For dense vegetables (beets, carrots, potatoes, winter squash, etc.) figure 1 – 1 ½ pounds per 1 quart of stock. When making soup from leafy greens, you will need about 8-10 cups of coarsely chopped greens per quart of stock. Stock can be homemade, one of the purchased organic varieties or made from vegetable bouillon cubes. If none of these is available, don't despair, just use water.
The amount of potato to add to your vegetable soups depends on how thick you want the soup to be, but it doesn't take much. If you're making about a quart of soup with four cups of vegetable broth, one medium-sized potato will make a moderately thick soup. Bring to a boil, turn the heat down and simmer the soup for about an hour. Take the pot off the heat and let the soup cool for a while. When it's well cooled put it in the blender in small amounts or use an immersion blender to puree the soup. If you make it in larger quantities you can freeze some for those cold winter nights.
The secret of making good soup is in the seasonings. Of course some salt and a pinch or two of ground pepper is a good place to start. Thyme, oregano, sage and basil are good standard soup seasonings. For tomato soup bay leaf, marjoram or tarragon add a nice touch. Marjoram is also good in onion soup as is oregano or a combination of Italian seasonings. Grated lemon is very nice in beet soup and a sprinkling of ginger right before serving adds a tasty touch to carrot soup. Dill is lovely garnish on soups, especially borscht and cold cucumber/yogurt soup.
You can bulk up your pureed soups by adding some rice, noodles or pasta and/or some diced carrots or potatoes. Be creative, experiment and have fun.