Apricots are harvested starting in late spring in warmer areas and through early summer. The most flavorful apricots don't travel or keep well, so look for them at farmers markets.
Avocados have a season that defies logic - they are fickle depending on their exact location. Most, however, are in season over the summer. Ripen hard avocados on the counter or speed things up by keeping them in a paper bag.
Basil grows alongside tomatoes very well (in the garden and on the plate). Look for unblemished, leafy branches without flowers or buds (the herb gets a slight bitter aftertaste after it flowers - which is part of the reason growers pinch off the buds before they can flower).
Bell Peppers/Sweet Peppers should have smooth, shiny skins (whether they are green, red, orange, yellow, or purple) and feel heavy for their size.
Beets are often sold with their green still attached when they are freshly harvested - giving you a two-for-one. Cook the greens as you would chard or other cooking greens.
Blackberries should be shiny and plump. Avoid any berries with mushy or moldy berries - these damages rot and spread fast. Rinse berries only just before eating or using them, never in advance, since they will become soggy and rot faster.
Blueberries are the only berries that have a dull, matte finish to them when ripe.
Boysenberries, like all berries, should be plump and shiny when you buy them.
Cantaloupes that feel heavy for their size and that smell like melons are the ones to buy.
Carrots are harvested year-round in temperate areas. Unusual varieties are harvested during the carrot's natural season, which is late summer and fall. True baby carrots - not the milled down versions of regular carrots sold as "baby carrots" in bags at grocery stores - are available in the spring and early summer.
Chard grows year-round in temperate areas, is best harvested in late summer or early fall in colder areas, and fall through spring in warmer regions. Like all cooking greens, chard turns bitter when it gets too hot.
Cherries are ready to harvest at the end of spring in warmer areas. Sweet cherries, including the popular Bing and Rainier varieties, are available from May to August. Sour cherries have a much shorter season, and can be found for a week or two, usually during the middle of June in warmer areas and as late as July and August in colder regions.
Chickpeas (a.k.a. garbanzo beans) are sometimes available fresh at farmers markets in warmer climates. Look for small pale green pods still attached to twisted, twirling vines.
Chiles (fresh) (a.k.a. hot peppers or hot chilies) need heat to ripen and get hot - look for them at the end of summer and into early fall.
Cilantro, like most leafy green plants, bolts (flowers) and turns bitter when it gets hot enough, so it hot climates it is in season all year except summer, everywhere else summer is the time to look for it.
Corn is best the minute it is picked from the stalk, so it is a food to look for from local growers for sure. You want tightly closed, fresh-looking husks, fresh-looking tassels, and fresh-cut stem ends. Know that organically grown corn is very likely to have a worm or two in any batch - simply pick it out, the rest of the corn is fine to eat.
Cucumbers are known for being cool - as much as 20 degrees cooler than the outside temperature. Lucky for us that they come into season in most areas just as the summer heat kicks in.
Eggplant should have shiny, tight, smooth skin and feel heavy for its size.
Fennel bolts is hot weather, but is in season in cooler climates in the summer (look for it fall through spring in temperate and warmers areas).
Figs have two seasons, but the main one is during mid- to late-summer (a second, shorter season comes in November in warm climates.
Garlic is another produce item that we forget has a season; fresh garlic is at its plump, sweetest best in late summer and fall.
Gooseberries are more often foraged than bought. These tart, green berries should be plump and fresh-looking.
Grapes ripen towards the end of summer where they grow best; the harvest continues into fall.
Green beans tend to be sweetest and most tender during their natural season, from mid-summer into fall in most regions.
Green onions should have fresh, green tops and firm, slime-free white bottoms (fresh-looking, pale roots still attached to the whites are a good sign, too).
Herbs of all sorts grow through the summer - from basil to rosemary. Always looks for vibrant leaves and fresh-looking stems.
Huckleberries are a true treat of summer in areas lucky enough to have them (Pacific Northwest, are your ears burning?). Look for plump, purple berries.
Lemongrass has a heavenly lemon-esque aroma that includes a whiff of ginger and the heady scent of tropical flowers. While it can be delicious with most anything, lemongrass is particularly delicious with chicken and seafood. Think of it as perfume for your food.
Lettuce is in season in cooler climates (and out of season in warmer ones).
Limes are the only citrus at their best in summer. Look for small, heavy-for-their-size fruits.
Mangoes need tropical heat to ripen and come into their sweet best in late spring and summer in Florida and Hawaii.
Marionberries are a type of blackberry. Look for plump, shiny berries with a deep purple hue.
Melons should always feel heavy for their size; most should have a bit of a sweet melon smell, too.