I’m in Zone 4 or 5 and have just dug out my corn crop in a 10ftX10ft square. What can I plant in it now to get some produce out of it before the frost kills everything. Frost is around Oct 20, but can be earlier of course.
I’m thinking lettuce and radishes as they are quick growing and do well in the upcoming cooler weather.
Is there anything else I can consider?
Beets.
Spinach.
Broccoli, collard greens.
Is zone 4 region 2? This also mentions celery and cauliflower.
Anything that tolerates or tastes better after a frost is good. Cabbage, for example, also turnips, rutabaga.
You still have ~75 days to frost, you could even grow a short-season sweet corn in that amount of time!
Lettuce for sure. Some beans have short growing season. It’s probably too late for squash. And you might find in a garden shop some tomatoes that are already in flower and will produce fruit quickly. Radishes are fast, but you have to like radishes. Some of the cabbage cultivars (broccoli, kale) will keep on growing and even improve in flavor after a light frost. If your probably first frost in Oct. 20, then you might be able to harvest them through November.
I’m in zone 6, and getting ready to put in my fall cover crops. If this isn’t something you usually do, you might consider it. There are two schools of cover-cropping:
The nitrogen-fixing school. Growing clover, vetch, winter peas, etc. will add nitrogen to the soil by harboring nitrogen-fixing bacteria.
The carbon school. By growing crops that produce a lot of biomass and then applying the crop residue back onto the soil, you can increase the organic content of the soil.
Traditionally, I use approach #1, figuring that after growing corn, my soil needs all the nitrogen it can get. I plant crimson clover in late August / early September and yank it out in March, composting the residue. (I use sheet-composting to destroy the crop stubble so I don’t have to till.) This only works if you get the clover in early; if you wait until late September, it will be out-competed by weeds. (Clover is dormant during the coldest months.)
This year, I’m going to try growing oats as well, so that I can use the straw for purpose #2. I’m actually going to try just mixing the clover seed in with the oat seed. We’ll see if it works.
I’m in zone 6 and our first hard freeze is somewhere about October 20 on average with the first frost (that takes out tender vegetation) as early as the first week in October. So I wonder if the OP is really in zone 4 or 5 (there are websites that will identify your actual zone if you plug in the town where you live or zip code, but they may not be updated to reflect the latest USDA zone revision).
In actual zone 4 you need to get cold-tolerant crops like lettuce in the ground now, and anything that needs 60 or more days to mature is unlikely to be successful. In my zone, the earlier recommended hardy vegetables will work, along with turnips (for greens or roots) and rutabaga*.
(by the way Sigene, congratulations for having personally annoyed John Ashcroft. I take some pride in having pissed off John Connally). 
*Nyah nyah, your mother grows rutabaga!
yeah cabbage family stuff you can harvest in December. so maybe Brussel Sprouts are good.
plant spring greens that will be ready to harvest in September. Now is the time to plant a second batch of spring greens for fall salads.
It was a long time ago, and I expect he doesn’t remember. I should change my signature into something more current.