Sounds like they are "damping off." Like you say 10 of 400 isn't a major problem, but maybe you could examine your methods. ie. Type of starting mix, watering, fertilizing, etc. The only time I had damping off problems I could swear I was doing nothing wrong, and it turns out I was overfertilizing the seedlings and killing them. There might be something about damping off in the FAQ's but not sure.

They basically snap in half, but they're still physically attached into the ground, and then die off about 2-3 days later.

%%%%%

I don't think it's damping off b'c that's seen where the stem meets the artificial mix at the soil line as a brown constricted area and seedlings keel over and it's RIP.

There was a time when either gnats of some small insects did chew the stems on mine, but not at the soil line.

Do you see any kinds of small critters that might be doing that?

Carolyn

Don't see any small critters whatsoever.

Will say that I forgot to mention that I have three varieties of tomatoes going out of the 400.

Ace 55, Cherokee Purple and Beefsteak.

Nearly all of the failures have been in Beefsteak, Perhaps so high as 90% with one or two in the others.

Might be a piece of the puzzle there, but at this stage of plant development I wouldn't suspect that it would make this much of a difference.

Not to argue with Carolyn, but damping off came to my mind immediately when I read "the stem is almost as if you tied a rubber band around it and shrunk it in tightly."

Just in case, take a look at the link below and see if this looks like what is happening to your seedlings. It has been years since I've had any damping off, so I don't have my own picture of the problem. I found this one by Googling "damping off in tomatoes" then clicking images. There are others you might want to compate yours to.

Betsy

Here is a link that might be useful: Pic of Seedling with Damping Off

This post was edited by bets on Wed, Apr 10, 13 at 10:08

Doesn't look like it but to be honest since it's been awhile since I've raised tomatoes and I don't recall these issues it could be.

Another way to describe the issue since the ones that had this problem are long dead now and I didn't take a picture. More or less when this happens, the tomato stem looks identical to a hour glass.

As if it were squeezed in tightly and there's no way for the stem to hold up the weight of the top any longer. Very stringy.

Rest of the tomatoes look like they're starting to grow strong though, stems thickening up. Still would like to know the reason though for the future so maybe I can adjust the way I do things.