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I grew spearmint from seeds that came in a amazon hydroponic kit (i.e. who knows how authoritative the labeling was). It grew well, I transplanted it outside, it is a mint flavor but very weak.

I was at a nursery (well known and reputable) today and bought a pot of Spearmint. It is MUCH stronger, and looks very different. Almost so strong I wonder if it is Spearmint since my understanding it is not overly strong (e.g. compared to Peppermint).

And looking at the images compared to those online I remain even less sure. Would anyone care to opine?

Here are leaves of the seed origin plant:

Seed front Seed back

Here are the same for the nursery plant:

enter image description here enter image description here

Update 7/6 by request a clean cut on the stem vs what I originally posted. The seed plant is on the right top, the nursery plant on the bottom left. Both were taken from larger steps in the middle of the growth.

Stem clean cuts

As to the growing conditions: the from-seed was germinated in October 2020, transplaned late in 2020, and so has been growing in a pot outside (S Florida) since. It grows in very long somewhat fragile stems, which wilt quickly with just brief dryness. A light touch yields no menthol, you have to crush it pretty hard to get a good odor. It has never flowered. It does best in bright sun (I had it in about 4 hours a day and it grew slowly, moved to 7 hours or so and it had a growth spurt).

The nursery plant is small, in a pot of about a pint and with stems up to about 5" in length. A light touch yields a strong mint odor immediately.

My mention of menthol levels was based on numerous postings listing Spearmint as 0.15% vs 40% for peppermint ([Example link no idea of accuracy])6

Additional update 7/6 whole plant view, from-seed on left, nursery on right. Note the dark (dying) sections of the from-seed are new, the landscaper cut off all irrigation in prep for the tropical storm and I didn't water for a couple days. It faded VERY quickly with much of the core (not tips) turning brown/black. The tips wilted but came back quickly with water.

Overall plants, from-seed on left, nursery on right

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  • There are dozens of different plants that are in the spearmint family, with varying degrees of scent and flavor. It's entirely possible both plants are spearmint. Growing conditions and maturity might also affect the scent and flavor; presumably the mint grown from seed is not as mature as the plant bought at the nursery. As far as the photos above go, I would think a clean cut across each stem would be more useful for identification purposes. Other information would be the growing habit of each and whether you can find rhizomes underground. Jul 6 at 0:07
  • I've added the requested image . I wouldn't recognize a rhizonme vs a regular root probably. I will likely remove the old from-seed and replace it, if I see anything clear will update.
    – Linwood
    Jul 6 at 16:59
  • Thanks...I find the info in the post much more useful now. Though, it may still be hard to provide a definitive answer. The stems are both consistent with the square shape one would expect from the mint family though. So it's entirely possible they are both mint, and it's just that the nursery one is superior. At the end of the day, what really matters is whether you like the plant or not; if the from-seed one doesn't provide the mint experience you want, till it under. :) Jul 6 at 17:05
  • Indeed, and I will almost certainly replace the from-seed variant as it is very weak (Mojitos end up very green from all the mint needed). But I remain curious what they originally sold me. Replacing it also will let me get rid (at least for a while) all the mealy bugs that have infested the from-seed one. I think I may have to give in an use something on it (always hesitant on stuff I eat).
    – Linwood
    Jul 6 at 17:10
  • "I remain curious what they originally sold me" -- even an expert will probably need more than just one leaf and the stem to ID. If it ever flowers, that will help. Photos of the whole plant, including root structure, would help. DNA testing would be definitive, but may be prohibitively expensive for your level of curiosity. :) Jul 6 at 17:14
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The nursery plant looks like spearmint to me. Our spearmint was just as strong as our peppermint (I've never heard that it's supposed to be weaker, either); it just had a slightly different flavor. I don't recognize the plant you grew from seed as being spearmint; I'm not even sure if it's in the Mentha genus. It's possible it might look different when it's more mature, if it's not already fully mature.

There are probably lots of different kinds of mint masquerading as spearmint, though.

I would far and away trust the nursery over an Amazon seed vendor.

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    Thank you. The only hesitation I have is the various topics (I added a link to one but google finds a lot) that peppermint has like 80 times the menthol, and this nursery plant is very strong.
    – Linwood
    Jul 6 at 17:00
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    @Linwood There are more flavors in mint to make it strong than that of menthol. Spearmint is high in things that peppermint isn't, and vice versa. I'm not saying my answer is definitive; it could I use some work. Jul 6 at 21:47
  • Your seed-grown mint does look like it's in the Mint family, whether or not it's in the Mentha genus. Jul 6 at 21:55
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Looks to me like you have some variant of wild mint, also called corn mint or field mint. Definitely not going to be as strong tasting as a cultivar bred for mintiness.

It's cheap, but may have been smart for the hydroponics supplier--they're known to do well in wetlands in the wild.

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