Garden plants - can my horses eat them?

Our vegetable garden has been overrun by grass. So I'm wondering if I can let my horses out in it to eat the grass, the only problem is the leftover vegetable plants that are in it. Will the plants hurt them?
I recently found that tomatoes are harmful to horses (by the way is it just the tomatoes themselves or the entire plant?).
Here's a list of the plants we have in the garden:
- potatoes
- beans (variety some green and some navy or northern, I think, maybe others
- cucumbers
- squash
- zuchinni
- beets
- carrots
- onions
- radishes
- peas (I think they're sugar snap)
- green peppers
- banana peppers

I think that is all, except for watermelon and cantaloupe, but I don't plan on allowing the horses access to them, but are they okay if they do get into it.
Also are sunflowers okay? We have some bordering the garden.

Thanks so much for your help.

Not sure about all the plants, but tomato plants are poisonous to people, too- not the fruit, just the leaves and stems and such. Most animals won't eat them anyway, since they taste very bitter.

Please do not turn your horse out into the vegetable garden!! It's not worth the risk of making your horse very sick and possibly get poisoned by some of the plants.