Sudden death seedlings

[rick2718]

Hi,

After an abysmal round of jiffy-soil failures, then finding and reading tips here, I have a lot of happy seedlings except for:

Collards - sprouted to tiny size ( less than 1 cm) and still there after six weeks
Poppies - sprouted and stalled also, but absolutely hair-thin, then they fall over and die
Corriander - keeps getting taller and taller until it falls from its own weight

Ive used a couple of different potting mixes, which work well for the other plants. I have a heating pad under 1/2 of them but it does not seem to matter, and I've tried both top and bottom watering.

Thanks in advance if anyone can shed some light on what mistakes i am making.

[AnnaIkona]

I've had the same problem with collards. And the solution is to give 'em more space length wise and height wise. Space them out or better yet repot th into different containers.

[applestar]

It sounds like they might not be getting enough light.

Also, while collards benefit initially from bottom heat to germinate, they are essentially cool weather crops, and the poppies and coriander/cilantro germinate and grow in cool soil. Have you measured/monitored the soil temp? The heat mat might be "cooking" them.

[pepperhead212]

As apple noted, that heat mat may be too hot. I have a thermostat on mine, and it's amazing how seldom it is on to keep the temp to 78°.

While I haven't grown collards for many years, I grow many other brassicas, and never bother to use a heat mat for those - I just plant them in small (72/tray) pots, they pop up in 2 or 3 days, and the small plants go outside in 3 weeks. I have noticed that brassica seeds begin showing signs of age at about 4 years - they are slower to come up than others in the tray, and the % goes down, as well, plus the plants simply don't grow as fast. From now on, I'll toss them after 3 years. Often there are still many left, since they are such small seeds.

[rick2718]

Thanks for the suggestion.

I have not measured soil temperature, but though the mat is on all the time, the soil feels cool... for whatever that is worth. Is there a preferred soil temperature for poppies/corriander/cilantro?
Is room temperature too much?

I have a tray with poppies sans heat, and they are doing the same as those on the mat.
They are under an 18 hour a day light. I'll try real sun when it warms up a bit more.
I will repost for others if I manage to isolate the issue(s)

[applestar]

How close are they to the light bulb? What kind of light source -- fluorescent, LED. Incandescent....

I don't think "feeling cool" is enough since it will likely feel " cool " to the touch if moist. Do you have an instant read meat/bread thermometer?
Subject: 2016 -- starting seeds and cuttings for the new season

-- time to calibrate.

When putting in sunlight, remember to gradually acclimate.

We would have a better idea if you could post photos.