Vegetables in new earth boxes

Question

After I set my boxes up, I bought from a local nursery: tomatoes, cucumbers, yellow squash, and bell peppers. Within two weeks the plants were HUGE! Thank goodness I had also built a sturdy 7-foot trellis on planting day. It looked like it was going to be a bumper crop. The squash and cucumber had so many blooms. Soon I noticed the green leaves became less green and their veining showed through. A friend said powdery mildew. I used the organic spray for that but then all the little fruits began to turn black. The plant never stopped blooming but the babies never developed. The base of the plant turned black also. I got ONE beautiful squash before I gave up and pulled them up. The cucumber gave either small or misshapen fruit. So my question is: is the growing medium contaminated? I’m not ready to give up on the boxes, but I hate to go to the expense of buying more potting mix if I don’t have to. I’m very new to gardening. I live in the lower coastal bend of Texas. Thanks.

Answer 1

This could be a nutrient deficiency or a pH problem in the soil. When leaves turn pale green or yellow, but the veins stay green as in the following images, it is often a sign of iron deficiency or too-high soil pH:

https://content.ces.ncsu.edu/strawberry-iron-fe-deficiency

When fruits turn black starting from the end, it can be because of a nutrient imbalance or pH problem:

https://www.gardeningknowhow.com/edible/vegetables/tomato/tomato-blossom-rot.htm
https://www.gardeningknowhow.com/edible/vegetables/squash/squash-blossom-end-rot-causes-and-treatment.htm
http://vegetablemdonline.ppath.cornell.edu/factsheets/Tomato_BlossRt.htm

A soil pH test and/or soil nutrient test could help clarify what the problem is. Or, if the boxes are quite small, the plants may simply not have enough soil to draw nutrients from.

A powdery mildew infection looks like white powder has been dusted over the leaves:
https://www.gardeningknowhow.com/plant-problems/disease/get-the-cure-for-powdery-mildew.htm