Gaillardias, planted in their forever bed
Day 50: Comparison image showing Cosmos seedlings (planted in their “forever” bed) started in Miracle-Gro Moisture Control (E), Black Gold Seed Starter (A), and Miracle-Gro Seed Starter Mix (D).
snap dragon seedlings planted in regular bed

Even my harvested Snap Dragon seeds are thriving in Miracle-Gro Moisture Control mix.

Miracle-Gro Seed Starting Potting Mix (Soil D)

best seedling soil comparison test winner
best seedling soil potting soil miracle gro seed starting potting mix

Cost
Both Miracle Gro soil mixes were the least expensive, at about $5 for 8 quarts.

Absorbency
You will need to premoisten this soil before adding to seedling cups and seeding. Merely filling the seed cups with this soil, it will literally reject water.


Organic nature
No claim of being organic.


Ingredients, additives
Some perlite, but there’s also a surprisingly high amount of little twigs and large matter pieces. Some gardeners might feel the need to sift these chunks out. That’s adding another step that I think isn’t warranted.
Both the Miracle Gro products have large organic chunks and pieces of what is decidedly not soil, peat moss, perlite or vermiculite. Bits of twigs, perhaps? Pieces of tree bark? However, the final results indicate that these larger chunks don’t detract from their excellent germination qualities.


Overall impression of gardener
I’ve used this soil mix quite a bit this year, and have been very satisfied with my results, for the most part.
The requirement to premoisten the soil is a little bit of a hassle. Imagine filling some seed cups up with this soil, and watching whatever water you carefully pour go sliding off the top like it was sealed with plastic wrap! Because of this characteristic of the soil, I’m relegating Miracle-Gro Seed Starter Mix to Second Place. Beyond that, I was happy with the results achieved. I will continue to use this soil when I start seeds.

milkweed seedling starts doing well in miracle-gro soil

Miracle-Gro Seed Starter showing seed starts of Hello Yellow Milkweed (Left) and True Hyssop (Right.)

cosmos flower starts from seed in seedling starter soil

Cosmos starts. Left two are from Miracle-Gro Seed Start soil. Since this picture, they’ve grown to about 12″ high.

true hyssop seedlings from miracle-gro seed starter mix

True Hyssop seedlings (raised in Miracle-Gro Seed Starter mix) planted in their forever home.

Sungro Black Gold Seedling Mix (Soil A)

sungro black gold seedling mix comparison test

Cost
This was one of the pricier soils I tested, $14.10 for an 8 quart bag. That’s nearly three times the price as either Miracle Gro soil.


Absorbency
Another soil that doesn’t need to be premoistened to work with. Simply fill your seedling containers, add seed, and water. Convenient.


Contents of medium
Contains a fair mix of vermiculite, an additive that helps give the soil a little expansion, not so dense, which is helpful for seedlings’ young tiny roots.


Along with Espoma, these two soils contain the widest mixture of additives. It’s a light-weight medium.


Organic nature
Is certified organic from OMRI.
Is a product of Canada.


Ingredients, additives
Claims to be made for seed germination, use with cuttings, cell packs and seedling trays or flats.


Overall impression of gardener
This was a very nice product to work with. I’ve used Black Gold products in the past and have a positive view of them.
This soil was the only one that promoted germination and sprouting of all except one seed – my (tough?) Swamp Milkweed seed I harvested from a mature plant last fall. Only Miracle Gro Seed Starter was able to germinate that seed.
This soil, along with Miracle Gro Seed Starter, is the only soil to have germinated Seed 2, the Yellow Milkweed seed from Botanical Interests.


But is Black Gold worth paying three times as much as Miracle-Gro?

Vivlly “Organic” Coconut Coir (Soil B)

best seedling soil coconut coir brick test comparison

Cost
It’s sold in a 1.4 pound ‘brick’ that cost me $8.79. More than the two Miracle Gro products but considerably less than the higher priced soils I tested.


Absorbency
This product simply requires you to premoisten before using. Instructions are to separate the brick into small pieces and then add a gallon of water. This water will rehydrate the coir, making it swell. You cannot avoid this step.


I think that the very nature of coconut coir made it retain moisture the best, even compared to Miracle Gro’s Moisture Control. During daily watering of the test subjects, I frequently noted that the coir stayed moist, and needed less watering.


Contents of medium
100% coconut coir.


Organic nature
While this claims to be “organic” there isn’t any certification to back it up.


Overall impression of gardener
First off, this is a lovely, wonderful medium with which to work. It really is fun to break the brick apart in a large bucket, add water, and watch it swell.


You need to incorporate the water into the coir which requires some handiwork. A little extra effort, yes, but you really get to know your medium when you do this!


Sadly, this all-coconut-coir, on its own, showed unimpressive results with my seeds. I think it’s a wonderful medium to use on established plants, perhaps as a 50-50 mix with ‘regular’ soil. I think the problem is that coir doesn’t allow much air circulation. I think that adding vermiculite or perlite to coir would make coir a more viable potting soil or addendum to potting soil.


I love that it’s reusing something that might otherwise just be seen as unusable waste. I will probably buy more coir, but not for seed starting.

coconut coir is not recommended to use as a seedling start medium

Coconut coir is the reddish colored soil in all but the bottom right two cups. The majority of the light green material you see is added solid fertilizer. The quality of the few seedlings that did sprout are negligible. Coconut coir is definitely not one of the best seedling soils you can use.

Espoma Organic Seed Starter Mix (Soil C)

espoma organic seed starter potting mix comparison test

Cost
The most expensive soil tested, $14.35 for 8 quarts.


Absorbency
This soil requires you to premoisten before adding to seedling cups. If you just add soil to cups, then add the seed, the soil will not absorb or accept the water. It will pool on top, requiring some hand manipulation.
Plan on using a large bucket: deposit the whole bag of soil, then start by adding 1/2 gallon of water to moisten the soil. When the soil feels moist, you may then add to your seedling containers.


Contents of medium
A good mix of soil to vermiculite. Provides a little breathing room for seedlings’ tiny roots.
Contains “Myco-tone”
Helps to “balance moisture retention.”
“This product is formulated from 80-90% sphagnum peat moss, perlite, limestone to adjust pH, and yucca extract.” It’s a very lightweight medium.


Organic nature
Claims to be organic. Organic lettering is the largest lettering on the bag!

Overall impression of gardener
For what I paid for it, I shan’t recommend it. It’s germination was ‘meh’ at best.
This soil was able to germinate the Cosmos seeds by the 4th day. Impressive, surely. But then things just … petered out after that.
Hyssop seeds germinated but you had to get a magnifier out to see. As of Day 14, no other seeds germinated besides these two. By the end of the test, Day 50, these seedlings had wilted away.


The coconut coir germinated and sprouted seeds slightly better than Espoma, and all soils were less expensive and returned much better sprouting results. In the end, Espoma returned only two viable seedlings able to be planted in a permanent garden bed. Both are Cosmos.

Pre-moistening requirement, expensive, and less than stellar results sprouting seedlings relegate this soil to dead last in my test.

What To Do Next?

That wraps up this soil seedling test to find the best medium. These 5 soils clearly aren’t all the choices available to you, but they do represent the most readily available brands. If you’ve not used Miracle Gro’s Moisture Control or Seed Starter Mix, I’d urge you to try them next time.

If you have a favorite seedling starter soil you use, let us know in the comments below! Thanks for reading!

seed starter seedling test graphic
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Author

After years of denying it, Donald finally admits one passion in life is gardening. More specifically: growing seeds, plants, flowers and edibles and helping them to be the best possible. Neighbors call him a Green Thumb. He lives in Western Washington with his wife of 24+ years and three cats.

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