Moisture and heat are two factors that work for tomato seed germination, providing seed is fresh and source is reliable.

Agree, Probably moisture too low. Also @ 70F it will take maybe twice longer than @ 85F.

Another point: You don't need light before germination.

Seysonn

Moisture definitely not the issue. Light is on because the tray next door does have seeds that need light for germinating, all of which germinated fine and are clipping right along. Probably just too cool, but this is how I have done things for 10 years and never had a problem, usually they are up within a week. Eh, the vagaries of gardening.

Even though I've managed to nail things down well enough that I get really good germination (and don't dare change), the past still whispers its guarantees of doom in the back of my head, so I plant lots, plant in waves a few weeks apart, and end up with a ridiculous amount of excess. I know that as soon as I get complacent: whammo!

You know those stories about people leaving baskets of zucchini on doorsteps at three in the morning? That's me, in the next few weeks, with tomato and pepper plants.

I grow a ton of extra plants for neighbors, coworkers, friends, and market, so I'm rarely without them come main season. These were earmarked for early production in my high tunnel. I don't plant many extras this time of year because nobody wants them yet, and I can't bring myself to compost good plants. I usually find somewhere to shoehorn them in. I went ahead and started a new tray, so if murphy the lawman is lurking around, both trays will spring into action and I'll be buried in plants.

Sounds like old or improperly stored seed.

Sounds like you missed the "fresh seed" part of the OP's message.