Brassica rapa var. chinensis. Yu Tsai Sum is a type of choi sum. This summer crop is also known as Yu Choi. Grown for tender flower bud stalks (yellow flowers) and glossy, bright green leaves, it is mild and sweet when cooked briefly. Stems will be 0.5-1cm (.25") thick if grown and watered well. This variety was tops in our trials for both taste and texture. For large plants, sow in rows 30-45cm (12-18") apart. Cut the flower bud stalk with a few leaves - new shoots will grow from a leaf axil. Plant Yu Tsai Sum seeds in early summer, up to 6 weeks before frost. Early spring plantings may bolt.
Matures in 40-60 days. (Open-pollinated seeds)
These cool-season vegetables are incredibly easy to grow and very tasty. The leaves can be used raw in salads, or the whole plant can be steamed or stir-fried. Both types require regular watering and a watchful grower – plant repeated short rows, and be sure to harvest them before they bolt. Continue reading below to learn how to grow pac choi and choi sum from seed.
Brassica rapa chinensis
We Recommend: Mei Qing Choi (MU553). For growers particularly, this hybrid variety is surprisingly uniform in timing and growth. The plants are beautiful and upright with crisp stems and very good flavour. It works well in the home garden, but sow short rows repeatedly, or you’ll be overwhelmed by it all coming at once.
For Urban Gardeners: Toy Choi (MU522) works very well in containers and raised beds. It’s compact to the point of being cute, but tastes wonderful raw or cooked. Very nice, crunchy, succulent stems.
Season & Zone
Season: Cool season
Exposure: Full sun to partial shade
All are cool season plants that grow quickly and then bolt. Direct sow with frost protection (a cloche or heavy row cover) as early as late winter, or without protection from four weeks before the last frost date to eight weeks after. Sowing short rows every 2-3 weeks allows for a fairly constant harvest time. Sow again in late summer, and provide frost protection as the first frost date approaches.
Sow 3-4 seeds 5mm-1cm (¼-½”) deep in each spot you want a plant to grow. Thin to the strongest plant at a spacing of 15-20cm (6-6″) between plants in rows 30-45cm (12-18″) apart.
Days to maturity: From direct sowing.
Ideal pH: 6.0-6.8. 1 cup of complete organic fertilizer will provide sufficient nutrition to 3m (10′) of row. Choi Sum is harvested just before it flowers, so keep a close watch on each row. Pac Choi can be harvested at any stage, but if you want full-sized plants, watch for signs of bolting. Flower buds will appear at the centre of each plant, and a stem will form quickly as the plant turns from urn-shaped into a tall cone. Harvest as quickly as possible once flower buds are visible. Keep plants well-watered throughout their growth.
Use a sharp knife to cut the plants at ground level when they are ready to harvest. They will not grow back like some other crops, so plant several short rows every couple of weeks for a longer harvest.
In optimal conditions at least 70% of seeds will germinate. Usual seed life: 3 years. Per 100′ row: 260 seeds, per acre: 114M seeds.
Diseases & Pests
Slugs and woodlice (sow bugs) may nibble young seedlings. Keep the garden free from debris and excess water, where both of these pests like to go during the day. Protect plants from flea beetles and cabbage moths with lightweight row cover.