For maximum nutrition and to eat more "environmentally," try to buy fruits and vegetables during their specific peak season.
This 'vegetannual' is an imaginary plant created by Barbara Kingsolver (from her book "Animal, Vegetable, Miracle") that "bears, over the course of one growing season, a cornucopia of all the different vegetable products that [one might] harvest" in a home garden. You can 'read' this image from the bottom (May) all the way up to the latest harvestables like pumpkins (October).
It's a good start to understanding the seasonal nature of fruit and vegetable harvest.
What follows is a more specific guide to selecting fresh fruits and vegetables (source: Betty Greer, Professor of Nutrition, University of Tenn.):
FRUITS:
Apples: September – May.
- Firm to touch.
- Avoid those that are soft and mealy.
Apricots: June – July.
- Golden yellow; plump; firm.
- Avoid pale yellow or green, very hard or soft, shriveled and wilted ones.
Avocados: All year.
- Yield to gentle pressure; vary in size, shape and color from green to black
- Brown markings on skin do not lower quality.
Bananas: All year.
- Firm; bruise free; yellow touched with green.
- If needed, ripen at room temperature.
Berries:
Blueberries: June - August.
- Firm; plump; full-colored; bright, clean, fresh appearance.
Cranberries: September - December. March - July.
Strawberries: June - August.
Cherries: May - June.
- Fresh appearance; firm; good size for type of cherry.
Coconuts: September - March.
- Good weight for the size; milk inside still fluid. If no milk, coconuts are spoiled.
- Avoid ones with moldy or wet-looking eyes.
Figs: July - September.
- Fairly soft to touch. Use at once, spoils quickly.
- Sour odor indicates overripe fruit.
Grapefruit: October - June.
- Firm; well-rounded; heavy for the size; smooth textured.
- Avoid coarse, puffy, rough-skinned fruit.
Grapes: June - December.
- Fairly soft; tender; plump.
- Well-formed clusters with green, pliable stems.
- Darker varieties are free of green tinge; green grapes have a slight amber blush.
Kiwi: June - August.
- Soft to touch, like avocado.
Lemons: All year.
- Fairly firm; smooth and glossy-skinned; heavy for size.
Limes: May - October.
- Heavy for size.
- Green variety more acidic than yellow.
Mangoes: April - August.
- Solid and not too soft to touch.
- Can vary in size from a plum to an apple and in color from yellow to red.
- Smooth skin often speckled with black.
- Green mangoes are sometimes used in cooking.
Melons:
Cantaloupes: May - September.
- Color and aroma best guides.
- Delicate aroma; thick netting that stands out; yellow-tinged skin under the netting.
- No evidence of stem at blossom end.
Casabas: July - October.
- Buttery-yellow, wrinkled rinds, lengthwise furrows.
Crenshaws: July - October.
- Yellow-gold rind; pleasant aroma.
Honeydews: February - October.
- Creamy, yellow rinds; pleasant aroma.
Persians: July - October.
- Thick webbing; gray-green to brown skin under webbing.
Watermelons: May - August.
- Dull surfaces with cream-colored under- sides; symmetrical shape.
Nectarines and Peaches: June - September.
- Skin color white or yellow with a red blush.
Oranges: November - June.
- Heavy for size; firm; skins not too rough.
Papayas: All year.
- Greenish yellow to full yellow in color.
- Flesh gives slightly when fruit pressed in palm of hand.
Pears: August - May.
- Yield to gentle pressure at stem end.
- Color ranges from creamy yellow to russet.
- Ripen at room temperature.
Persimmons: October - January.
- Firm; shapely; plump; orange-red color; attached stem cap. Handle gently.
- Looks like a large red tomato in shape and firmness.
Pineapples: February - August.
- "Piney” aroma; golden yellow; slightly soft.
- Ripe when leaf is easily removed.
- Green fruit may not ripen properly.
- Over-mature fruit may show soft watery darker spots on the base or sides.
Plums: June - September.
- Plump; full-covered, soft enough to yield to slight pressure.
- Softening at tip is usually a sign that fruit is mature.
- Avoid shriveled and hard plums.
Pomegranates: September -November.
- Thin-skinned; bright purple-red; looks fresh.
Tangerines: November - January.
- Deep orange or yellow; glossy skin.
Tangelos: January - October.
Loose skin. Overripe fruit has puffy, dry skin.
VEGETABLES:
Artichokes: March - May.
- Heavy, compact, plump globes.
- Large tightly closed, fleshy leaf scales.
- Good green color. Heavy for the size.
Asparagus: March - June.
- Tightly closed buds.
- Straight, tender, rich green stalks.
- Open tips and angular or ridged spears are signs of over maturity.
Beans
Green or Wax: April - October.
- Crisp, long, straight, blemish-free pods.
Limas: April - August.
- Bright color for the variety. Crisp, dark-green, well-filled pods.
Beets: June - October.
- Firm, round, smooth, deep red-colored roots.
- Fresh-looking tops.
- Avoid those with long roots and rough, scaly areas on surface, because they are tough, fibrous and strong flavored.
Belgian Endive: October - May.
- Firm without bruises.
- Color should be white with greenish cast.
Broccoli: October - May.
- Firm, closed, dark-green florets.
- Firm, tender stalks.
- Yellowing green-colored heads of broccoli are over mature.
Brussel Sprouts: October - November/
- Miniature, compact, bright-green heads.
Cabbage: All year.
- Well-trimmed, solid heads. Heavy for size.
Carrots: All year.
- Firm; bright-colored; smooth; clean; well-shaped.
- Avoid rough, cracked or green-tinged roots.
Cauliflower: September - November.
- Bright-green leaves enclosing firm, closely packed creamy-white curd or florets.
- Avoid bruised or open florets.
Celery: All year.
- Fresh, crisp branches. Light green to green color.
- Should not have wilted, rough look or puffy feel to the stalk.
Corn: May - September.
- Fresh-leaved, green husks.
- Plump, milky kernels.
- Avoid cobs with small or large, dented or shrunken kernels.
Cucumbers: May - August.
- Bright, shiny green; firm; well-shaped.
Eggplant: August - September.
- Firm; heavy; smooth; even dark purple.
- Free of bruises or cuts.
Lettuce: All year.
- Fresh green leaves with no wilted or bruised areas.
- Heading varieties of lettuce should be medium weight for size.
Mushrooms: November - April.
- Dry, firm caps and stems.
- Small brown spots or open caps are still good in flavor.
Okra: May - September.
- Tender, bright-green, bruise-free pods, less than 4 1/2 inches long.
- Pale, faded, hard pods are tough and fibrous.
Onions: All year.
- Well-shaped; hard; small necks.
- Dry, papery skins.
- Free of green spots or green-depressed leathery areas.
- Crisp green tops. Two- to 3-inch bleached-white roots.
Parsnips: October - April.
- Small to medium size; smooth-skinned; firm.
- Decay and bruise free.
Peas (green): April - July.
- Well-filled; bright green.
- Swollen, light-colored or gray-flecked pods contain tough, starchy peas.
Peppers: All year.
- Good shape; firm exterior; thick flesh and bright, glossy skin.
Potatoes
White: All year.
· Fairly smooth; well-shaped; firm.
· Free of most blemishes.
· Avoid bruised, sprouting, shriveled or green-tinged.
Sweet: September – December.
· Thick, chunky, medium-sized with no bruises or decay.
· Should taper at the end.
Radishes: May – July.
· Medium-sized (3/4- to 1-inch diameter)
· Good red color; plump; round; firm; crisp.
· Bright-green tops.
Spinach: March – May.
· Large, bright, blemish-free leaves with good green color.
· Yellowing indicates the start of decay.
· Avoid leaves with coarse stems.
Squash
Summer: June – August.
· Bright color; smooth, glossy skin.
· Heavy for the size; firm; well-shaped.
Winter: September – November.
· Heavy for the size.
· Hard, good-colored, unblemished rind.
Tomatoes: May – August.
· Well-formed; blemish-free; plump.
· Overall rich red color and slight softness.
Turnips and Rutabagas: September – March.
· Small to medium size; smooth; firm; heavy.
· Few leaf scars at top and few fibrous roots at base.
· Purple-tinged white ones are turnips.
· Yellow-skinned, larger roots are rutabagas.