the temperature rising from a big hole like that well is probably around 55F. Cole crops, peas, spinach, lettuce, carrots and radish would grow well there.
~tom

I would be more inclined to think it was something else...How deep was your box? soil mix? water schedule? type of squash?

But I have to believe that the soil in a raised bed would be much warmer than the 55 degrees of the hole with the normal heating of a bed...It almost seems like it would improve growing conditions instead of ruin them...I know here in TX my poor veggies would love a little coolness..

If the soild temp is a problem, have you considered trying a black plastic mulch? That should heat the temperature some. I'm not sure if it is something you should leave down season long--depends on what, exactly, you're growing.

I don't think it's soil temp. If you built it on top of wood, the roots probably couldn't go deep enough and the plants faltered.

On top of wood - how did it drain? Had you drilled holes in the wood so the excess water could drain out of the soil or was it trapped in the bed where it could drown the roots? What sort of soil mix did you fill it with? Added fertilizers? Pest problems?

Dave

I think digdirt has it right! There has to be drainage or it's just a big container, which we should know, doesn't do well with regular soil it it. You'd probably do better with a deeper bed and some sort of drainage solution. Temps shouldn't be a problem since cold settles and heat rises. Hang in there, all is not lost.