Bland vegetables that contain no other ingredients, that are chopped or cut may be used provided they are insect free and are thoroughly washed before use, eg; carrots, cabbage, celery and lettuce.

Sharper flavoured chopped or shredded vegetables may not be used unless under reliable kashrut supervision. eg; capsicums, onions and radishes.  Even citrus fruits come under this ruling.

Please watch for mixed salad bags, which may contain sharp vegetables.