First up, my go-to source whenever I'm wondering "Should I buy organic?" is The Environmental Working Group (EWG).

Every year the EWG publishes a list of the most pesticide-ridden fruits and vegetables. According to their website:

"EWG publishes its annual rating of conventional foods with the most and least pesticide residues to fill the void left by the U.S. Environmental Protection Agency, which has largely failed to tell Americans they have a right to know about the risks of pesticide exposure and ways they can reduce pesticides in their diets."

Fruits & Veggies With the MOST Pesticides:

Here are the most contaminated fruits and vegetables according to the EWG:

• apples
• strawberries
• grapes
• celery
• peaches
• spinach
• peppers
• nectarines
• cucumbers
• cherry tomatoes
• snap peas
• potatoes

Each of these foods had high concentrations of pesticides compared to other produce items. A few things to note:

All imported nectarines and 99 percent of apples tested positive for at least one pesticide residue.

Potatoes had more pesticides by weight than any other food.

A single grape sample contained 15 pesticides.

Single samples of celery, cherry tomatoes, imported snap peas, and strawberries showed 13 different pesticides apiece.

Leafy greens like kale and collard greens as well as hot peppers were not on the Dirty Dozen list but were found to have insecticides that are toxic to the human nervous system. EWG recommends that people who eat a lot of these foods buy organic instead.

Fruits & Veggies With the LEAST Pesticides:

The "Clean Fifteen" is a list of the produce with the least amount of pesticide residues and includes:

• avocados
• sweet corn
• pineapples
• cabbage
• frozen sweet peas
• onions
• asparagus
• mangoes
• papayas
• kiwis
• eggplant
• grapefruit
• cantaloupe
• cauliflower
• sweet potatoes.

Avocados were the cleanest: only 1 percent had pesticides. Also, 89 percent of pineapples, 82 percent of kiwi, 80 percent of papayas, 88 percent of mango, and 61 percent of cantaloupe had no residues. Pretty sweet!

When to Buy Organic: 

Harriet Tubman was once quoted as saying, "we out!" and I feel the same when passing these fruits and vegetables in the grocery store. So, I recommend buying organic if your budget allows it. Here are the 20 most contaminated foods.

1. Apples
2. Strawberries
3. Grapes
4. Celery
5. Peaches
6. Spinach
7. Sweet Bell Peppers
8. Nectarines (imported)
9. Cucumbers
10. Cherry tomatoes
11. Snap peas (imported)
12. Potatoes
13. Hot peppers
14. Blueberries
15. Lettuce
16. Kale/collard greens
17. Plums
18. Cherries
19. Nectarines (domestic)
20. Pears

Lord (or ceiling cat?) have mercy! Because wellness programs like WW and Noom list these on their "green" food list, you'd assume they are really healthy, right!?

When to NOT Buy Organic:

Generally speaking, the thicker a fruit or vegetable's skin, the less you have to worry about pesticides tainting it. Here are the EWG's "Clean 15":

1. Avocados
2. Sweet corn (note: most corn is genetically modified so I still buy organic when possible)
3. Pineapple
4. Cabbage
5. Sweet peas (frozen)
6. Onion
7. Asparagus
8. Mangoes
9. Papaya
10. Kiwi
11. Eggplant
12. Grapefruit
13. Cantaloupe
14. Cauliflower
15. Sweet Potatoes

Hope this helps you make smarter decisions in the grocery store!