A couple of possibilities come to mind.

First the trees. You didn't state what variety they are or how far away they are. The second possibility is worn out fertility. You didn't state your present program there...so it is hard to come to definite conclusions.

The trees are white oaks, about 150 feet west of the garden - with branched that grow out to the edge or a little over the garden - I keep them trimmed back as well as I can.

I fertilize liberally but not over much with 10-10-10 fertilizer

I do have a hard time imagining 150 foot horizonal branches!
Large trees do impact nearby gardens badly so without a soil test, they might be the problem. Check the actual distance of the trees from the garden....I do it by stepping it off.

So the oak tree literally has branches that extend outward 150 feet? I suspect that the tree isn't actually 150 feet from your garden, but probably a lot closer. Most trees have the majority of their feeder roots located at and outside of their canopy, so they can get water, because their own leaves will block rainfall. So, you may have an issue with the tree taking a bit of the nutrients from your garden. Oaks aren't particularly greedy though, so I doubt this is your problem.

On to the nutrients. You say you "fertilize liberally but not over much with 10-10-10 fertilizer. I'm not quite grasping what that actually means. More importantly would be how much, how often, and over the whole garden or not. I suspect that over all these years, you have depleted your soil of just about all of the nutrients, as Wayne mentioned. If this is the case, your fertilizing regiment is far more important than ever, because your plants may be relying on it 100%. If it were me, I would start working a heavy amount of compost and/or manure in, to try & build your soil back up. Also, you should look into applying a controlled release fertilizer along with the compost, because compost takes too long to be broken down into usable nutrients. The CRF will feed your plants while the compost breaks down. I would do this for a few years at least. Look into Osmocote Plus, which has an ideal balance of all nutrients, including the minors. It claims to work for 6 months, which is pretty much the whole growing season. I plan to use it next spring, by working it into my entire garden bed.

Joe

Sun is so important to summer crops. It's neat when the extra shade lets you get a few more weeks of lettuce/peas/etc, but it can really effect your summer crops.

It's amazing what the loss of even a few hours of sun can do for production. No amount of water or fertilizer can overcome this limiting factor.

Sorry. Typo. I meant 15 feet. I didn't mention that I can't see very well

Disease and nematodes are another possibility. Root Knot nematodes love sandy soil. If that's the problem you should notice knots on roots of some plants.

Also 10-10-10 isn't a good long term fertilizer. Too low in nitrogen and too high in phosphate. Apply some straight 21-0-0. It will supply more nitrogen and lower the pH a little. Once the pH comes into line there are other nitrogen sources like urea that are more pH neutral.

I've noticed on here that no one mentions that they rotate their crops. I have gotten poo-pooed by some when I do mention it. It is done for a reason. To help the soil recover and to discourage pests and diseases. I almost always do it. We have very little pest or disease problems. The drought and heat were our enemies this year.

Get the soil tested again.

10-10-10? WHY?

Sue

I thought 10-10-10 was standard fare for general veg gardening

I'm not against 10-10-10 and use some myself. However I like to add nutrients and organic matter for more complete feeding of both the plants and the soil.

Check how many hours of direct sunlight you are getting, exactly. This has been quite a different kind of summer too.

Fertilizer NPK ratios are widely debated. From my research on the topic, I've found that the most "factual" research, meaning ones with scientific facts, say that most all plants, from trees, shrubs, flowers, houseplants, vegetables, and more, use nutrients in roughly the same ratios; 3-1-2. Sure, there may be a slight variable, but not much. Using a fertilizer with a 3-1-2 ratio will provide for everything you have. This would include Miracle Grow types with the numbers 12-4-8 and 24-8-16, which are very popular. Using a fertilizer with 10-10-10 provides too much phosphorous and potash, which will go to waste, or accumulate in the soil. Beware also that most fertilizers don't contain ALL of the trace elements like calcium and magnesium, which are essential for plants. Compost will cover that, especially leaves.

Joe

Micronutrient exhaustion could be another issue. Copper deficiency is one associated with stunted growth. I usually replenish them with wood ash, but since you have high pH, you would have to do it with large amounts of organic matter. And yes, lay off the P for a decade or so.

To elaborate on the P. Tomatoes need 3-1-6, collards need 4-1-2 (or even 5-1-2). Beans may need 0-1-3. A general purpose long term fertilizer will have much higher N and K than P. On top of that, your sandy soil leaches N and K, but is relatively more P retentive. Testing is really a good idea.

Very interesting. I thought 10 10 10 was THE standard veg fertilizer. I am humbled. Is the 21-0-0 readily available?

I am getting 8-9 hours of direct sun on a sunny day now.

Actually, beans, cukes, and vining trellisable squash produce jungle like foliage but few fruits

Urea is readily available (46-0-0) at an agricultural supply store. I bought 50 pounds sometimes around 2000, I have maybe 10 pounds left.

If he had been anywhere in the south, I would have believed 150' spread on an oak. I've seen some pretty big ones in my life.

I'm betting it's micro-nutrients that are missing.

And yes 10-10-10 WAS the prescribed fertilizer for a long time but it's not the '70s anymore and we've learned the error of our ways. They are really discouraging anything but nitrogen down here.

If fruits are lacking, but there is good foliage, it could be boron. Or it could be excess of one macro-nutrient, P or Ca according to the PO original description, blocking absorption of a micro-nutrient. Again, a good test will help.

Bloodmeal is 12-0-0 and I've seen it everywhere including walmart, pikes nurseries and home depot. It's a little on the pricey side but a good choice for organic nitrogen.

The poster reports good growth on vines. I would suspect magnesium shortage. The effects of long term use, and a shortage of micro nutrients.
I would suggest a course of Epsom salts, with 4 ozs of white vinegar per 1 gallon of water.
This will help with the magnesium, and the vinegar will lower the .pH somewhat.At the same time lots of compost, or even better Activated Compost Tea.

I really appreciate the advice all