Dark green leafy vegetables pack a powerful punch, and many of the lesser-known Asian types are no exception. Apart from a high concentration of vitamins, minerals, antioxidants, and beneficial bioactive compounds, leafy Asian greens also have a diversity of flavors ranging from the mild to hot and spicy with a few other surprising tastes and textures in between. While not as common as lettuce and arugula, gourmet and baby Asian greens are increasingly grown hydroponically as the recognition and popularity of these versatile products grows. It also helps they’re well-suited to hydro growing; most are small, compact plants that mature quickly and can also be grown as micro greens or baby leaf versions. Growers with limited space also have the advantage of selecting some of the newer mini or highly compact hybrid varieties.
Growing Asian greens hydroponically is relatively simple. In fact, it’s similar to growing some more familiar crops. Many varieties happily intercrop with lettuce, herbs, and other vegetative crops as they can use the same nutrient formulation and environmental conditions. Most Asian greens like a moderate level of light and a fairly wide temperature range of 54-79˚F, though bolting is common under excessively warm conditions. They are well-suited to hydroponic systems nutrient film technique (NFT), aeroponics, media beds, and solution cultures such as raft, pond, float, or deep flow technique (DFT).
Kangkong (Ipomoea aquatica) is known by a few other names, including water spinach, water convolvulus, and ong choy. It has a mild flavor more like lettuce than traditional spinach and can be eaten raw or cooked. There are a couple of different types to choose from, including the bamboo-leaved and broad-leaved varieties. Being a sub-tropical plant, kangkong prefers warmer conditions above 77˚F. Given these warm temperatures, kangkong grows extremely fast, particularly in hydroponics. It produces succulent, almost swollen stems and large leaves about three weeks after planting out in an aquatic hydroponic system. It also produces well in NFT, DFT, and raft or float systems.
Shungiku (Chrysanthemum coronarium) is known also as chrysanthemum greens, edible chrysanthemum, and chop suey greens. It has a distinctive mild flavor that becomes stronger and more aromatic as the plant matures. It can be used as a cooked vegetable, in salads, as a pickle component, and in sushi. There are several types of shungiku, all of which produce well with hydroponics. No matter the variety, plants should ideally be spaced six to eight inches apart and grown in temperatures of 64-75˚F with an electrical conductivity (EC) of 1.8-2 to prevent plants becoming elongated and leggy. It should also be harvested while still young and tender (when they reach a height of five to eight inches). While this crop can be raised from seed, shungiku can also be grown on a “cut and regrow” system like most Asian greens. Growers can take cuttings of the shoots every seven days under good growing conditions.
Mizuna and Mibuna
Mizuna (Brassica japonica) and mibuna (Brassica rapa) are Japanese greens that are widely grown worldwide. They have an incredibly fast growth rate under warm conditions; they out-pace lettuce production by several weeks. Mizuna is very mild and has been grown for centuries in Japan as a staple pickling vegetable, though it is also cooked and used in many other dishes. Many hydroponic producers grow mizuna for use in fresh salad mixes. Mizuna plants produce a dense clump of attractive, finely dissected lime green leaves that can be produced under a cut and regrow system. There are also red/purple varieties that develop more intense red pigmentation when grown under high light levels and cooler conditions. Hybrid varieties of mizuna, which are higher yielding and grow more rapidly than open pollinated types, are highly suited to hydroponic production. When grown to maturity, mizuna measures eight-inches tall by 12-inches wide. So, plants need wide spaces and frequent cutting to contain their size and growth. Temperatures for mizuna production range from 32-82˚F. This cold hardiness makes mizuna a widely grown winter crop in Japan and one that is well-suited to unheated growing areas. Maximum growth rates, however, occur at 46-64˚F. Under warm growing conditions, mizuna can be ready to harvest in three weeks. Plants can be left to reach a weight of up to 28 ounces after four to five weeks of growth.
Mibuna is closely related to mizuna, though it has a more rounded leaf shape and slightly stronger mustard-like flavour. Hydroponically, mibuna is grown in much the same way as mizuna for salad green production and whole plant sales. However, mibuna requires a wider spacing of 20 inches between plants, is less tolerant of low temperatures, and is more prone to bolting under warmer conditions. EC levels for both mizuna and mibuna are 1.0-1.4 mScm-1 on a well-balanced vegetative nutrient formulation.
Komatsuna (Brassica rapa var. perviridus), also known as mustard spinach, is a lesser known Japanese green related to mizuna and mibuna. Komatsuna produces extremely well under hydroponic cultivation and is available as both red and green hybrid varieties. Komatsuna has somewhat of a distinctive flavour somewhere between that of a mustard and a cabbage and not at all like spinach. Plants are upright with round leaves, have a good degree of cold tolerance, and are quick and easy to grow.
Misome (Brassica campestris narinosa) is a highly attractive and productive Asian green with a degree of heat resistance, making it a good choice for intercropping with tomatoes, peppers, and other warm-season crops. Growth rates are rapid, with production times as low as 20 days in NFT systems. Under hydroponic production, Misome is typically grown to a young stage as a micro green or for baby leaf salad mixes. The mature plant, with its thick, crisp light green stems, makes a great addition to cooked dishes such as soups and stir fries.
Tatsoi (Brassica rapa var. rosularis), also called spoon mustard or spinach mustard, is an under-utilized Asian green. Individual baby leaves are commonly seen in salad mixes, but the mature plant is short and compact and forms a dense rosette of attractive rounded leaves. Tatsoi is mild in flavour, and it grows rapidly under hydroponic production. If growing mature plants, it’s ideal to space them five to six inches; however, a higher density can be used for baby leaf production.
Pak choi (Brassica rapa spp. Chinensis), also known as bok choy, is one of the most widely recognized Asian greens. With a mild mustard flavour and thick, succulent stems, it’s commonly used in stir fries and soups. Pak choi has both green- and white-stemmed varieties, a wide range of sizes, and those suited to baby leaf production. Newer red varieties of pak choi have an intense purple color that adds contrast to many dishes and an attractive appearance to any mixed hydroponic system. Hydroponic growers should select compact F1 hybrid types of pak choi to avoid issues with plants becoming overly tall, as well as those with resistance to bolting. While pak choi is considered a cooler season plant, these will perform well in most growroom situations if grown rapidly and harvested young.
Asian Mustard Greens
There are many types of oriental mustard greens, including red varieties and those with large savoyed leaves. Mustard is grown for its characteristic hot, spicy flavour. This heat varies considerably between cultivars and with plant maturity and growing conditions. Many mustard types are traditionally used as pickling vegetables, but those grown as baby leaf and rapid-growing micro greens are used in fresh salads. Hydro-grown mustard requires a relatively low EC to prevent excessive peppery flavours from developing and to help prevent bolting. An EC of 1.0-1.2 is suitable, but this can be reduced if required. Many mustard cultivars are also prone to bolting under warmer growing conditions, so consider these cool-season crops. Selecting slow-bolt varieties and harvesting leaves while the plants are still young also helps largely avoid this problem.
Gai lan (Brassica oleracea var. alboglabra), also known as Chinese kale or Chinese broccoli, is characterized by long, thick, tender green stems. It has a mild flavor lightly reminiscent of broccoli with slight bitter overtones. This traditional green is commonly used raw in salads, steamed, or lightly cooked in a similar way to broccoli. Gai lan shoots are individually hand-harvested by snapping it at the base once its yellow or white flowers have formed but before it’s too mature. While gai lan is becoming a popular hydroponic crop, it requires more space than most other compact Asian greens. The plants spread up to 16 inches in diameter and can reach 18 inches tall by the time the flower buds develop and the stems are suitably thick for harvesting. Gai lan grows rapidly under warm growing conditions (64-82˚F), though there are varieties that can be selected for cool cropping conditions.
There are many more exciting and lesser-known Asian greens to be explored and experimented with in the hydroponic system and the kitchen. What’s more, new varieties are continually developed to offer improved colors, faster production times, higher yields, and adaptation to a wider range of growing conditions. Given the diversity, range of flavour, and attractive appearance of Asian greens, it is worth reserving a little space for them in any indoor garden.