Vegetable Scraps:  These might include stalks, stems, leaves, parings, skins, chunks or leftover vegetables that are past their prime but not rotten, mushy or moldy.  I also add the last bits of frozen vegetable packages.

Base Veggies:  These are the “meat and bones” of vegetable stock.  A combination of the following vegetables should form the bulk of the vegetables in your stock pot.  Wash away dirt or grime and remove any pesticide residue, by soaking in vinegar water, before freezing.

• carrots (chunks or peels, tops, bottoms – but avoid the green feathery leaves)
• celery (ribs, stems and leaves)
• green beens
• leeks (especially the green parts discarded in other recipes; just wash well to remove grit between layers)
• onions – cooking, yellow, red, green; all kinds of onions, including small amounts of onion skins which add color to the broth
• parsnips – strong flavor, so keep to small amounts
• peas – a handful or so of peas, or the tops and tails of pea pods
• scallions or shallots
• spinach – nice to add in the last few minutes of cooking
• sweet peppers – personal preference here, as some people don’t like peppers
• zucchini – small amounts are fine

Unsuitable Vegetables:  Some vegetables will cloud your broth, while others add too much bitterness or earthiness.  Leave the following vegetables out of your stock pot:

• Members of the brassica family are, in general, too bitter.  These include arugula, bok choy, brussels sprouts, cabbage, cauliflower,  collard or mustard greens, kohlrabi, rutabaga, turnips and turnip greens
• Starchy vegetables include potatoes, pumpkins, squash and sweet potatoes

Seasonings:  I include parsley in my broth, no matter what, preferably fresh and finely chopped, but sometimes dried if that’s all I have available.  Other delectable additions include basil, garlic, marjoram, oregano, rosemary and thyme.

Each imparts a distinct flavor to your vegetable broth, so do a sample test test:  remove a ladle bowl of the cooking broth and add a smidgen of the herb under consideration.  Taste.  If it works for you (and your ultimate plans for the broth) add a conservative portion to the stock pot.  That might be a few tablespoons for fresh parsley, or just a teaspoon of oregano or thyme.  Taste again, add more if needed, and stop when you reach…delicious!

Resources:

Expansive list of vegetable choices

Make the Best Vegetable Broth at Home (or Meat, Chicken, Fish)

How to Make Vegetable Stock with Kitchen Scraps