Answer: It sounds as though you've been trying to analyze all the angles... First, since you amended the soil with organic matter prior to planting, your soil should be perfect for your veggies. It will drain well and have lots of nutrients for the roots to soak up. As for the close proximity to a pine tree, I don't think that will affect your plants. Pines drop needles which, when they decompose, can acidify the soil but not to the extent that veggies will be affected. I think the real answer is simply the heat of the sun. All the veggies you've listed, with the exception of lettuce, will thrive in full sunshine providing they received adequate water. The wilting of the leaves in the hot afternoon sun is simply the plants' way of keeping cool by conserving moisture. As long as the leaves recover overnight, the plants should be fine. Your watering method may be responsible for additional wilting - hand watering every other day will only get the top inch or two of soil wet. Since the roots of your plants are much deeper, you'll need to deeply soak the entire garden once or twice a week in order to supply enough moisture to the plant roots. Either set a sprinkler up in the garden or dig some trenches that you can flood, or build watering basins beneath each and every plant. Whatever your approach, you'll want to provide at least one-inch of soil per week to your tomatoes and even more than that for your summer and winter squash.
Here's how you can tell how deep the water is penetrating - water as you normally would with your hand held hose. Next morning, dig down into the soil to see how deep the water is going. Next time it needs to be watered, use a sprinkler and allow it to run for 15-20 minutes. Next morning, dig down to see how deeply the water has penetrated. I think you'll be amazed.
So, bottom line - water deeply once each week (more in really hot weather) and see if that doesn't make a huge difference in how your plants endure the afternoon sunshine.
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