6 to 8 hours of sun isn't enough for those sun loving vegetables. I suspect your problem lies there. Other than light, plants need water and nutrients. Good soil is also important. But, I'm pointing my finger at lack of sunlight.

Joe

not true. Squash makes it on less sun than tomatoes for example. There should be zucs on 6-8 hours of sun. Parsley makes it in almost complete shade. Potatoes are about the same as squash, and even corn tolerates some shade.

My questions are the same as ltilton's.

Dan

I live in Southern Ca., too, and the weather this year has been a lot cooler than normal, and more damp. The nighttime temps have been low, too, and that affects the setting of fruit. It has affected my summer squash more than the other plants.

I would suggest a nutrient deficiency of some sort. It's too easy to state a lack of nitrogen, but only a soil test can give a definitive answer.
For example. We had a similar problem with a slow decline in quality and size. Did a professional soil test, found it was short of magnesium. Adding Epsom salts cured the problem, now we're back to good growth.
A further note. Our Homeopathy found we were also short of magnesium, made me sit up and listen!

A further note. Our Homeopathy found we were also short of magnesium, made me sit up and listen! >

Wow! that is so fascinating and cool! Did you eat out of the garden a lot?

Surely I would be short on iodide if I were not using iodized salt. All my meat and vegetables, and 90% of my fruits, are local, and this is Goiter Belt. But for the rest, there is wood ash.

I had issues with a new bed we built this year as well. It was a raised bed so we filled it with bought topsoil and a lot of different compost. The plants were stunted and most of my spring crops never got bigger than 3-4 inches no matter how much fertilizer I added. The radishes had a lime green color to them, beets turned almost a dark red and the broccoli had a purple hue. I think the problem was that I should have let it sit for a few months. My guess is the compost we bought wasn't fully "composted" and since it contained cow manure it stole the nutrients my plants needed to finish decomposing. After a few months of sitting there, my summer plants are now flourishing. So the question is, was fertilizer the only thing you added or did you also add any compost that possibly wasn't finished?

Could also be fertilizer burn? Skip the Miracle Grow & see what happens. You can purchase complete organic fertilizer in granular form then apply before planting & no hassle all season.

Don't give up. After harvest layer on compost materials (shredded leaves, used coffee grounds, manure, spoiled hay, veg/fruit scraps, etc.).

Make sure each layer is moist & come spring your soil will be amazingly full of worms & microbes ready to grow a great garden for you!

You might doubt the compost way, but it does work & your soil can be improved with a lot of organic matter (4" of it mixed in with 12" of soil OR skip the mixing & just layer it like I mentioned).

Gardening can be easy if you do the layers & keep it up.

Mulch your soil after planting. Don't step in planting beds.
Add more compost after harvesting before replanting.
Cover with mulch any areas not planted.
Your organic matter content will be maintained with continual additions & you won't have to till it in again.

Hope that helps!