And I would disagree. Tomatoes are pretty intolerant of nighttime temps below 55F. Won't kill 'em but it will set them back. If your poly greenhouse is unheated, I'd provide some protection. Stringing some Christmas lights can help....mulching won't do much as it is the top growth that is most affected. Or try something like the Wall o' Water season extenders intended for tomatoes.

Can't even think about overnighting or planting out tomatoes here until the end of May!! Neither the soil nor nighttime temps come anywhere close to being suitable until that time.

Maybe cover them with plastic?

I'm sorry I forgot to mention that I'm growing them overseas on the Balkans. Season here starts in March for those who plant in unheated greenhouses. Temp fluctuations are going to end soon though.

@edweather The potting soil used was mix of garden soil sterilized with boiling water and Potassium Permanganate(Condy's Crystals), commercial mix(slow NPK, perlite, peat and so on), egg shells, bones, coffee grounds, wood ash. Each container has a good drainage with river rocks and tiny holes on the walls.

It's not so much the soil temps that are of concern - container soils are not governed by the same factors as inground soil and they do not fluctate nearly as rapidly as ambient air temps. Plastic or glass cloches can raise the temperature as much as 15 degrees, so that is another option (very similar to the effect of the wall o' waters).

when tomatoes are properly acclimated, they're fairly hardy and will survive 40F without much issue except for sluggish growth until temps are above 55.

you say they're in buckets.. is it not feasible to bring them indoors for the night?

@gardengal48 My bad, I was answering the first person with the soil question. I decided to cover them with a black plastic blanket for the night. Hope they make it.

@stevie There are 20 containers and I don't have free space for them indoors.

John - do be mindful to keep the plastic from touching the plants. The freeze will go right thru the plastic to the leaves.

I had to plant my tomatoes into their forever big pots. We have had nights in the 40's and there's not a thing I can do about it. So far they are doing quite well.... even blossoming. I don't know exactly where your plants are exactly -- near the house or out in the open. Mine are in a fenced-in courtyard near the stucco house so there is lots of heat retention and I don't think the area gets anywhere near as cold as they do in an open field/area.