What has killed my plants?

I've lost two bed in just over 36 hours and I am trying to work out what on earth went wrong before I replant.

One bed contained three kiwi plants - different varieties that I've had for 2 years. The neighbouring bed had seeding tomatoes, basil and marigolds that had been in for two weeks having been grown under glass.

The tomatoes and basil appear to have just gone, the marigolds look more like crispy fried seaweed and all the kiwi's leaves have lost their colour and have gone limp and will probably drop in the next day or so. I believe they were all bright green and happy yesterday morning when I did the watering, this evening everything is devastated.

Any ideas what can do this? - fungus, over watering, herbicide? And are there any test I can do to verify?

Perhaps, but the kiwi's had survived winter.

Frost for the tomatoes & Basil for sure as for the kiwi was it sunny when you watered & did you water the leaves? If so the sun will have scorched them if it was hot enough. You might find the kiwi will regrow, I assume it didn't have leaves over the winter & they were new leaves, so very tender

Wood chip on the kiwi's was new-ish (3 weeks+ or so ago). The tomatoe bed did have compost from the allotment added, which may have been of dubious quality as some of it was from before my time.

It is the speed at which everything went which took my by surprise - and it only seemed to affect two small beds near the middle of the plot, so yes probably frost/ cold related as others have said. The lemon balm in a pot less that 10 feet away, but in a slightly more sheltered spot was unaffected for example and the strawberries on the other side in a more exposed spot seem to be as happy as ever along with other seedlings like radishes

The council in our area use a lot of lime for the compost they make, so that can be an issue.