Since you need something that will stay put in the soil after the organic compost decomposes, why not add some kiln-baked diatomaceous earth such as Axix or Turface. Or some Perlite or Vermiculite for water retention.

I am never sure why so many people think adding more minerals to the mineral component of the soil will make it better but all any soil needs to be better is organic matter, the part of the soil most often missing and the only one that really does provide what plants need to grow. Organic matter does get digested, decomposed, and the nutrients in that organic matter are fed to the plants growing in that soil and, over time, that organic matter will disappear if not regularly replenished. Many people seem to have a hard time grasping that concept, that you cannot just add organic matter to soil once but need to keep adding it.
Every soil can be "saved" by adding organic matter to it, unless it alrady has way too much such as you would find in a swamp.

I had planned on adding more OM as I got it to replenish that which is settled/decomposed, but the question specifically was what I could do to improve drainage. More OM might help water drain to the bottom of the trench, but since I have ledge or clay under some of the trenches, it has created a "teacup effect". While a small effect was desirable to retain moisture and reduce the need for irrigation, in a couple of areas there is too much of this "good thing" (I know it's not usually considered a good thing).

So, I can make a raised bed where all the clay is, or just plant my squash and cukes somewhere else, but what can I do with the 15ft or so of that middle row/trench? Is it too wet for cukes? Should I raise that section by adding more OM and topsoil?

I used 1" HW cloth to screen the original sandy loam (you can see all the larger rocks we picked out laying on the side of the piles). Should I throw some 1" - 3" pebbles back on the bottom of the trench (and the 6x8 area) and some unscreened sand (believe me, more of this subsoil is coarse, not fine, sand) on top of that, then put on the OM and the finer screened stuff?

I was even thinking of continuing that middle trench on to connect with the dug-out clay basin and using it as a catch basin. It's only 6 ft away, I should be able to dig it out in a day (oh my aching back ;-)).

Ideas?

As you've noticed, by mixing soil types and more organic matter than advisable, you've ended up with that "bathtub" or "tea cup" effect. Water has a tough time moving from one soil type to another efficiently and drainage tends to be impeded where sharp interfaces occur between soil types. Another consideration is that when used at too high of a volume, the organic matter also acts kind of like a sponge, holding on to excess moisture. According to the recipe you gave, you're at just over 40% O.M. by volume which is roughly twice what you need. I strongly advise you don't add any more. It's best to be at about 5% O.M. by dry weight, which is roughly 20% by volume (Of course, it varies a bit with the weight of the soil and the type or organic matter)
You won't want to plant in the low spots because, as you've seen, that's where the water goes. You could build raised beds if you like but their success would depend on the depth of the beds and what you fill them with.
With the mix you have in the trenches, adding more material of any kind will most likely make the problem worse. This is absolutely a "less is more" situation. You should simply pull out what you've got in the trenches and fill them back in with the soil adjacent to each trench, if possible. As you have noticed in the last picture, soil of uniform texture drains the best. Yes, even for the clay areas. The clay areas won't drain as fast as the sandy areas but they will drain faster than an area with soil interface issues. That is unless the clay was brought in from somewhere else and placed on top of a sandy soil at some point in the past. That would be another can of worms. I would recommend not digging out a trench. If you want to add organic amendment, use something that is already fully composted rather than partially decomposed. A good ratio would be 20% well composted organic matter to 80% native soil by volume or 1 to 4 compost/soil. Do not place the organic matter any deeper than 1 foot. In fact, you would be just fine with putting it on top and tilling it in 6 to 8 inches. A 1.5 inch layer of compost tilled to that range of depth should get you right in the neighborhood.

As an interesting trivia note you said, "While a small effect was desirable to retain moisture and reduce the need for irrigation, in a couple of areas there is too much of this "good thing" (I know it's not usually considered a good thing). "
Actually, sometimes it is. That's why they place gravel below USGA golf greens. The sharp interface from the sand to the gravel below creates a "perched water table", which retains water, allowing them to irrigate less frequently. A lot of people think that the gravel below is to improve drainage but that's not correct. They're planting grass in a straight sand. Sand drains just fine already. Retaining water is the goal of the gravel layers.

It has been extremely wet here also Best advice is to stay out of wet clay at all cost its only going to get so much worse mucking around in it

More rain this afternoon, all through tomorrow. I think the squash bed (which already looked like a hog wallow this morning, probably a swimming pool now!) is a goner. We also had standing water on the north side of the field (not amended), just too much rain these past few months! The pond is about overflowing, my dad was digging it out more today while it wasn't raining.

I did extend that middle (really wet) trench, put some of the pebbles we had screened out in the bottom, for about 7-8ft length, then put the soil/leaf mix over them again. Problem is, I thought the solution to poor drainage was to add more OM to "fluff up" the soil, so put wood chips (mostly very well decomposed, picked out a few large pieces) in, mixed it well with the material already there (careful not to stir up the pebbles from the bottom), topped with more screened topsoil to fill the trench.

We'll have to see how it is Monday. If I have to pull everything out of the trenches and start again I will - not too much rain expected Monday through Thursday! If I hadn't already paid for a spot at farmer's market I would just give up on this area for this year (DH would kill me after all the work digging!). And I've got a garage full of tomato and pepper plants!

I've got to apologize to ajsmama. When I first read the post, I thought the issue was too much drainage in sandy loam. That is why I recommended something to help retain water in addition to compost and OM. Figured it was okay since this is not the "Organic" forum.

Good thing I have already ordered my new bifocals....

Over time, not tomorrow, the organic matter you add, and you do need more, will improve the drainage of that soil. As more organci matter is added, getting the humus (resudual organic matter) level up to around 5 to 8 percent will, over time allow the excess water to flow through your clay.
In the short term adding a little bit of organic matter to clay soils can create that "bathtub affect" and cause water to pool, especially if the soil is amended in small areas. However as more OM is added and as the Soil Food Web becomes active the pore spaces between the clay soil particles will be opened and excess water will flow more freely out of that soil.

Coach - that was part of the problem, don't apologize. The north end still seemed very sandy and dry (even the south end of a couple of trenches), though the south end of 2 trenches were very wet (and one was "just right?" Cal me Goldilocks LOL).

Things may dry out a bit tomorrow - I'll take a look, as gargwarb suggested (wish my DSL hadn't gone down so I could have read that post b4 I amended more!), maybe I'll pull everything out of the trenches (at least the wet ends), throw it in the "hog wallow" (probably a swimming pool now - and half of that wasn't amended, the other side just added a little sand!) to compost for next year.

DH and I have already decided not to plant edamame this year, use the old garden area I was going to plant that in for peppers (I already started planting those Friday) and determinate tomatoes. Maybe lettuce (I have a row started) and broccoli (it's late, but the ones I have in pots look nice).

Hoping to salvage the north ends, maybe 150 row ft, for the indeterminate tomatoes and maybe sneak 4 cukes in there since the 6 I started (2 Bush Champions can go near the house) are germinating.

Might not have room for squash at all, but since I bought Raven and Early Prolific Straightneck (which I believe are both bush types), I still have time to harvest if I can squeeze a couple plants in near the house somewhere (in big pots?).

Wee B Little pumpkins can go in the pile of topsoil at the end of the trellis and I can still get an October harvest.

Better luck next year! Thanks for the help.

Here is what I see as the issue, you have an immediate need for a planting area. Your soil has a challenging mix of conditions, wet/dry etc.

Let's try to find a method that will offer both short term and long term solutions. Another option that might work for you is lasagna gardening. In addition to adding organic material that will improve the Soil Food Web in long term, it will facilitate your immediate need for a planting area. gargwarb suggested raised beds and this would be a simple and low cost way to create them. Some compost, some straw (which eventually turns into compost) and whatever other organic matter you can find.

Straw is a cheap admendment and most farmers will sell the weathered bales from the bottom or edges of the stack for less than the pristine looking straw. And that's what you want because they are already starting to break down.

Thanks coach - we really need to plant the indeterminates in this area since the trellis is built.

My plan was to plant any "bush" type peppers, toms, cukes and squash near the house instead of the edamame I had planned. No support, but no drainage issues either and soil tested just about perfect since we have been amending and gardening for years there. Also easy to water.

I still have 50 ind. toms that need to go on the trellis, 1 40-ft row (Trench 1, eastern-most) looked OK this weekend. The westernmost was ALL wet, not usable right now (after almost 2" of rain in 3 days). The middle trenches were roughly half dry (the northern half of each).

Short term solution that would allow me to use more of the area under the trellis? Dig up the aisles under that half of the trellis and mix all the dirt and amendments that are in the trenches now? Not sure about adding more OM - either straw (which I would have to buy) or maybe some old loose hay swept out of the barn (might have mouse droppings, etc. in it, pain to climb into the hayloft and try to sweep it out, even if my cousin will let me in her barn since it is about falling down).

We've already done a first cutting, no hay left but I can get manure mixed with hay (used for bedding, may be weedy) from neighbor who bought our hay.

I can also get some leaf mold (and/or shredded leaves), have a big pile of crumbly wood chips (some chunks still recognizable). What would be best, how deep do I dig (current trenches are about 12"), and what goes on the bottom, middle, and top layers before planting (will mulch after planting)? Unfortunately we cold compost and have maybe 5 gallons of finished compost in the bin, the open pile hasn't decomposed much and right now has a volunteer melon of some kind growing in it.

Thanks

Actually, today, after a day with no rain (though it was overcast), things look much better. Only about 10ft of the middle trench is wet, about 20 ft of Trench 5 is wet, and there is no longer water standing in the 6x2 area I dug out of the clay and threw sand in (though there is still water standing in the 6x4 area I just dug out and didn't amend the clay in).

My tomatoes are multiplying! Have more than 60 indies, even after putting the Glaciers in the plot near the house. 6 Speckled Romans that I didn't think would make it are looking pretty good, I forgot about the 4 Cherokee Purples, and I think there are a few more German Johnsons than I had counted on too. I'm thinking of planting four 4th of July toms near the house and using the corner posts (EMT) of the fence to support them b/c they're starting to fruit. Think I can sucker them and maybe they won't pull the fence over (kinda flimsy vinyl-coated steel stakes driven about 1ft deep, then 10ft EMT slipped over to extend the height - stakes with guy wires at the corners)?

Can I possibly plant in the trenches that have dried out today (will check Wed after rain tomorrow)? We usually get about 4.5-5" a month, but if this July is anything like last July it will be dry (part of the reason I trenched). Who knows this year? We got 1/4 of our June rainfall in 1 day last week, and 1/2 our May rainfall in 1 day last month!

If the trenches dry out to reasonable tilth (hold a ball but poke it and break apart) within 24 hours after the rain stops, will plants be OK? Or is the 2-hr test b/c plants will drown if soil is saturated for more than 2 hrs?

Maybe I can plant cukes (shallow roots) on the wetter ends? I have about 35ft x 5ft left in the middle of the plot near the house, could do bush-type cukes there but I'd still like to squeeze in a couple rows of edamame if possible.