Leafy Greens

History

Collards and kale are both members of the Brassicaceae family, also known as the cabbage family, which includes other cool-season cole crops like cabbage, broccoli, Brussels sprouts, cauliflower, and radish (see Figure 1). However, collards and kale are distinct from much of the cabbage family since they do not form heads; instead, their leaves are harvested.

The Latin name for the variety of collards and kale, acephala, actually means “without a head” and can be considered “primitive” or “original” cabbages that have been produced for thousands of years. These leafy greens are thought to be native to the eastern Mediterranean and Asia Minor, and have been recorded as produced by the early Greeks and Romans, who likely introduced them into Western Europe around 400 B.C. Kale was first mentioned in 200 B.C. In 1669, kale and collards were recorded in the U.S. Today, collards are very common in the South as a cool season crop. See Figure 3.

Spinach and Swiss chard are both members of the Chenopodiaceae family, also known as the beet or Goosefoot family, which also includes beets, quinoa, and lambsquarters (see Figure 2).

Spinach is thought to have originated in the Middle East (likely Iran). It was brought to Spain between 800-1200 A.D. by the Moors and into Europe in the 15^th century. Around 1806, spinach was introduced to the U.S. It became very popular in the early 1900s, in part due to the comic strip character Popeye. Swiss chard originated in Sicily, Italy and remains popular in the Mediterranean and across Europe. After the American Civil War, Swiss chard became more popular in the U.S. See Figure 3.

These leafy greens — collards, kale, spinach, and Swiss chard — are actually biennials (the plant’s life cycle from seed to flower takes two years) but are most commonly grown as an annual crop (one season/year).

Varieties

Collards and kale are heat and cold tolerant, very productive, and easy to grow leafy greens (see Figure 4). The plant’s leaves are harvested and, in cooler seasons, are particularly sweet and tender. Collards and kale are similar leafy greens, differing mainly in leaf appearance and taste. Both can be grown almost year-round. Collard varieties do not differ widely in appearance or taste, while kale varieties show more diversity in leaf color, shape, texture, and length. Kale can also be harvested as either baby leaf (ideal for salads) or full size.

Spinach is a fast-growing cool season leafy green that produces the sweetest and largest leaves during cool months and short days (see Figure 4). Varieties of spinach are fairly similar in appearance but vary in the texture of the leaves (savoyed/curled leaf or smooth).

Swiss chard is also a cool season crop and though it can usually withstand a light frost, it is not as cold hardy as the other leafy greens (see Figure 4). Swiss chard is more heat tolerant than the others and usually remains productive throughout the summer, making it a great alternative green to lettuce during the warm season. The leaves and stems are edible, and Swiss chard varieties have stunningly colored stems. “Rainbow” chard (or Bright Lights variety) is very popular due to its array of colors (gold, pink, orange, purple, red, white).

Leafy greens have either open-pollinated (including heirloom) or hybrid varieties. Some leafy greens are heirloom varieties, like Georgia collards and Lacinato kale, meaning the seeds have been saved for at least 50 years, can be saved each season and replanted, and are open-pollinated.

Flowers produced by these leafy green crops are perfect (both male and female flower parts) but are prone to cross-pollination. If saving seed, different varieties should be separated by a distance of 800 feet-1/2 mile between different varieties to avoid cross-pollination. Generally, it is not recommended to save seed for future planting with hybrid varieties as they are usually not expressed properly in the next generation.

See the recommended leafy green varieties (collards, kale, spinach, and Swiss chard) for Louisiana in Table 1.

Table 1. Recommended Leafy Green Varieties for Louisiana

When and How to Plant

For all leafy greens, refer to the Leafy Green Planting Guide (Table 2) for recommended planting dates and spacing for full-sized plants; if planting for baby leaf, these recommendations can be decreased due to the smaller size.

Collards and Kale

For spring season extension, start seeds inside approximately 4 weeks before the recommended planting dates (see Table 2). Using seed germination trays (with at least 1.5-inch diameter cells), plant 1 seed per cell (unless germination rate is low or conditions are less than ideal; then plant 2 seeds per cell) at a shallow depth (1/8-1/4 inch), just deep enough to be covered with a thin layer of soilless potting mix. Make sure to keep the seed trays in a warm, well-lit area (optimum germination temperature is 85 degrees F), and keep the soil moist, which usually requires daily light watering. A seedling heat mat and plastic dome lid are helpful in maintaining ideal germination conditions. If multiple seeds were planted per cell, thin seedlings to one plant per cell after a few true leaves develop. Collards and kale are generally very transplant hardy. If the soil can be worked, seedlings can be transplanted outside approximately 2 weeks later or when 4-6 true leaves develop. A few days before transplanting outside, it is recommended to follow a hardening-off process to transition seedlings to outdoor conditions.

If direct seeding outside for spring planting, soil temperatures must be above 45 degrees F and under 95 degrees F for seed germination. The use of a soil temperature map can help guide planting decisions. It is recommended to direct seed at a shallow depth of 1/8 inch in rows. When direct seeding outside, either follow the recommended plant spacing (refer to the Leafy Green Planting Guide, Table 2) or scatter seeds (broadcast) in a 2-inch-wide furrow or line that is about 1/2-inch deep. Lightly cover with soil and water in. Thin to the recommended plant spacing after true leaves develop.

Leafy greens will produce more flavorful greens in the cool season, especially after a light frost. Both collards and kale prefer average growing temperatures between 60-65 degrees F but are tolerant to heat and cold. For a continuous supply of baby leaf kale, plant seeds every 4-5 weeks.

Spinach

This crop is usually direct seeded outside at a shallow 1/4-inch depth in rows. When direct seeding outside, you may follow the recommended plant spacing (refer to Leafy Green Planting Guide, Table 2) or scatter seeds (broadcast) in a 2-inch-wide furrow or line that is about 1/2-inch deep. Lightly cover with soil and water in. Thin to the recommended plant spacing after true leaves develop. Spinach may be started inside and then transplanted outside after the last frost but may need extra care to survive. As a cool season leafy green, the optimal soil temperature range for germination is 45-75 degrees F with an optimum of 70 degrees F. Spinach seeds should not be sown if the soil temperature is over 85 degrees F, as higher temperatures reduce germination success. The use of a soil temperature map can help guide planting decisions.

Spinach can be an early spring, late fall or winter crop, and may even survive winter temperatures. The optimum growing temperature for best growth and quality is 60-65 degrees F, at 40 degrees F minimum and 75 degrees F maximum. However, spinach is frost tolerant, and well-established plants are cold hardy to 20 degrees F. Longer days trigger bolting. For a continuous supply of spinach, plant every 2 weeks, or every week for baby spinach.

Swiss Chard

To extend the growing season, it is recommended to start seeds inside about 5-6 weeks before transplanting outside. Using seed germination trays (with at least 1.5-inch diameter cells), plant 1 seed per cell (unless germination rate is low or conditions are less than ideal; then plant 2 seeds per cell) at a shallow depth (1/8-1/4 inch), just deep enough to be covered with a thin layer of soilless potting mix. Make sure to keep the seed trays in a warm, well-lit area. Keep the soil moist, which usually requires daily light watering. Seeds will germinate in soil temperatures between 50-85 degrees F, but most rapidly around 85 degrees F (maximum temperature of 95 degrees F; minimum of 40 degrees F). A seedling heat mat and plastic dome lid are helpful in maintaining ideal germination conditions. If multiple seeds were planted per cell, thin seedlings to one plant per cell once a few true leaves develop. Swiss chard is generally very transplant hardy, and seedlings can be transplanted outside approximately 2 weeks later. A few days before planting transplants outside, it is recommended to follow a hardening-off process to transition seedlings to outdoor conditions.

If direct seeding outside sow seed at a depth of 1/4 inch, cover with soil or compost, and lightly water. Soil temperature should be between 50-85 degrees F. A soil temperature map can help guide planting decisions. When direct seeding outside, you may follow the recommended plant spacing (refer to Leafy Green Planting Guide, Table 2) or scatter seeds (broadcast) in a 2-inch-wide furrow or line that is about 1/2-inch deep. Lightly cover with soil and water in. Thin to the recommended plant spacing after true leaves develop.

Swiss chard is very heat tolerant and may survive a light frost. For a continuous supply of baby leaf chard, plant seeds every week.

Table 2. LEAFY GREEN PLANTING GUIDE

Where to Plant

Plant these leafy greens in deep, well-drained, fertilized soil with a pH of 5.5 to 7.5. Spinach is less tolerant of acidic soil, so soil pH should be above 6.0. Leafy greens prefer full sun (6 hours/day), although they may tolerate partial shade. They are also tolerant of sandy or heavy soil if there is good drainage, and planting into raised beds will aid in good drainage. It is recommended to plant leafy greens in box beds or traditional raised garden rows that are about 12 inches tall to ensure good drainage (and allow for the spinach taproot). In all types of gardens, it is recommended to add a layer of compost, peat moss, rotted hay, or other organic matter and mix into the soil to optimize plant health. If mature leaves are small and pale, increase plant spacing to reduce crowding or apply fertilizer. Yellowed spinach leaves may indicate a magnesium deficiency.

Reflective plastic mulch — or a plastic fabric/film — is recommended to deter aphids that transmit viruses, to increase soil temperature, and to control weeds. Drip irrigation is also recommended when using plastic mulch to maintain ideal soil moisture and to encourage productive plants.

Each season, rotate plant families — avoid planting crops from the same plant family in the same area of the garden — to reduce disease and pests. It is recommended to rotate the Brassicaceae crops (collards and kale) on a longer, 4-year cycle.

Plant Care

Watering

Thoroughly water plants weekly; a general recommendation is 1 inch of water per week. More frequent watering is needed during warm weather and on sandy soils. Deep roots are encouraged by soaking the plants.

Fertilization

Nitrogen may be in short supply early in the cool growing season that is ideal for leafy greens. Leaves may appear yellow or light green. Additions of organic matter to planting beds can increase microbiological activity in cold soils and therefore aid in uptake of nutrients. A water-soluble fertilizer solution may be used on young plants if deficiency symptoms are observed. Seaweed extracts, fish emulsion, diluted compost tea or a synthetic water-soluble fertilizer may be used.

Organic fertilizers such as compost, fish emulsion, composted poultry litter or manure, worm castings, and blood or bone meal originate from living organisms. They are far more environmentally sustainable and safe than traditional synthetic fertilizers. They naturally release nutrients more slowly and over a longer period of time. When applying organic fertilizer, it is important to use in unison with compost, cover crops, and crop rotation, which all work together to build soil health. Learn how to convert inorganic fertilizer recommendations to organic fertilizers here.

Alternatively, a synthetic fertilizer may be used at a rate of about 1.5 lbs (3 cups) of 13-13-13 for every 25 feet of row or 75 square feet. Broadcast, or sprinkle evenly, over the soil and then mix in about 3-6 inches deep using a rake. Supplemental sidedressing, or reapplication of synthetic fertilizer, is recommended 3-4 weeks after transplanting. Sidedressing is the addition of a small amount of fertilizer to the soil around already established plants when the plant begins to fruit or vine, primarily to provide nitrogen. When using synthetic fertilizer, sprinkle lightly around each plant, keeping it about 6 inches away from the plant stem; water into the soil. Additional sidedressing may be applied every 3-4 weeks. Because of their slow, steady release of nitrogen, crops fertilized with organic fertilizer do not usually need to be sidedressed, but fish emulsion may be used for a quick-release source of nitrogen if leaves show yellowing.

Weeds

Plastic mulch will control most of the weeds; hand-pull weeds close to the plant, especially in the planting holes. It is especially important to control weeds around spinach plants since the shallow roots compete directly with weeds.

Insect Pests and Diseases

Collards and kale are susceptible to cabbage worms, harlequin bugs, and black rot. For spinach, blight and seed or root rot are also possible, with higher risk in cool and damp weather. Swiss chard may experience leaf spots, pocket rot, and damping off. Most leafy greens are susceptible to aphids, leaf hoppers, leaf miners, flea beetles, Fusarium wilt, and downy mildew. It is recommended to cover seedlings with row cover at the time of planting to prevent insect pest pressure. Some of these leafy green insect pests and diseases are described in more detail in Table 3, but common prevention and management methods include removal of plant debris, crop rotation, and increased air circulation.

Table 3. Organic and Natural Management for Common Leafy Green Insect Pests and Diseases

Harvest and Storage

Collards and Kale

The most common method is to harvest lower leaves first by breaking off with your hands or clipping close to the stem. Another option is to cut the entire plant about 4 inches above the soil, though the plant may not grow back. Most varieties are very frost tolerant and fall plantings may produce all winter.

Spinach

Like other leafy greens, spinach may be harvested as a whole plant or by removing outer leaves. Begin harvesting once the plant has about 6-8 leaves that are 3-4 inches long. For bunching spinach, clip just below the root to harvest the whole plant. When harvesting loose leaves, clip or pinch off outer leaves or those closest to the soil first, since these will be the most mature. Since spinach grows so close to the soil, leaves should be thoroughly washed.

Swiss Chard

The full-sized leaves, with stems intact, should be harvested at the base of the plant using shears. Leaves are mature at 8-10 inches long. If harvesting baby leaf chard, leaves are ready when they reach about 3 inches long and should be harvested at the base of the plant using shears or by hand.

Here are some helpful harvesting videos:

1. How to harvest kale leaves (same method for collards and Swiss chard)
2. How to harvest spinach leaves

For all leafy greens, never remove more than a third of the leaves at one harvest (unless harvesting the entire plant) to allow for regrowth. It is recommended to remove yellowed or damaged leaves from the plant to increase productivity. Continuous harvesting will encourage productive plants and new leaf growth. Harvested leafy greens should be cooled immediately to prevent wilting. At an ideal storage temperature of 32 degrees F with high humidity (95-100%), the crop will last approximately 10-14 days for collards and spinach, and 2-3 weeks for kale. Cut stems can be stored in a jar of water, just as you would store cut flowers, inside the refrigerator. Store loose leaves (spinach and baby leaf varieties) in a plastic bag.

Leafy greens can be preserved by freezing after washing, blanching, and draining.

Leafy Greens are Nutritious and Good for You

Very high in Vitamin A

Important for eye health, a strong immune system, and cell growth

High in Potassium

Essential for body function, especially the heart, kidney, nerves, bones, and muscles

Rich in Vitamin C, E, and B6

Important for bones, skin, blood vessels; repairs damaged cells; supports immune system and brain health

Provides calcium, iron, and magnesium

Bone health; produces red blood cells; important in muscle and nerve function

Good source of dietary fiber

Important for bowel health, lowering cholesterol, controlling blood sugar, and maintaining a healthy weight

Recipes

Common methods of preparing and cooking collards, Swiss chard, kale and spinach

Taste-testing ideas: green smoothies, mini quiches with leafy greens, spinach salad, kale chips, greens and cheese quesadilla, pasta with rainbow chard

Other websites with many leafy green recipes:

USDA MyPlate Kitchen: Kale, Spinach

SNAP-Ed: Collards, Kale, Spinach

Produce for Better Health Foundation: Spinach, Kale

Tufts Sustainable Farming Project: Swiss chard

Sources

• Southeastern Vegetable Extension Workers, 2020 Southeastern U.S. Vegetable Crop Handbook
• LSU AgCenter, Louisiana Vegetable Planting Guide
• LSU AgCenter, Louisiana Commercial Vegetable Production Recommendations
• UF Extension Planting Guide
• Vegetable Production Handbook of Florida
• Texas A&M AgriLife Extension, Vegetable Varieties for Central Texas
• Texas A&M AgriLife Extension, Easy Gardening: Collard Greens
• Texas A&M AgriLife Extension, Commercial Crop Guides: Collards/Kale
• Texas A&M AgriLife Extension, Aggie Horticulture: Greeks and Romans grew kale and collards
• Texas A&M AgriLife Extension, Aggie Horticulture: Greeks and Romans grew kale and collards
• Texas A&M AgriLife Extension, Easy Gardening: Spinach and Other Greens
• Alabama A&M & Auburn Universities Extension, Crop Production,
• UMass Extension Vegetable Program: Disease, Insect, and Mites Fact
• USDA SNAP-Ed Connection: Spinach
• USDA SNAP-Ed Connection: Swiss Chard
• USDA SNAP-Ed Connection: Kale
• USDA SNAP-Ed Connection: Collard Greens
• Purdue Extension FoodLink: Kale
• Purdue Extension FoodLink: Collard Greens
• Purdue Extension FoodLink: Chard
• Purdue Extension FoodLink: Spinach
• University of Arizona CALS: Spinach
• Colorado State Food Source Information: Swiss Chard
• Maynard, Donald N & Hochmuth, George J (2007). Knott’s Handbook for Vegetable Growers (5th edition). John Wiley & Sons, Inc.
• Decoteau, Dennis R (2000). Vegetable Crops. Prentice-Hall, Inc.
• Swiader, John M & Ware, George W (2002). Producing Vegetable Crops (5th edition). Interstate Publishers, Inc.
• Sukprakarn, S, Juntakool, S, Huang, R, and Kalb, T (2005). Saving your own vegetable seeds—a guide for farmers. AVRDC publication number 05-647. AVRDC—The World Vegetable Center, Shanhua, Taiwan. 25 pp.
• Seed Savers Exchange, Seed Saving: A Guide to Isolation Distances
• University of Georgia Extension, How to Convert an Inorganic Fertilizer Recommendation to an Organic One, Circular 853