I've seen soil temps of 55-60 degrees recommended for setting plants out and then a steady soil temperature after that. I think you'll be okay with 68 degrees as long as your plants are well hardened-off. I suppose it would be okay if the soil temp gradually grew warmer, but tomatoes don't do well with wild fluctuations of soil temperature. Do be aware that container soils are much more apt to fluctuate than earth-soils because of ambient heat-absorption, so keep your plants well-mulched and your containers shaded from strong summer heat.

Seems awfully early for zone 5 plant out? I did April 15th last year down here and lost several plants to surprise late freezes so am waiting till 3rd week in April this year.

Our garden soil temps are running 65 degrees right now but we have 3 days of low 30 temps coming up along with rain so that will drop the soil temps.

I prefer to wait for 70 degrees for in-ground planting. And as Anney said, soil temps in containers will fluctuate greatly.

Planting this early, I assume you plan to cover and protect them in some fashion?

Dave

Thanks for the replies guys, I probably won't plant until April 15th at the earliest and may wait until May 1st. This is my first time at planting in a Earthtainer. I always planted my tomatoes in the ground going by air temp instead of soil temp. I have planted tomatoes on April 15 and also May 1st and after a month or so I can't seem to tell any difference in the plants. I'm assuming the April ones just set in the ground waiting for the soil to warm up so that is why the one planted in May seem to do the same. Sorry but I hope that makes sence.