I'm in south-central Missouri and have already planted some corn. Of course,
the day after planting, the forecast changed to include one night with a low
of 31 degrees, that will happen just about the time the corn is sprouting.
Will this hurt it? If so, would it help to cover the plot with black plastic
that night?

Also, I tried growing watermelons for the first time last year, and they did
rather poorly, in that the fruits were much smaller than normal (delicious,
though). They got enough water, so it must be something missing in my soil.
Anyone got any ideas?
1. Corn will stand a light frost. Some varieties do have germination in cold
soil, but if it emerges a light frost will yellow it for a few days but do no
permanent damage.
2. If your watermelons were delicious it probably means that you planted one of
the "icebox" type cultivars. These range from 3 lbs (New Hampshire Midget) to
about 15 lbs (Gem Dandy). Full size watermelons usually do not have good flavor
when under developed. To reach full size they need space 10 ft spacing on 20 ft
centers and a loose preferably sandy soil. They are not particulary heavy
feeders, but manures will help. If you have a heavy clay soil you will have to
work at amending it and to a depth of at least two feet.