Seed Starting Troubles

Hi,
I am trying to develop my seed starting skills but I'm finding myself at a bit of an impasse. I've gotten stuck at the same early stage 3 times (I've done trials through the summer for practice, in hopes that next year I'll have the skills I need to not have the issues I had this year). So here's the story. I start high-quality seeds in Espoma organic seedling soil. They germinate wonderfully on time if not early. They live under a grow light a tad over 12 hours a day, that sits a couple inches over them. Cotyledon shows up no problem, excitement in the crowd, etc. First set of true leaves start to come in and this is where things start going wrong. Things start moving in slow motion and altogether stop. By 4-5 weeks in, I still ONLY have 1 set of true leaves and nothing else happening. Cotyledon starts to go yellow and fall off around this time, which I understand is when I should have 2-3 sets. The tomato-pepper seeds never move forward from there. Things I've tried

- The first time this happened, I assumed it was a nutrition issue given that seedling soil is nutritionally bereft. I had read that I shouldn't start fertilizing until 2-3 sets of true leaves, but given I wasn't getting there and my cotyledon was slowly going, I did a couple rounds of dilute liquid seaweed fertilizer. No change. N.B.: during this trial, the seedlings started in 4in nursery pots.

- During my second round of seed starting, same set up as above. I used a new grow light thinking I should change things up to get myself unstuck. Again, germination w/in the week, great healthy sprouts. then nothing. I had reached out to the seed company who told me to be patient and not fertilize so soon, so this time I abstained. N.B.: in this trial, I mixed it up and started the seeds in those biodegradable pot-things. My only conclusion was, maybe they are stunted from overwatering, especially in those not-so-breathable biodegradable pots.

- This led to trial number 3: This time I explicitly let the soil get nice and dry between waterings (if this sounds like a red flag to you, you'll be sad to learn that I wasn't doing that before, so it is unlikely the cause of the issue). I also used standard 1020 cells to control for dampness. I am now 5 weeks in and sad to report we are still stuck. The seedling cotyledons are falling off, and the true leaves are still smaller than the cotyledon. My Carmen peppers and mini peppers are stopped there. My stupid tomatoes have one nice true leaf and 1 teeny one, both of which are sllooowwly catching up to the cotyledon in that sad, yellow color.

I am bummed. I have read every article on the internet and can't help but to feel discouraged. I can't blame the seeds, which are germinating like champions. I can't blame the soil, which everyone calls wonderful and fantastic. I've tried vastly different watering regimens so it's hard to imagine that's the issue, same goes for type of container the seedlings are growing in. No white lacy fungal growth on the soil either... I don't know what to try differently. I feel stuck and I would love some advice, because I have so many seeds I dream of buying this winter but I can't commit to that cost if I can't even show success with one seedling. Please help me get a second set of true leaves.

Of note: back in winter-spring, I also started some brassica seeds that trended similarly, but they went in the ground and did... ok? at best. I started squash in 6in containers, following the same method, and those did perfect, actually got another set of true leaves and then some.

Heating mat: used throughout during the first test (it was chilly back then so I thought the temp might be giving me trouble, but issues still happening now deep into the summer). Used mat for germination only during the second test. Not used during the third test (not needed, midsummer with no AC in Boston, it's comfortably 80F in that area of the house. Germination was successful regardless). No difference found between the three trials.
Most recent Light: 2 T5 lights, 5000 Lumens and 6500K, full spectrum

Thank you so much for the help!

This message was edited Aug 22, 2021 2:00 PM

Hi apj,

Those cells look awfully small. I would never use anything smaller than a 3-inch square pot for a seedling. However, your 4-inch nursery pots should have worked fine.

That Espoma organic seedling soil might be suspect. I use Premier ProMix, and it works fine. It is a "soil-less" product. I am NOT an organic gardener, so I get a bit suspicious when that word is used.

" This time I explicitly let the soil get nice and dry between waterings (if this sounds like a red flag to you, you'll be sad to learn that I wasn't doing that before, so it is unlikely the cause of the issue). I also used standard 1020 cells to control for dampness. "

I advise you to stop using cells and start using pots. I use 3-inch square plastic pots and I will probably convert to the extra deep version of them this Winter. Don't let your medium get completely dry. Plant root hairs die when dry, and it is the hairs that absorb water and nutrients.

" I did a couple rounds of dilute liquid seaweed fertilizer. "

Well, I have no idea what is in that seaweed fertilizer. But you shouldn't be having this much trouble. What are you using for water to water your cells with?

" I have so many seeds I dream of buying this winter but I can't commit to that cost if I can't even show success with one seedling. Please help me get a second set of true leaves. "

You should get way more than just a set of true leaves. You are absolutely correct in requiring a successful methodology before committing to a big seed investment. I grow zinnias from seed to seed indoors during the Winter, so what you want to do can be done.

ZM