Can I use the green part of leeks for stocks?

There is actually a flavour difference between the white and the green--as there is with any fruits or vegetables with colour variations. With leeks, the white is more delicate and the green more robust, which is why one tends to use the whites for stock.

Personally, I think the greens sliced up and then treated as onion rings (dust with seasoned cornstarch and deep fry) are both delicious and beautiful used as a garnish. I wouldn't use the greens in a stock unless I was aiming for a particularly aggressive flavour.

I agree the darker green doesn't take 2 hours or more. I've been using all of it chopped in a Quinoa, White Bean, & Kale Stew recipe, cooks fine. I don't distinguish individual flavors real well. But I regretted using all of it in a Potato Leek Soup recently because most of it was pureed & it gave it such a green color that family not used to eating w/more open mind was probably turned off. But I've been wondering,too why most recipes don't call for it. Good to know I'm not the only one trying to use it! :)

By all means you should do this. Do split it and wash the grit out. Sediment in there is too fine for a sieve and gelatin will make passing finished stock through muslin impossible. Plus you'll literally infuse the flavor of dirt (and whatever chemicals were in it) into your stock.

When I use onions for stock, I keep their skin on. I don't peel my garlic, I sometimes throw a whole bulb in. With tomatoes, I keep the vine in the pot! It infuses their great flavor ten fold.

If you're trying to make a vichyssoise or a warm potato-leek soup then I wouldn't recommend it as the flavour is a bit strong. But if you're making a robust stock for any other purpose, then go ahead.

I like to throw them in whole, so that I can remove them later.

I've always used the entire leek including the dark green. Why waste it? If it has a more robust flavor that is fine with me because I like bold flavors. The potato and leek soup I make says to discard the dark parts but I don't. I also puree the soup. It does come out a darker green than some people may be used to but it doesn't bother me at all. I think taste trumps the color of your food.

Yes, I always use the green parts. I only cut the very top off, about 1/4 inch or less. I use the green parts for soup and it gives it an absolutely amazing taste, much better than onions!!

I must admit I have thrown them out before. I never will again. Sliced up and simmered in chicken or veggie broth for about 40 mins., they make a wonderful soup, especially with a little heavy cream at the end.