How many hours of sunlight does your garden get each day?

Everything you listed requires at least 6 hours of strong sunlight each day to do well and more is better.

The exceptions are lettuce and tomatos. Lettuce usually does OK in a somewhat shady area and tomatos will grow in part shade, they just don't yield as much and are slower to ripen.

Other than sunlight I would wonder how often the plants were watered.

There is nothing missing in the soil recipe in sq ft gardening assuming one is using homemade compost or commercial compost made from at least 5 ingredients. Some folks believe a little fertilizer for certain plants might help, but nothing should outright not grow or die in the mix.

Can you provide any more details regarding your crops? When you say the beans simply died, what does that mean? How large were they before they died? How large were the cukes before they petered out?

One other question would be what did the plant roots look like? It's a long shot, but is it possible some critter tunneled under and fed on the roots?

Would like to help you out, but I don't feel I have a good grasp of what happened at this point.

The onions are something I can take on. Onions are day light dependant, They only make the bulb when the days get to a certain length, if the days got short enought to early or more often too long too late at your latitude (and location) or if suplimental lighting or a porch light interfered you would get nothing under ground, find an onion that someone near by grew with sucess and then grow that same strain yourself for best results.

Two years ago I had similar problems -- seems like nothing survived. Lots of bugs were in my garden. It's hard to tell what the problems were- but I'm getting a soil test this year, and testing seeds for germination, before I plant them out this year-- and planning to protect my garden more by using cages to protect those tender shoots-- is your growing season part of the problem, perhaps planting earlier would help?

Do you know what your pH is ? Tomatoes seem to grow in th ewidest range of pH, although a plant grown in the wrong pH that gets 5 ft. high and provides plenty of tomatoes for an average family may get 8 feet high and you will have bushels to give away with optimum pH. Most other plants are much more picky about a pH between 6.0 - 6.5 ( for most - onions like it a bit higher )