Leafy greens like lettuce, spinach, kale, collards, mustard, endive, and chard are great cool-season vegetable crops. They are some of the easiest vegetables to grow making them perfect for beginners.
Leafy greens are best grown in the cool spring and fall growing seasons. They tolerate cool temperatures and can even survive light frost and most leafy greens
have shorter production times than many other vegetables. This makes them the perfect crop to start early in the spring. You can get an entire crop of leafy greens grown and harvested in spring before you plant many warm-season vegetables, like tomatoes or squash. Once warm-season vegetables are harvested in the fall, you can typically grow another round of leafy greens in the cool fall months before winter arrives. While some leafy greens, like chard, will tolerate warm summer temperatures, most do not grow well in the heat of summer often dying out or bolting (flowering) when temperatures get hot.
In Iowa, plant leafy greens in early April. Leaf lettuce and spinach can typically be harvested 4 to 6 weeks after seeding. Stagger plantings by one week to provide a steady supply of greens over a longer period. Other leafy greens like kale, collards, mustard, endive, and chard will be ready to harvest 8 to 10 weeks after planting in early April. These leafy greens are more heat tolerant and some may grow through the hot summer months, especially if provided enough moisture. A second crop of leafy greens can be planted in mid to late August for harvest in October and November.
Leafy greens need moist well-drained soils and full sun. Greens, especially leaf lettuce and spinach, can tolerate more shade than most vegetables. Plants are still productive even in locations that are too shady for growing other vegetables. Provide at least six hours of direct sunlight a day for best growth.
Most leafy greens do well in containers. Their smaller size and short production time make them perfect vegetables to grow on a patio or deck. Any container six to eight inches in diameter or larger can be used. The larger the container the better and window boxes work particularly well for greens like leaf lettuce and spinach. Utilize regular potting soil and provide full sun and adequate moisture.
Leafy green vegetables can be directly sown into the garden. In spring, they can be planted as soon as the soil can be worked. Take care to not work in soil that is too wet. The soil should crumble apart when a handful is squeezed. If the soil sticks to tools and shoes and forms a muddy ball when you squeeze it, conditions are too wet. Seeds are often small and must be planted at the proper depth. Some species, such as lettuce, require light for germination and are only covered by ¼ inch or soil to ensure good soil contact but not block out light. Consult the seed package to ensure the proper planting depth.
Sow seed in wide, banded rows 12 to 24 inches apart to make more efficient use of garden space. Once seedlings emerge thin plants to provide 3 to 6 inches between plants. Kale, collards, and endive benefit from 15- to 18-inch spacing. Thinning helps improve yields by reducing competition for light, water, and nutrients.
Greens can also be started indoors and transplanted into the garden in early spring to help get a crop even earlier. This is particularly beneficial to allow leafy greens to mature before the hot temperatures of summer arrive. Start seedling two to three weeks before the anticipated transplant date and plant outdoors in early April after hardening plants off for 5 to 7 days.
Growing and Care
Leafy greens require cool, moist growing conditions. Daytime temperatures of 70 to 75°F and nighttime temperatures of 55 to 60°F are ideal. Adequate supplies of moisture and nutrients are also important. Leafy greens require one inch of water per week, provided by the gardener when not supplied by Mother Nature. A complete fertilizer, such as 10-10-10, applied to the garden at a rate of 2 to 3 lbs per 100 square feet prior to planting should be adequate for successful growth. Leafy greens tend to have shallow root systems. Cultivate lightly to remove weeds without disturbing the roots. An organic mulch like grass clippings, clean straw, or coco mulch can also help reduce weeds as well as conserve soil moisture, and moderate soil temperatures.
Bolting is a common problem experienced by gardeners, especially in lettuce. Bolting is the undesirable formation of flowers and seeds. Bolting destroys the flavor of the leaves by making them bitter and tough. It is caused by high temperatures, long periods of high light intensities, and drought. Bolting is common in the early summer as days get longer and warmer. The exact timing of bolting varies from species to species and cultivar to cultivar. Keeping conditions cool and reducing light intensity as days get longer will help delay bolting. Once the flower stalk forms, it's best to remove plants and start a new crop when temperatures are cooler and the day lengths are shorter.
Potential Pests and Diseases
Most leafy greens are relatively disease and insect pest free. Occasionally aphids, leafminers, leafhoppers, slugs, and caterpillars like cabbage looper, cabbageworm, armyworm, and cutworms can be problems. More rarely diseases like downy mildew can develop. Plants growing in ideal conditions with adequate sunlight, moisture, and air circulation can typically out pace pest insects. For home gardeners, aphids are the most common pest on leafy greens. Selective pruning and dislodging with a stream of water can help reduce aphid populations. Biological controls or an insecticide, like horticultural soap or neem oil, can be used. Always follow the label directions when using pesticides.
Harvesting and Storage
Once leaves are large enough, they can be harvested. Leaf lettuce and spinach are typically harvested when leaves are 4 to 6 inches long. Kale, collards, mustards, and chard can be harvested when leaves are about 10 inches long. Simply remove leaves with sharp scissors or pruners. The entire plant can be harvested when the leaves are fully developed. This is the typical method of harvest for head lettuce and endive. While any leafy green vegetable can be harvested this way, many gardeners prefer to harvest a few leaves at a time as they are needed to extend the harvest period. When harvesting individual leaves, harvest those on the outside of the plant first and leave the inner, younger leaves to continue growing. Avoid harvesting large, overly mature leaves, especially on leafy greens like kale, collards, chard, and mustards. If outer leaves are too large, they can be tough and stringy.
Because leafy greens are consumed raw, they should be thoroughly washed to remove soil or compost to reduce the risk of contracting a food-borne illness. This is particularly important if composted manure was used as soil fertilizer or plants were watered with untreated irrigation water. Store leafy greens in perforated bags in the coolest part of your refrigerator. Most will keep for two weeks in cool, moist conditions. Lettuce does not keep well long-term (a good reason to adopt a harvest as needed approach), but hardier greens like spinach, kale, collards, mustards, and chard can be frozen for longer-term storage.
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