Tomatoes harvested ripe from the garden will keep for a week, but most refrigerators are a bit too cold. For best quality, they should be stored at 45-50 degrees F. Green mature tomatoes can be harvested before frost and stored at between 55-70 F. For faster ripening, raise temperature to 65-70 F. Mature green tomatoes can be stored three to five weeks at 55-58 F. Wrap each tomato in newspaper, and inspect frequently for ripeness.
Watermelon can be really challenging to guess when ready. I find the most reliable cue to be what is called the grounds spot, when the underside of fruit that was touching the ground turns from whitish to yellowish. The tendril at the juncture of the fruit stem and the vine usually dies when the fruit is mature. Thumping an immature melon gives a ringing, metallic sound while a mature melon gives a dull thud.
Cool, Dry (45-55 degrees F)
Onions for storage should be dug when two-thirds to three-fourths of the tops have fallen over, and the necks have shriveled. Remove tops, place in shallow boxes or mesh bags, and cure in an open garage or barn for three to four weeks. Store in mesh bags in a cool, well-ventilated location.
Warm, Dry (55-60 degrees F)
Pumpkins and winter squash are harvested when mature but before frost - the rind is hard and the colors have darkened.
Warm, Moist (55-60 degrees F)
Sweet potatoes should be harvested in the fall before frost kills the tops. Carefully dig the roots and cure for one week in a warm, well-ventilated location, 80-85 degrees F before storing.
For more information on growing and harvesting vegetables, see Purdue Extension’s “Home Gardener’s Guide” (HO-32) http://www.hort.purdue.edu/ext/ho-32.pdf.