My spaghetti squash leaves turning yellow and wilting, new green leaves look healthy, but wilting during the day. Plant has been mulched with clean straw, and they have been watered regularly, and once a week with a 20-20-20 Miracle Grow type powdered fertilizer. 1 Tbs per gallon of water. No weeds near base of plant. Bare vine by base, but no rot. The set squash all look fine and seem to be growing well in spite of the wilting leaves. They look better in the morning, but not great, and are all wilted by evening. Any suggestions?
Without pictures, it would be hard to say. Knowing that you feed so often with a high potency fertilizer tells me that it is being drastically overfed, though. Feed as needed, to avoid overfertilization.
This articlewill help you to determine nutrient content of soil:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
your tips about leaving them out in sunlight. Would putting them under plant lights ripen them as well?
A sunny window will work better. Every source I read said they would not ripen without sun. You can try it under a grow light, but they need warmth, too, about 85 degrees F. I did find a source where a reader used a grow light but it ripened very slowly.
https://www.gardeningknowhow.com/edible/vegetables/squash/spaghetti-squash-ripeness.htm
Should I purchase squash from a better market?
There are several reasons for bitter squash. The vendor may not realize he is selling bitter squash. Here is more:
https://www.gardeningknowhow.com/edible/vegetables/squash/bitter-tasting-squash.htm