Guinea Pigs don't need vegetables
Guinea pigs should have at least one cup of fresh vegetables each day each. Good veggies to offer daily include:
Lettuces - Good lettuces are Romaine, Green/Red leaf, butterhead/boston, curly or belgian endive, raddichio and others. Do not feed Iceburg.
Peppers - all colours, no seeds
Baby carrots - one small/medium per pig or same equivalent of regular carrot.
Chard, Red or Swiss is most commonly preferred
Corn husks and silks
Cherry/grape tomatoes (no more than 1-2 per pig)
Good every other day foods:
Celery - chopped up small plus leaves
Summer and Winter squash (all varieties)
Some fresh foods should be limited to twice per week:
Fruits - apple, plum, apricot, melon, cucumber, peach, grapes and a few others.
Herbs such as Dill, Chives, Basil, Mint, Thyme
Collard Greens/Turnip Greens/Mustard Greens
Spinach (in small amounts)
Sweetcorn on the cob
Other foods, such as radishes, banana, sweet potato and beet greens should only be given as occasional treats, say once or twice a month.
Vegetables are important to provide essential vitamins, and if provided with a good variety of fresh foods daily, there is rarely a reason for supplements of any kind to be given.