Not really sure what is going on. As long as you can identify the cause as contact with the cover I wouldn't worry too much about it.

It very easily could be sun burn if you've got in in an area with bright sunlight. Otherwise it could be a host of nutrient shortages. One element that comes to mind as an agronomist is potassium. This will affect older leaves, and if it transfers up the plant it would be a good indication that your soil is lacking proper nutrients. Nutrients work in very close relationship with each other so it may be hard to tell overnight! Best of luck!

Here is a link that might be useful: Protect plants from spring frost!

. . . interesting that as far as I can tell, Kristin has never left a reply on this site where she didn't leave a commercial behind. It's also pretty clear there wasn't much time spent reading the question.

Al

opal52, it has been my observation that a similar condition occurs whenever and wherever a leaf(let) touches an inanimate object -a wall, a container or even when people brush up against a plant regularly.

Thanks for your responses. It is great to have access to this forum and to good people who will share their experience.

Opal52, I have seen a very similar problem with my broccoli! I had wondered if it was heat-related, as my porch is west-facing and very hot in the afternoon, and I had even thought the leaves look "burnt" (turning yellow, then an orangey-red) but I hadn't thought about it being from contact with the container.

Mine are in very small containers right now but I'm looking for bigger ones to move them up. I'm also going to hang shade cloth over part of my porch to try to give them a break from the sun.

I'm also starting a battle with cabbage loopers, but that's a whole 'nother post, LOL.

Here is a link that might be useful: my flickr photos: broccoli (and other veggies)