Whether you're in it for the culinary or nutritional benefits, here is some advice for how to work with those bundles of leafy greens.
Here are a few varieties you're likely to see at the market these days, along with notes on what they look and taste like from "The New Food Lover's Companion" by Sharon Tyler Herbst and Ron Herbst.
Kale: "Mild and cabbagey flavour." The colour you're most likely to find is "deep green variously tinged with shades of blue or purple." The prominent variety is curly, although you may also come across Tuscan/dinosaur/lacinato kale, which has flatter, darker leaves, and red kale. The Kitchn and Bon Appétit agree that Tuscan is milder and less bitter than curly, although they don't quite line up on whether red kale is on the mild or more bitter side.
Collards: "Tastes like a cross between cabbage and kale." Collards are a rich green colour.
Chard: A beet relative also known as Swiss chard, it has characteristic "crinkly green leaves and silvery, celery-like stalks." The agriculture experts at Colorado State say it has "a mild, sweet earthy taste with some bitterness." Varieties include rhubarb (dark green leaves with red stalks, not to be confused with the rhubarb often used in baking), ruby (red stalk and red veins) and rainbow, which covers all kinds of colours mixed together.
Mustard: These leaves of the mustard plant "are a rich, dark green and have a pungent mustard flavour."
Buying and storing
In general, look for greens that are dark in colour with crisp leaves. Avoid anything cracked, yellowed, limp or browning.
Try to find collards without prominent white veins or cracks, which indicate the leaves are overmature, Harold McGee says in "Keys to Good Cooking." Getting those tougher bits to cook through means you may end up overcooking the rest of the leaf. As far as kale goes, "Food Lover's Companion" suggests looking for small bunches with rich colours.
Store greens in a cold part of the fridge, inside a plastic bag in the more humid crisper drawer, if you can, for a few days, or up to a week, depending on the type.
Cleaning and prep
Greens have been associated with a number of outbreaks of foodborne illness, so don't skip cleaning them. Because greens (chard, bok choy, spinach, collards, kale, etc.) tend to grow in sandy soil, you should take care to get all the gritty deposit off them, writes Deborah Madison in "The New Vegetarian Cooking for Everyone." Her process: Trim, rinse under tap water and swish in a large basin of cold water. Give them a few minutes in there, if they're especially dirty. Then just lift the greens out and let the debris stay on the bottom. Repeating the soak as necessary and dry with a salad spinner or towels.
Kale stems are too tough to eat. The best advice I've heard on getting the leaves off the stems came from television personality and cookbook author Rachael Ray. Curl your fingers like a cat about to pounce - stick with me - and strip the leaves off the stems in one smooth motion. It works, I swear.
Or not cooking, as the case may be: Kale is especially good raw in salads. To make those leaves nice and tender, give them a good massage. Bon Appétit suggests doing this with salt and some lemon juice or vinegar (you can also use some oil) and gently rubbing the leaves in your hands just until they start to soften. You want them to retain some crispness, though. Don't bother doing this if you're adding a dressing and letting the salad hang out for a bit.
Wilting is not the kind of thing you want to be described as doing on a hot summer day, but for greens, it can be a good thing. As McGee says, you can reduce the volume of leafy greens by half when you heat them briefly in a hot, oiled pan. No need to worry about adding too much to the pan, as they quickly cook down, he says. If you really have a lot, add them in batches. You can flavour your wilted greens by sauteing some aromatics (garlic, onion, spices) in the pan first. Use them as a topping on toast or pasta, or incorporate them into a frittata. They're also great as a side on their own.
To reduce bitterness, McGee recommends boiling the greens in plenty of water and then adding salt or salty ingredients, such as soy sauce or anchovy paste, because salt covers up our perception of bitter flavours.
If you cook collards, mustard greens or kale too long, McGee notes, you can get a strong sulfurous aroma. Smoked ham in long-cooked collards recipes can balance things out. To keep the cook time short for collards and kale, McGee suggests removing the tough stalks and veins or shredding the whole leaves. (He recommends boiling mustard greens.) Another option is to cook the whole leaves just until the green part is tender and the stalks still crisp, and then cutting the leaves crosswise into thin shreds.
Some greens can also benefit from cooking the stems and leaves separately. I've successfully done this with chard, wilting the leaves and sauteing the stems. Coloured chard is especially prone to leaking colours, so McGee recommends combining it with your other ingredients at the last minute, if possible.