Deconstructing paradigms: do seedlings really need special seed-starting mix? Part two
Exciting results -- more successes with cold-processed compost and a whole lot of feedback and some photos from other seed--starting growers.
Cliff notes:
-After a few new trials, and feedback obtained from other gardeners, I am now convinced that purchasing a special “seed-starting” soil isn’t always necessary. But I’m not quite ready to go without.
-Pittmoss (a peat-free soil starting mix) does not work for me - at all. The Plentiful formulation.
This is part two of my quest to find an alternative to peat and coconut-coir based potting mixes. Part one shows my success using pure compost to start peas.
After I ran out of my last store of peat, I went over to a local ag supply company and they recommended Pittmoss. I spent the $40 on the big bag and brought it home, feeling uneasy about the amount of plastic I was introducing into the environment. I got to thinking that I would really like to find an alternative that wasn’t trucked around all over the place.
So my first experiment started with comparing Pittmoss to the only other alternative that I had at the time - cold and wet compost, unsifted. I had evicted the worms out of the compost so that I could use it indoors, but left it outside and a freak very heavy rainstorm came along.
The result was a wet, mucky mess. Normally I’d never attempt to grow in such a medium. The soil was so wet it was likely to encourage rotting. And since it was so wet, I was unable to sift it out and incorporate air, which would make for a solid clump of soil that seeds would not be able to penetrate. Or so my conventional gardener wisdom told me.
“Try it anyway!!” My instincts screamed at me. My logical brain told me that I would prove to myself why a special seed-starting professional mix was needed. But that is *not* what happened.
This first photo is of a fava bean trial. Both six-packs were started at the same time. One with the wet mucky cold compost, and the other with the commercially prepared, lightly rewetted Pittmoss.
Neither is growing super well, but one is clearly doing better than the other. The top is the cold mucky compost. All seeds eventually germinated out of this mess. The bottom is the professionally prepared commercial potting soil, only half germinated. When I looked at the puny seedlings, I found mold growing on them, even though I was careful not to water the seedlings too extensively.
The next trial I did was a tale of two True Siberian Kales from Adaptive Seeds.
Again, neither is optimal, but the difference is super interesting. On the left, we have the commercially prepared Pittmoss. All kale seeds did germinate (as usual I thinned them down to one), but are failing to grow. On the right, we have the wet mucky compost. Only one seed germinated out of this (I was surprised to get even one out of this mess) and it is actually growing. It looks a little more anemic in this photo than it is in real life, that will be easily remedied with a little liquid fertilizer.
This third photo is of garbanzo beans. I attempted to start them in the Pittmoss, but did not compare it to the wet mucky compost. After two weeks of not seeing any germination at all, I started questioning whether I had selected seed that was not viable. So I decided to soak a handful of seeds. A day and a half later, their root tips emerged so I could tell they were still viable. I then planted them in compost that had been dried out a touch and sifted.
The photo on the bottom is of the professionally prepared Pittmoss, planted about three weeks ago. Only two seedlings are barely emerging. The photo on the top is sifted compost with *uniform* germination and growing well, about 3 weeks after the Pittmoss planting.
The clear loser here, at least for me, is the Pittmoss. I did not expect to have this bad of results, and poured the bag into a garbage bin for easy scooping and storage. The ag supply company has since refunded my money, and expresses genuine surprise at how these trials went. The “plentiful” kind may be different than other formulations.
Since that time, I’ve trailed several more fava, garbanzo, lettuce, kale, and spinach in sifted compost. So far I’m getting excellent results, and will report back when the results are ready to show in photographs.
What have other gardeners had to say on this topic? I polled around multiple other gardening groups to see what they have been using for seed-starting. The initials are how I keep track of the conversations I’ve had. Those in bold are the brave growers - like me - who are trying to use no outside inputs at all and having success. Here are the notes I wrote down:
AR of HWOGPA says she uses a mix of coco coir, garden soil, compost from the garden, vermiculite, and lime.
LB of HWOGPA uses worm castings, peat, perlite, ground charcoal, and sometimes city leaf compost.
HJS of PNWWGAF says she just uses compost, homemade or bought in a bag. This year she is using composted and sifted horse manure. She adds vermiculite for lettuce seedlings, as she finds they like it on the lighter side. She says she’s heard for years that you need to use a sterile seed-starting mix, and she finds that not true at all.
CLJ of PNWWGAF says they use Opus soil with a bit of vermiculite.
VH of FGG says don’t even try to make it and mix your own, you should only use professional mixes. When I pressed further, I found that she’s a major grower of seed starts and needs a bulk quantity.
GR of GOM says she’s been using aerogarden and forrest soil.
NNS says she’s been trying with peat-free mixes and failing.
JC of MAHC says he sifts compost and saves it for seed-starting.
VS says she’s used compost with a little vermiculite.
KL of OCG says she’s using coconut coir and some with some bagged soil mixed in. She feels coco coir is a learning curve, as it is tough to rewet appropriately. She says her brassicas and alliums are doing well, but not so sure about her solanums.
CB from PNWG says she’s doing soil blocks this year and having success.
PMH from PNWG says he just used dirt from the garden this year, and so far has had 95% success rate. The tomatoes were all started 2/28, sprouted by 3/4. They were on heat mats with lights 12/14 hours per day.
DU from PNWG recommends adding a little vermiculite to compost.
AB of POG is struggling to find a peat-free mix that works for her.
RV of POG uses 1 part cocoa coir, 1 part compost, 1 part potting soil, 1/2 part vermiculite and/or perlite, with a little worm castings and a bit of azomite. She usually doesn’t fertilize her seedlings but will use a little diluted kelp if they seem to need it.
MP of SOGG has used compost with success. She’s also just used potting soil and it worked fine.
JF from GIO uses regular potting soil and it works fine for her.
TC from GIO says she uses a mix trucked in from Vermont called Vermont Fort Vee.
KC from GIO uses cold compost and it works fine for her.
SJ of SOG is struggling badly with two different bags of seed-starting mix. She says they both seem hygrophobic.
THG from PPG says he uses 50/50 planting mix from greenlands in McMinville.
LD from PPG says she uses Happy Frog and sifts out the larger chunks.
LS from PPG says she mixed up a whole bunch of bags of potting mix and her seeds are germinating fine.
MF from SWWAG says she tried coconut coir mix that she made herself, but the seeds got a really slow start.
SK of PPG uses a mix of coco coir, perlite, and compost in equal volume.
EH of EG says she uses 1 block of coco coir, a layer of perlite over the top, and down to earth 3-3-3 seed starter. Works for her.
HMB of EG says she’s had good luck starting with DTE’s peat free mix and adding extra coir and pumice to it.
LB of PPG says she’s used compost and native clay soil. It works fine for her, except that she has issues with too many critters staying in the soil. Since she uses this in the house, it isn’t desirable to having worms and whatnot crawling out.
I’m excited to find that I may be able to go without buying anything to start my seeds. I’m nervous to go fully without, as I really do want to try some new seeds this year and am afraid of failure. However, the only other peat-free alternative that I see coconut coir, and after googling, I’m not feeling very good about the environmental impact of this stuff either.
So maybe I’ll end up buying a small bag of traditional peat-based seed starting mix to make sure I get the new-to-me winter squash and melons that I’m really wanting to try this year. But I will be comparing those starts with sifted compost.
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