How small are the tomato plants? It could be mice; mice love seedlings. Mice also have the behavior of hiding their "catch" under things like bushes, mulch, etc. They seem to create a little cache of their ill-gotten "treasures".

I guess it could also be cutworms, which effectively cut off stems close to the ground. Some folks put barriers around the stems of the plant to guard the stem from cutworms until the stems are thick enough to fend off an assault. Once the plants have grown and the stems have thickened, they are no longer vulnerable to cutworms.

I've got to say that I've never had a problem with cutworms, but have had problems with mice on occasion. If you're finding bits of plants that look like they were intentionally hidden, especially under nearby bushes (or bushy plants), I'd suspect mice.

If your plants are more than a foot tall and getting thick and robust, then it's probably not mice. They seem to like small plants with thin stems. And they really like low growing flowers, especially marigolds and new guinea impatiens. It looks like someone came along and cut off the plants and flowers with scissors. It only takes one mouse to do that sort of damage. They're little demons.

Well, that would almost certainly explain it. The seedlings are all just a week or two in the ground and are very thin still. At first it seemed like it had to be a rabbit, because I didn't see any plants left after the first few were killed, and the physical barriers weren't in place yet.

As we've gone on (and in total including the replants I'm up to almost two dozen seedlings killed) I started to see either the plants dragged somewhat under the mulch or just gnawed off and left on the ground.

At least I've got two Cherokee Purples, an Anna Russian, an Eva Purple Ball and a Matina I didn't give away left in reserve. I think I'll plant them in pots just to make sure I have SOME tomatoes this season. I think there are 10 left in the garden at this point, although I didn't check again this morning.

The latest attempt was to put some 5/8 inch vinyl tubing around the stems up to the first leaves, and then the next morning I found another one chopped off right at the top of the tubing. (That, and the fact that earlier seedlings were completely gone rulled out cutworms in my opinion.)

I guess I'll set out some mouse traps in the garden and see if I get any results. The worst that can happen is that I kill a few mice that weren't eating my plants, and I think I can live with that.

There are several threads about large earthworms like night crawlers dragging pieces of live plants into their burrows. How big were the seedlings you are talking about, age and height and stem thickness?

The seedlings are anywere from 2 days to 2 weeks in the ground, making them 8-10 weeks old. Some of the plants were very frail and others were pretty tough. As we've gone along, the plant killer has moved higher on the the stems.

My most recent attempt, which was right before the mouse theory here, was to put a small cone of plastic rabbit fence around each plant. It created about a six inch diameter circle around the 11 remaining seedlings. I figured that if it is a small rabbit, I would either keep it out or at least be able to see the way the animal got around the barrier. I'm down to 9 plants now. two more have been cut off right above the 8 inches of vinyl tubing that I put on the protect the stems. There was no visible disturbance of the cone. It's like it either came down from the sky or up from the ground.

I planted the remaining five seedlings in large pots and put them by my front porch. At least they'll get me a few nice tomatoes this season, but it looks like I won't be needing my canning supplies in August.

As for next year, I'm going to start working on a plan for some sort of wire mesh cones that will be burried in the ground around the plants. If it is a mouse, it is more than likely that this particular one will be dead by this time next year, and that others won't share it's desire to kill my tomato seedlings. However, I'll be prepared just in case.

Did you ever find out what was eating the plants? I am having the exact same issue with my tomato plants. Whole branches are just disappearing. About a quarter of the time I find the chopped whole branch next to the plant.

did anyone found put that was eating the plant. same thing is happening to me.