By Alexandra Sifferlin
August 6, 2015

In August, Farmers’ markets can offer an embarrassment of riches, thanks to long, hot days that produce extra-flavorful food. But choosing what to buy among heirloom, vine-ripened and organic varieties–and that’s just the tomatoes–can be confusing. Recent data suggests that Americans are increasingly selecting the latter. Organic-food sales in the U.S. have swelled to $35.9 billion a year, and producers are required to abide by strict rules enforced by the Department of Agriculture. But since organic food is often costlier, is it worth the splurge?

That depends on your budget and how concerned you are about having synthetic pesticides, which are generally prohibited in organic farming, in your food. Some pesticides can be harmful to human health, according to the Environmental Protection Agency, though their effects–and in what quantities they pose harm–are largely unknown. For now, the peak-season foods listed below are the ones for which conventional varieties are shown to be higher in pesticide residue, according to 2015 research.

CORN

There’s no produce more evocative of summer than corn, and August is peak season.

Buying tip: Purchase corn as close to its source as possible. Long shipping times can reduce sweetness.

Organic or Conventional?

Conventional

TOMATOES

Tomatoes need many hours of light and hot days to develop their flavor, so now is the time to fill up on them.

Buying tip: For ripe tomatoes, look for bright, shiny, firm skin that has a little give when squeezed gently.

Organic or Conventional?

Organic

SUMMER SQUASH

Yellow squash, zucchini and pattypans are all in season now.

Buying tip: A flavorful summer squash is smooth on the outside and typically small or medium in size. It can last in a refrigerator for up to a week.

Organic or Conventional?

Conventional

Cucumbers

Although they are available year-round, cucumbers are at their most crisp and fresh in August.

Buying tip: Avoid cucumbers that look swollen or feel mushy. The length and diameter don’t matter.

Organic or Conventional?

Organic

OKRA

Okra peaks in August and September.

Buying tip: Look for small green pods and steer clear of bruising. (Okra can get slimy when overcooked, so follow a recipe if you’re a first-time eater.)

Organic or Conventional?

Conventional

EGGPLANT

Eggplant is at its best from July through early fall.

Buying tip: The size and color can vary widely based on variety, but eggplant should be heavy and have firm, shiny skin.

Organic or Conventional?

Conventional

WATERMELON

You can get other melons year-round, but summer is ideal for watermelon.

Buying tip: Look for symmetry, a heavy weight and no bruising. Local is also ideal, since watermelon is at its sweetest when picked.

Organic or Conventional?

Conventional

GRAPES

Warm sunshine is good for grapes, whose flavors are concentrated in August.

Buying tip: Pay attention to the stem. If it’s brittle and brown, the grapes likely won’t last very long.

Organic or Conventional?

Organic

Contact us at editors@time.com.

This appears in the August 17, 2015 issue of TIME.

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