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Growth halted at the cotyledon stage

Posted by PaulNS NS zone 6a (My Page) on
Thu, Mar 31, 05 at 7:54

A variety of seeds I planted in six flats - dianthus, cortaderia, thyme, Edelweiss, annual cut flower mix - all germinated speedily (within four days). Now they're about an inch high and for the past four days there has been no sign of true leaves starting. The same thing happened last year and the seedlings ending up dying. (I never had trouble starting seeds before that). The only difference is that last year I made my own soilless mix, while this year I used ProMix hoping to not repeat last year's disaster. I'm using 40w bulbs 2" above the trays. Sterilized trays and pots with bleach water. Room temp is 64-68'F. Fans are on. No damping off.

Any ideas? The only logical explanation I can come up with is that I am cursed.

Follow-Up Postings:

RE: Growth halted at the cotyledon stage

Ah ! Perhaps you ARE cursed.

Try waving a crucifix over the plants and reciting the Lord's Prayer.

Or add some bottom heat to the seedlings, they're too cold.

Please post pixs of the crucifix-waving.

RE: Growth halted at the cotyledon stage

  • Posted by PaulNS NS zone 6a (My Page) on
    Thu, Mar 31, 05 at 15:22

Perhaps I am! I'll forego the rituals though thanks. :)
I didn't think seedlings needed bottom heat, only seeds (and cuttings)?

RE: Growth halted at the cotyledon stage

It isn't unusual for the true leaves to take longer than four days to appear, so I wouldn't call in the exorcist just yet. One inch tall to the seed leaves sounds a little too much, maybe need a touch more light. Not fatal though.

RE: Growth halted at the cotyledon stage

"I didn't think seedlings needed bottom heat, only seeds (and cuttings)?"

Every life form on Earth has a Comfort Zone.

When we're too cool, we shiver, which produces heat.

Plants don't have that mechanism for keeping warm. So growth slows down.

I noticed many years ago when I was young and stupid that plants grow a lot faster in the heat of the Summer.

I stopped to think about it. And I realized that many chemical reactions speed up when more heat is available in the environment.

So, more heat, more growth.

The Winter-Sowing folks grow plants in cool temperatures on purpose. It seems that plants are evolved to focus growth underground when it's cold.

Which I suppose makes sense as the air temperatures might be 5 degrees warmer than the air.

And from a survival point of view it makes sense that the plant shouldn't put energy into above-ground growth when temperatures are risky.

RE: Growth halted at the cotyledon stage


"Sterilized trays and pots with bleach water."

What concentration of bleach did you use, and how well did you rinse it off? If your pots are clay pots, they may have absorbed a considerable amount of bleach that won't readily rinse off. The bleach would be toxic to plant roots. I don't use clay pots because they are heavy and because they provide a somewhat uncontrollable source of whatever they may have previously absorbed.

It sounds like something has stopped your plant's root growth. I use Premier ProMix BX and add extra perlite for better drainage. Use your finger or a kitchen knife or some similar tool to probe your growing medium to see how wet it is from top to bottom. If it is at all waterlogged, your plant roots may be oxygen starved.

Also, what kind of water have you been using on your flats? Some tap water can have toxic amounts of dissolved substances. Plants require a little boron as a trace element, but it doesn't take much boron to be toxic. Some trace element formulations are deliberately boron-free for use with boron-containing water supplies. Where possible, I use melted snow or rain water to water my indoor seedlings. I currently have a stored supply of both melted snow and recently caught rain water. I use tap water only as a last resort.


RE: Growth halted at the cotyledon stage

The pots are plastic, recycled from a greenhouse that was throwing them out....It's been a week since germination, the dianthus are still an inch high but a few of them have nubs. Same with the annual cut flower mix, which I don't care as much about. Guess I won't throw them on the compost pile yet. The thyme and edelweiss are tiny but have true leaves.

The mix doesn't seem too wet but I pulled a few seedlings and there isn't much root growth. Maye too wet at the beginning? We use water from a well...I started a bunch more carnations (Grenadin), adding ground eggshells and sand to the mix this time.

We get what we can at the local hardware store, and what we got for fluorescent lights was some 40W and 34W cool light, and some pinkish 40W. Maybe not quite enough light?

Anyhow thanks for your ideas and I'll post again in three days, sooner if we have lift-off.

RE: Growth halted at the cotyledon stage

if the bleach isn't totally removed, that spells disaster. any thing porous, will retain bleach.

RE: Growth halted at the cotyledon stage

Call off the exorcist I guess. They're still about 1" tall but have true leaves - at least it isn't the dread disease of last year. I've replaced some of the old lights with new Deluxe Daylight ones. I really appreciate your thoughts.

RE: Growth halted at the cotyledon stage

Sigh. It was catching, I guess.

I had to repot my earliest tomatoes because they just stopped growing.

When I transplanted, I shook off some of the soil and the roots don't look good. The deeper they go the less healthy they are.

I'll have to see if I have any seed of those varieties left and use good potting soil this time.

I bought a pH meter and it says 6.8. That doesn't seem acid enough to be the problem.

But the soil I used in that case was primarily from a batch I bought two years ago. And there'd been an acidity problem with it. Or at least a problem that amending the soil fixed.

Carrots never grew in that soil, tomatoes transplanted in were stunted.

I started checking the soil numbers and the soil I used for my later tomatoes is 6.5 !!

Goes to show, being cheap on potting soil is no bargain.

RE: Growth halted at the cotyledon stage

After a week of TLC, and daily spritzings with chamomile tea, my stunted plants are starting to green up and develop new leaves again.

Remains to be seen if the new root growth will catch the plant up for the May 20th festivities.

Stuff planted weeks later is already far past the best of the stunted lot.

RE: Growth halted at the cotyledon stage

Maybe it's the phase of the moon after all? The carnations I reseeded had true leaves last week, within two weeks of sowing. That's during a waxing moon which is supposed to encourage top growth.
I think we had the same problem as you last year Jkirk - a potting mix that was too acidic. Next year I'm going to try using well-aged compost.

RE: Growth halted at the cotyledon stage

Sixteen years ago, I took my seeds and some potting soil to a greenhouse owner out in the country. A really nice lady named Schlenther (sp?). She'd started seeds for my Father for years.

I came back at planting time and she told me in her Slavic accented English that my potting soil was 'no gud'.

She pointed to a flat with three inch high tomato plants. Then to a flat with five inch high tomato plants. And told me the short plants were in in the potting soil I had brought.

And they were six weeks older than the five inch plants !

That soil was acidic. I bought a pH meter and amended it. No more stunted plants.

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