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David Trinklein
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Plant Science & Technology
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2022: Year of the Salad Greens

March 17, 2022

minute read

The term "salad greens" does not excite the taste buds of most people the way fresh sweet corn and vine-ripened tomatoes do. This is understandable. However, research has shown that those who regularly include salads in their diet have higher blood levels of powerful antioxidants such as vitamin C and E, folic acid, lycopene, and alpha- and beta-carotene. Additionally, salad greens are low in calories but high in dietary fiber. Is it any wonder, then, that the National Garden Bureau has declared 2022 as "The Year of the Salad Greens?"

Although their names are sometimes unfamiliar and their tastes exotic, leafy greens are popular at gourmet restaurants, farmers' markets, supermarket produce sections and backyard gardens. The extensive variety of greens available today offers textures from crisp to creamy, flavors from sweet to pungent, and colors in beautiful shades of green and red.

plate of salad

Greens have been consumed by humans for millennia. There is evidence that Asian greens such as the mustards and mizuna have been cultivated for more than 2500 years. Lettuce has been enjoyed since 550 BC when it was first served to Persian kings. These early types of lettuce were probably collected from the wild and looked different than the varieties eaten today. The Assyrians and Egyptians ate lettuce and thought that the milky sap found in lettuce plants was an aphrodisiac. Paintings of a lettuce with long pointed leaves similar to today's romaine varieties have been found in Egyptian tombs.

The Romans were especially fond of a type of lettuce with erect leaves that had been found growing on the island of Cos in Greece. Today it is known as romaine, named after the place where it was popular, or Cos, for its place of origin. It has been grown for thousands of years and may be the oldest lettuce variety still cultivated today. The Romans also liked arugula and ate it for good luck.

Corn salad, also called mache, was originally found in Europe growing in the fields of grain, commonly referred to as cornfields. Peasants working in the fields would collect the leaves to eat. It became popular when served to the elite during the reign of Louis XIV.

In the U.S. greens have been served on dinner tables since the early settlers arrived from Europe. General George Washington recommended that his soldiers eat them as "they are very conducive to health, and tend to prevent the scurvy." A member of Washington's troops was sent out every day to gather the greens growing around their camp and distributed them among the soldiers. President Thomas Jefferson, an avid horticulturist, grew a variety of greens at Monticello, including a selection of lettuces, along with endive, cress, spinach, corn salad and others.

Micro-greens (credit Francesco Di Gioia; Penn State University)

Greens are a diverse group of plants that are grown primarily for their edible leaves. Greens can be harvested at many different stages of growth. As a "micro-green," plants are harvested as young seedlings with only one or two true leaves, usually within 10 to 14 days of seeding. They are delicious in salads and sandwiches, and often used as an edible garnish. Plants allowed to grow a couple more weeks can be harvested for use as "baby greens." Small but full of flavor, the tender, bite-sized leaves are an essential element of gourmet menus. Of course, greens also can be allowed to grow to full size before being harvested.

Many of the greens grown today are members of the Brassicaceae (cabbage) plant family. This family of economically important plants includes broccoli, cabbage and cauliflower and gives us a wide variety of greens including arugula, mizuna, tatsoi, cress, collards and mustard greens. Most greens are annuals, though sorrel and cress are perennials that can be grown as annuals.

Arugula

Arugula (Eruca sativa) also called roquette, rocket salad or rocket, is easy to grow with green leaves that are lobed and add a spicy snap to salads. A popular green in Europe, it is used in many Italian and French dishes. When young, the leaves have a mild, radish-type tang that is sometimes compared to the flavor of horseradish. Many people like to combine arugula with other milder greens to balance the stronger flavor.

Tatsoi (credit: Emily Rader)

Asian greens such as mizuna (Brassica rapa japonica) and tatsoi (Brassica rapa rosularis) are becoming popular in American gourmet cuisine. Mizuna has white stems and delicate green leaves with finely cut fringed edges. It is tolerant of most weather and grows in hot temperatures without bolting. Tatsoi, also called spoon cabbage or rosette pak choi, has very dark green leaves, appearing almost black in color, with a mild peppery flavor. Tatsoi is very weather tolerant and continues to grow through cold temperatures and light snow. It also tolerates heat so several plantings can be made from spring through fall. Tatsoi is prized as a baby green and grows quickly into mature plants.

Garden Cress

Cress, also called garden cress or pepper grass (Lepidium sativum) is a fast-growing green harvested as a sprout within a week or so after germination. It has a tangy, pepper-like flavor and aroma. 'Wrinkled Crinkled Crumpled' cress is aptly named. It is a fast growing, large leafed cress with extremely curly leaves that takes a little longer to mature. Garden cress is different from watercress (Nasturtium officinale), a perennial that grows in running water or very damp areas. Land cress (Barbarea verna) is a related perennial cress that is known by many different names including American cress, early wintercress, early yellowrocket, and in the South, creasy greens. Unlike garden cress, it is eaten about 7 weeks after sowing when plants have developed 6-inch diameter rosettes of glossy, dark green leaves. It is similar to watercress but is easier to grow in the garden.

Collards

Collards (Brassica oleracea, Acephala group) are a type of non-heading cabbage with large, blue-green, coarse leaves with a distinct cabbage-like flavor. Each plant produces many leaves and can be harvested as micro-greens, baby greens, or when fully mature. Collards grow well in the heat, yet they're very cold tolerant. Exposure to frosts sweetens the flavor of the leaves.

Mustard greens

Mustard greens (Brassica juncea) is a cool-season vegetable that produces large leaves that get a foot or more tall. It can withstand some frost but may bolt when day lengths get longer in the spring. Harvesting the outer leaves from mustards can begin when they are only 3 to 4 inches tall. 'Southern Giant Curled' is a longtime favorite. Slow to bolt, it produces upright, bright green leaves with curly edges. If color is what you want, consider 'Red Giant.' True to its name, the large leaves are up to 18 inches tall with a beautiful reddish bronze color and reddish- purple veins. The leaves have the tangy flavor of gourmet mustard. 'Ruby Streaks' is another colorful mustard that is stunning and quite tasty.

The various types of lettuce (Lactuca sativa) are popular salad greens that belong to the Asteraceae (daisy) plant family and are the foundation of many vegetable gardens. Easy to grow and quick to harvest, there are hundreds of varieties available to gardeners. The leafy or non-heading types of lettuce are most often used as greens. This includes varieties of bibb, romaine, and leaf lettuces.

'Buttercrunch' bibb lettuce

Butterhead or Boston lettuce forms a semi-firm head. The leaves are less crisp than bibbs and have a wonderful buttery texture. They reach full size about 8 to 10 weeks after planting. 'Buttercrunch' is a long-time favorite whose compact heads produce delicious, green leaves that can be harvested when small and served as an individual-sized salad. Even smaller is 'Tom Thumb,' a crisp and sweet butterhead about the size of a tennis ball. This is an ideal variety for growing in containers or for gardeners with very limited space.

Coss (Romaine) lettuce

Coss or romaine lettuce has large green wrinkled leaves with a nice crisp texture and flavor. The oblong leaves grow upright and form loose, cone-shaped heads. It is the essential ingredient for a traditional Caesar salad. Romaine lettuce takes a little longer to reach full size than other types of lettuces, generally 9 to 10 weeks after planting, but they are also more heat tolerant. 'Parris Island Cos' is a standard romaine with crinkled, medium green leaves that form a large tight head. It resists tip burn and is slow to bolt. 'Rouge d'Hiver' (Red Winter) is another variety popular for the nicely sized heads of reddish-bronze leaves that stay crisp after harvest. It is very tolerant of both hot and cold temperatures making it ideal for any garden.

'Red Sails' leaf lettuce

Leaf lettuce provides a quick harvest and comes in a variety of colors, shapes and textures. Seed racks and catalogs are filled with so many varieties it may be hard to choose which one to grow. Fortunately, a lot of lettuce can be produced from a small row or even in a container so there's probably room to plant more than one variety. Or choose one of the many custom lettuce blends created by seed companies. These mixes are a great way to sample many different lettuces from a single packet.

Leaf lettuce is very easy to grow and produces abundantly until hot temperatures arrive. Leaves come in shades of green and red ranging from light lime green to deep wine red. They can be harvested at almost any size but most reach full size 40 to 50 days after planting. Leaf lettuces are also popular as cut-and-come-again lettuces. When the leaves are mature, harvest the whole plant, just make sure to cut above the growing point so that the plant will grow back to provide a second harvest of tasty leaves.

Although introduced to the public over 150 years ago, 'Black Seeded Simpson' continues to be one of the most popular leaf lettuce varieties. It is prized for its large, light green crinkled leaves and its tolerance of drought, heat and frost. Slow to bolt, its leaves can be picked over a long harvest period. 'Oakleaf' is another long-time favorite that derives name for having very tender leaves that resemble those of the white oak. It, too, is slow to bolt. To add color to salads, 'Red Sails' has soft, buttery leaves ruffled and edged with burgundy. The darkest of lettuces, 'Merlot' forms loose heads of intense red leaves that appear almost purple in color.

Additional salad greens from other plant families include:

Smooth-leafed spinach

Spinach (Spinacia oleracea) belongs to the Amaranthaceae (amaranth) plant family, sub-family Chenopodioideae. A hardy cool weather crop, spinach can be used as a salad green or cooked as a green vegetable. There are two main types of spinach: smooth leaf and savoy (crinkled leaf). Both grow equally well and are "powerhouses" of human nutrition. 'Bloomsdale Long Standing' is a tried and proven variety that is slow to bolt when the weather warms. Spinach contains calcium oxalate crystals which can cause gastric distress for people with sensitive stomachs. Cooking largely removes the calcium oxalate and makes the vegetable palatable for all.

Mache or corn salad

Mache or corn salad (Valerianella locusta) is also called lamb's lettuce. Mache is from the Valerianaceae (honeysuckle) plant family, which includes the garden perennials Jupiter's beard and valerian. Mache's glossy, spoon-shaped leaves are mild with a sweet nutty flavor and grow in attractive small rosettes. 'Vit' is a popular variety that can be grown in both spring and fall, and produces a dense mound of firm, leaves with tender flavor. With good cold tolerance, it is also ideal for overwintering when grown in milder climates.

Red-veined garden sorrel

Garden Sorrel (Rumex acetosa), sometimes called spinach dock, is a member of the Polygonaceae (buckwheat) plant family. It is a hardy perennial in USDA zones 4 to 9, but often grown as an annual. As a perennial, it is one of the earliest greens to harvest in the spring. It continues to produce into fall and often early winter, withstanding temperatures well below freezing. The long green spoon-shaped leaves have a sharp, mildly sour, lemony flavor. 'Red Veined Sorrel' has contrasting dark red stems and veins for added color.

Whatever the species, greens are generally started from seed and are readily available in packets from retail stores, catalogs and Internet seed companies. Economical and easy to start from seed, they are available as individual varieties and in pre-made seed mixes in a range of flavors, colors and uses to suit any gardener or cook.

Greens grow best in a fertile, well-drained soil. Add compost or well-rotted manure to the soil before planting to improve drainage and add nutrients. Scatter seeds in a row and cover lightly with soil. In the case of lettuce, light is needed for germination to occur. Keep soil moist until seeds germinate, usually within 7 to 14 days. After seeds germinate and start growing, start to thin crowded seedlings. The best way to remove excess plants without damaging the other seedlings is to pinch them at the base of the stem with your fingernails or snip them off with a sharp scissors. But don't throw these seedlings away. The small seedlings are delicious in salads and sandwiches as micro-greens.

Most greens like to grow in full sun, but they will produce in areas with light shade. Sow seeds outdoors in spring or fall. For an extended harvest, make smaller plantings every two weeks. As summer approaches, plant varieties of greens that are heat tolerant or resist bolting. Additional plantings of greens can be made in late summer or fall (up to a month before the first frost) for harvest during the cooler temperatures. Greens can also be grown in an unheated greenhouse, under row covers and in cold frames to extend the growing season.

Leaf lettuce in raised bed

Greens are ideal for growing in pots and containers. Choose a well-drained container that's at least 4 to 6 inches deep and fill with a soilless media available at retail stores. Check the soil daily to make sure it hasn't dried out and water as needed. When growing micro-greens, seeds can be planted in shallow flats and harvested about 10 to 21 days after planting. If adequate light is available, they can also be grown indoors during the winter.

The salad greens are relatively free of pests and diseases because they grow quickly, often in cooler weather when fewer insect pests are present. However, it's a good idea to check plants regularly to prevent a minor problem from turning into a major one.

As previously mentioned, salad greens can be harvested at almost any stage of growth. For micro-greens, harvest seedlings when they have one or two true leaves, usually 10 to 21 days after being planted. For baby greens, pick leaves after 3 or 4 weeks of growth. Later, entire plants can be harvested or leaves removed at the base of the plant starting with the outer leaves. Inner leaves will continue to grow and new leaves will be produced from the center.

Adequate spacing is most important when growing plants to full size. This is easy to accomplish by simply thinning plants as they begin to get crowded in the garden. Mature greens need about 8 to 10 inches between plants. When plants reach full size, harvest the entire plant by pulling the plant out of the ground or cutting it off at the soil line with a knife or sharp scissors. Plants that have reached the end of their growing cycle will send out a flower stalk, in a process called bolting. Many greens also will bolt when temperatures get too high. When this happens, leaves become bitter tasting and inedible; therefore, remove plants that are bolting from the garden.

Greens are best eaten fresh from the garden but can be stored in a vegetable crisper in a refrigerator for a day or two. Lettuce, collards and mustard greens can be kept up to a week. Before storing, remove any remaining soil and damaged or discolored leaves that you won't be eating. Place in a plastic bag. Rinse greens thoroughly with cold water just before using.

Whether it's the enjoyment of growing healthy plants or the pleasure of nutritious food, gardeners and cooks alike appreciate the versatility of salad greens. The "Year of the Salad Greens" is a good time to fill your garden and your kitchen with the inspirational colors, flavors and textures of leafy greens.

Credit: Adapted from an article by the National Garden Bureau (https://ngb.org).


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REVISED: March 17, 2022