By seed starting mix I mean any seed starting medium, e.g. rock wool, peat moss, coco coir, etc.
In January, YouTube creator Soil and Margaritas / Garden Life published a video of her latest experiment around potting mixes (that’s right, potting mixes) for starting seeds indoors.
Her rationale for starting her seeds in potting mix is when she uses seed starting mix, she eventually transplants them to potting mix anyway. She acknowledges that not all potting mix is suitable for starting seeds - for example, one of the specific products she tested was very chunky, which significantly hindered those seeds’ germination and growth. That said, she claims that some potting mixes are “fluffy” enough to work well enough for starting seeds.
She tests Chinese noodle beans, sunflowers, and zinnias w/ six products:
- Vermont Compost Company Feed the Soil Fort Vee All Purpose Compost Based Potting Mix (the one she used in 2025)
- Miracle Gro Potting Mix
- Promix Premium Moisture Potting Mix
- Fox Farm Ocean Forest Potting Soil
- Black Gold Natural & Organic Potting Mix Plus Fertilizer
- Espoma Organic Potting Mix
Not accounting for price, personally I’d rank the performance as follows:
- Vermont Compost Company Feed the Soil Fort Vee All Purpose Compost Based Potting Mix (the one she used in 2025)
- Miracle Gro Potting Mix
- Fox Farm Ocean Forest Potting Soil
- Promix Premium Moisture Potting Mix
- Black Gold Natural & Organic Potting Mix Plus Fertilizer
- Espoma Organic Potting Mix (performed the worst, although she acknowledges in her video that this particular product is very chunky and this company has a seed starting mix on the market)
What do people of c/gardening use for starting their seeds? What are your thoughts on this test?
Honestly have only tried seed starter mix but have seen people on YouTube have success with screening potting mixes and using that. Probably just depends on the potting mix composition though.
Sorry you about made me spit out my coffee.
Beans, zinnas and sunflowers are some of the less picky species for substrate. Both sunflowers and beens have large seeds and enough stored energy to supply the plant to the second true leaf. Zinnia’s have extremely durable and high germinating seeds. For testing seedling mixes they are a poor choice. Mainly because they will do well in most things.
There is no “correct” seedling mix for everything. Every species has its own optimal growth medium based upon its unique needs.
What works well for tomatoes is too fine for squash. What works for cantaloupes holds too much water for watermelons. Then there is the whole slow germinating flower seeds. That’s a mess of different preferences.
I see your point. In the case of the YT video I linked in the OP, the tester considered variety of crops as a factor, but perhaps you’re right that those particular crops do not represent a diverse enough set of “pickiness” among seeds. Toward the end of her video, she does acknowledge that what makes sense for her may not make sense for all of her viewers growing different crops in different climates, and she encourages her viewers to run their own tests. Thanks for chiming in on that.
I use starter cubes, or when I use soil (like up potting) I just use my own soil from my garden, and give it a feed if the plants say they need it.
This year I just used the only soil that was available at the store. The grounds still frozen haha, I can use it for other starts if I do them. Just my early starts are done, being peppers and tomatoes.
Do you plan to reorder the starter cubes when you run out? I must say that I’ve really enjoyed your updates - please keep 'em coming!
Yes, they are common stock for my other endeavors.
Just expanded clay pellets holding the starter cube in place in the cup(holder?) for the aeroponics.
Smaller seeds generally need finer soil. You can screen potting mix to get rid of bigger chunks. You can also mix in stuff like vermiculite, rice hulls, or perlite to lighten it up, too.
Like others noted, big seeds are going to be forgiving, but something small that needs to be on the surface and get exposed to light will be a bit trickier.
I’m no expert, mind you. This year I did a coir/vermiculite/perlite blend for starting tomatoes. They sprouted fine but stalled—no true leaves for a couple weeks. After adding some fertilizer tea they’re growing again. Still not sure if they’re worth keeping but I’ll give them a shot.
Next time, I’ll try the starting blend with some soil added in. They just don’t get enough nutrition from just the starting mix.
I use the same ingredient pool, and the catch to it is that you need to be giving the seeds some dilute liquid feed starting right after seeds sprout, since they get very little from the substrate itself.
You’ve got the right idea already; just saying this as a +1 nudge.
I just use liquid food when I water. All my sprouts seem happy.
To my understanding, high nutrient soils can burn baby seedlings. This is especially true for blends of peat moss with artificial fertiliser but also uncomposted/poorly composted manures.
I usually go for last years, ie depleted, soil. For small seeds i just pulverise it with my hands for the top centimeter. This year I used soil made of composted manure mixed with sand/fine gravel, crushed terracotta, charcoal and woodpulp i took from some decomposing tree in the forest.
Tomatoes, kale, cauliflower, oregano, sunflower, paprika and chili all took off no problem. No signs of life from my cucumbers and artichoke, tho I think at least the cucumber got eaten by mycelium that spread from the composted manure.
Straight potting soil holds way too much water in my experience. I usually mix some other stuff in, including perlite, so that it acts more like soil and less like mud.