Best Soil For Seedlings

A Comparison Test – Part 1

Ever wonder if starting seedlings really required special soil? Does a specialized type of growing medium really benefit seed starting? Is there truly a best soil for seedlings? If so, is the benefit noticeable? Is it worth spending extra for? Or, is just plain old dirt fine?

[code_snippet id=5 format]

Seedling Soil Shootout Purpose Outline

This article will be to document a not-scientific-but-somewhat-controlled experiment I performed in the Summer months of 2023.

For this test of best soil for seedlings, I purchased 5 widely available, easily purchased soils/mediums. Some are available at nationwide home improvement garden centers, all are available at Amazon.

I ensured all soil starter cups were evenly filled across soil/medium brands, by weight.

And I wanted to go with relatively quick-germinating seed varieties. There’s a mix of annuals and perennials.

“Plain old soil” is a very subjective term. The native soil available to me on my property is probably very different from yours.

Brands of Soil Tested

All of these seedling-centered soils are readily available and affordable (some are more affordable than others.) My “Best Soil for Seedlings” test starred these contestants:

At $4.99/8 quarts, Miracle Gro Seedling Starter is the least expensive of all tested media.

At $14.35 / 8 quarts, Espoma Organic Seed Starter is the most expensive.

** I’ve purchased these at large home improvement stores also

Seeds Germinated

For this best soil for seedlings test, I wanted to use familiar seeds, ones that I’ve had a history with, and that germinate somewhat quickly. I wanted to test these soils using seeds that are notoriously easy starters (at least in my experience) and I also wanted to use a few seeds that I harvested last year that have already proven to me to be easy to grow (Swamp Milkweed, Snapdragons.)

The seeds purchased through Botanical Interests were very affordable. They ranged from $0.69 to $2.09, during a store-wide 30% off Memorial Day sale. This is my first experience with Botanical Interests. More observations regarding quality to follow. Initially, I’m impressed with BI, I write briefly about my first shipment.

Cosmos “Sea Shells Blend” by Botanical Interests

Gaillardia “Goblin” by Botanical Interests**

True Hyssop Seeds by Botanical Interests

Self-harvested Swamp Milkweed seeds

Hello Yellow Milkweed “Butterfly Flower” by Botanical Interests

Self-harvested Snapdragon seeds *

---

*Image by Gardening Knowhow

**Image by Botanical Interests

All other images by author

Growing Equipment Used

Seedling Cups – Planting Containers

For my best soil for seedlings competition, I decided to use seed cups of the same size. I chose “Ehwine” biodegradable fiber cups, 3″ diameter, available from Amazon. Cost: $14.99, Pack of 100. This product also includes 100 white plastic plant label tags.

Seedling Organization

For ease of moving, I used glass or metal lasagna pans to set the cups into. For the first 4 days, the seedling cups/trays were located on the top-most shelf of my mini-greenhouses. I noted that the close proximity of my home’s siding might artificially raise the local temperature too high, and not beneficial to the seedlings’ best growth. For the remainder of the test, all 5 trays/cups were placed on one table where they received at least 6 hours of direct sun exposure.

Experiment Physical Environment

The first week, I placed the trays holding the seedling cups on the top shelf of my two mini greenhouses. When we experienced hot (for us) days, I thought the temperature in the greenhouses would become too great. I then moved all the trays onto a raised table outside. They all received the same amount of direct sunlight per day. Between 11am and 6pm the area receives direct sunlight this time of the year.

Incidentally, I used a few older baking pans to hold my seedling cups earlier in the year. I bought more at local thrift stores. Buy the kind of pans/trays that have some sort of rim that can hold water. It’s a good practice when beginning seeds to water from below: add water to the tray, not on top of the new seeds as they could get disturbed.

Soil, Sowing Procedure Followed

• I deposited equal amounts of soil to the soil cups by weight, either premoistened or soil with water added afterwards.

• I sowed the seeds as per manufacturer’s suggested method.

• Using mist setting on residential garden hose, I watered all cups at the same time, when needed to maintain a moist soil.

• I recorded the general weather conditions in AM and PM blocks every day (for example, AM: Sunny, warm, or PM: Cloudy, Cool)

• Each soil sample received two samples of all seeds. 6 seed types, 5 soil types, 2 cups each, for a total of 60 seedling cups.

Notable Milestones

There were some milestones of growth that I wanted to record. When these events happened, I made note:

• First seed to sprout, from which soil
• First sprout compared to growth progress in other same seed soil cups
• Relative progress among soils-seedling pairs to determine if there’s a clear ‘winner’

Info Recorded

Recorded Weather During Test

First Soil / Seed Combination to Visibly Germinate & Break Surface

Images above can be clicked for larger view

Day 4

June 7th, in the afternoon, I checked the specimens. I saw that Botanical Interstests’ Cosmos (C. bipinnatus) seedlings had sprouted on Day 4. (The manufacturer states that these Cosmos take 7 days to germinate, so that I got these seeds germinated in 4 days … well… I am a considerate, careful gardener.)

They didn’t sprout in all the soils, though. They sprouted in:

Soil C: Espoma Seed Starter

Soil D: Miracle Gro Seed Starting Potting Mix, and

Soil E: Miracle Gro Moisture Control Potting Soil

Espoma is a new brand to me, and it was a soil that readily absorbed water. The Seed Starting Potting Mix did not readily absorb water, and I think that pre-moistening this soil is a better method. Miracle Gro Moisture Control soil also absorbed water readily.

(I had my money on the Coir, thinking it was the purest medium. Since the coir requires rehydration, it is necessarily pre-moistened, and it was very easy to work with.)

Day 5

June 8th, I noted that another Cosmos seedling sprout emerged in Soil A, Black Gold Seedling Soil.

Day 7

June 10th: Seeds 1 (True Hyssop) started sprouting in soil cups A (Black Gold), B, and E (Miracle Gro Moisture Control). No pictures taken of this occurrence today.

Day 10

June 13th: A few new seed sprouted visibly! Noted that Seed 5, Botanical Interests Galliarda was visibly sprouting in Soil C, Espoma Organic Seed Starter soil.

Somewhat quiet, the “Organic” Coconut Coir and Miracle Gro Seedling Seedling Starter have both sprouted a True Hyssop seed.

If you’re keeping score like I am, Soil E, Miracle Gro Moisture Control Soil, seems to have helped sprout the most kinds of seeds up to this point. Cosmos, Gaillardias, and True Hyssop seeds have sprouted.

Day 17

June 20th

Our weather conditions the past 5 days have been rather un-summer like. It’s been cloudy and drizzly for the most part, with occasional brief sunbreaks.

I took a snapshot of all 5 soil samples, you can click/tap each image for a larger size:

I noted that Soil A, Sungro Black Gold Seedling Mix, had seedling starts in all but one type of seed. It and Miracle Gro Seed Starter is so far the only soil to show Seed 2, Yellow Milkweed, sprouting. Miracle Gro Seedling Starter is the only soil to have Seed 4, my Swamp Milkweed, sprout so far.

I assigned scores. If both seed types were sprouting in a soil sample, they get a 2. If a seed type was sprouting in only one of the brand’s soil sample cups, they get a 1. 0 points for no seed germinated.

The chart is showing that Sungro Black Gold Seedling Mix and Miracle Gro Seed Starting Potting Mix are tied with 9 out of a possible 12. Soil C, the coconut coir, might not be suited for starting seedlings.

It’s not my intention to crown a winner yet, based on these findings. We’re only 17 days into the competition. But, if your objective is getting seeds started as quickly as possible, the Miracle Gro Seedling Starter Mix and Sungro Black Gold Seedling Mix are the better performers in my unofficial test.

Read Part 2 of this seedling soil test. We’ll watch the seedlings grow and see if there’s a noticeable difference between the seedling soils.