The plant we Americans call Chinese cabbage isn’t really a cabbage at all, but from a different, though related species. An ancient Indian oil and spice plant, it spread east to China and Japan, where over centuries of cultivation it was developed into a vegetable crop that is now of central importance to the diet and cuisine of those countries. There are two basic kinds of Chinese cabbage: a heading kind, also know as Napa Cabbage, which is what we will call by that name, and then a kind which has highly developed stems and is known as celery cabbage or pac choi / bok choy.
There are four types of heading Chinese cabbage. A given cultivar can have a wrapped-over head, not unlike a European cabbage though taller, or a joined-up head, which is more open-hearted. Furthermore, each of these can be either a short, stocky barrel-shaped plant, or tall and cylindrical. Aside from their shape, though, all four kinds are remarkably similar. They have pale green leaves with a diaphanous crepelike texture, and are lightly savoyed, or ruffled, at the edges.
Napa cabbages grow best in cool weather, and thus like most European cabbages are more adapted to either spring or fall planting, than to mid-summer. In general, though, the wrapped-over types are more heat-tolerant and earlier to mature, while the joined-up types tend to be less compact, later to mature, and more cold-tolerant. From this we can deduce that the former are better for spring and the latter you’re best bet for fall planting.
Pac choi is a non-heading plant with highly developed petioles (leaf stalks) and relatively small spoon-shaped leaves that begin about halfway out the petiole rather than right at its base. The leaves are smooth, shiny, and more succulent than Napa cabbage, more like a chard than anything else. Here again, though, there are four basic types. One type has narrow petioles with a round, celery-like cross-section. This is thought to be the original, ancient form of the plant. Then there is a type that has wide, flat petioles. Within each type are cultivars with either green or white, or more recently, red petioles. Pac choi is generally more heat-tolerant than Napa cabbage, though the types do differ: those with white petioles are generally grown for fall harvest, while the green petiole types are slower-bolting and therefore better adapted to spring planting for summer harvest.
Both Napa cabbage and pac choi like the same rich, well drained, slightly alkaline soil as the other members of the cabbage family. The basic problem you’ll face in growing either kind is that although they prefer cool weather, they will almost certainly bolt if regularly exposed to temperatures below 50º F when young. The rule-of-thumb in this case is that more than a week of cold weather when they are in the four- to six-leaf stage will cause the plants to run to seed. While new cultivars can take considerably more temperature variation, you still need to pay close attention to the weather in order to set the proper schedule for planting and harvest.
Spring crops, due to the regimen of early cool temperatures, increasing day length, and warm-to-hot temperatures at harvest, are more prone to failure than fall plantings. In our experience the keys to success are: (1) start from transplant, but only individual cells or soil blocks, so as to avoid shocking the plants when they are moved to the garden, and (2) fight your spring fever; that is, don’t start too soon. Both Napa cabbage and pac choi should be started around the same time as Brussels sprouts (about a month before the last spring frost).
The same timing applies if you are sowing directly in the garden, but never plant before the soil temperature reaches 50º F; that is almost certain to cause bolting. You can check this with a soil thermometer (make sure the probe is at the level the seed will be placed by the planter, not deeper or shallower). For fall planting start about 60 to 70 days before the first fall frost (or the onset of cool weather if you live in a hot climate). Gardeners in cool summer climates can likely grow pac choi right through the summer, planting every two weeks or so for a continuous harvest. Whatever the schedule, the seed should be set ¼ inch deep in cool moist conditions, and up to ½ inch deep if the weather is hot and dry.
Napa cabbage and pac choi share the same diseases and pests as other members of the cabbage family, though in our garden they are especially attractive to flea beetles. I cover the first spring crop with a floating row cover. That both keeps out the flea beetles and helps moderate temperature and moisture to lessen the choice of bolting.
Spacing for these two crops are quite different, as the plants are radically different in size. For Chinese cabbage, allow 18 inches per plant in rows two to three feet apart. If you plant in beds they can be set 18 inches apart in an equidistant pattern; on our three-foot-wide beds that is a 2:1:2 pattern. Pac choi can be grown much closer, with row spacings as little as six inches, in rows 18 inches apart, or 6 inches equidistant in beds. In the same three-foot bed this would be a 5:4:5 pattern. Pac choi can also be broadcast-sown in well-prepared beds and harvested as a seedling or salad crop a scant two weeks after germination, when the plants are only 4-6 inches tall.
Napa cabbages can be harvested anytime after the heads firm up. They should be solid in response to a hand squeeze. Spring crops need to be harvested promptly to avoid problems with bolting or head rot; fall crops need to be picked before hard frost. Pac choi is ready for harvest anytime after it has four or five leaves. The stalks can be harvested individually, or the whole rosette cut off below the crown. Thinnings make a great addition to salads. With both kinds, the flowering sprouts are themselves edible, so even a bolted plant is worth having. Just don’t let it set seed or you’ll be pulling young plants as weeds for years to come.
Some good Napa cabbages for spring and fall planting are Dynasty, Two Seasons, and Spring A-1, all squat, barrel-shaped cultivars, and Green Rocket, Monument, and Jade Pagoda, which are tall and cylindrical. My favorite pac choi is a dwarf green hybrid named Mei Quing Choi, by far the best tasting and slowest bolting of all the ones I’ve grown. Two decent white-stemmed cultivars are Le Choi and Prize Choy. They are quite similar in appearance, but Le Choi has a much stronger mustardy flavor. One last Chinese brassica I like is Tatsoi, which is a close relative of pac choi and looks like a very dark green, cabbage-leaved, loose-leaf lettuce. It is the most bolt-resistant of all these greens, and should be grown 18 inches on center and harvested stem by stem like parsley. South of USDA Zone 5, it will overwinter with kale, providing a good sources of greens through the cold months.