How to Grow Choy Sum / Yu Choy

Welcome to our How to Grow Chinese Vegetables series: Choy Sum edition! In this post, we’ll talk about how to grow choy sum or cài xīn (菜心), AKA yu choy or yóucài (油菜).

We have professional insights from Christina Chan, farmer and owner of Choy Division, a regenerative Asian vegetable and herb farm in the Hudson Valley, who has generously offered to share her expertise with us and our readers for two seasons now.

WHAT IS CHOY SUM?

Choy sum belongs to the Brassica genus of vegetables, also known as the cabbage family. It is native to southern China, with some tracing its origins back to Guangdong, China (Canton).

People often confuse it with bok choy or Chinese broccoli, but it generally has longer stems that are more cylindrical than bok choy, and they’re more tender than Chinese broccoli. It may also be called “flowering brassica,” as it has distinctive bright yellow flowers.

Yu Choy (油菜) translates to “oil vegetable,” because certain varieties are primarily grown for their seeds to produce oil. Did you know that canola oil is actually refined rapeseed oil?

In China, you might see cài zǐ yóu (菜籽油), which is a less refined version.

Indeed, sometimes you’ll see yu choy being translated in English to “rapeseed.” The vegetable’s other name, choy sum (菜心) translates to “vegetable heart” or “cabbage heart.”

You can buy them tender and young (yu choy miu), which is suited to stir-frying, or as larger more mature stalks (great for blanching and drizzling with sauce, as in our Easy Yu Choy recipe). We’ve even made it into pesto! (See our Choy Sum Pesto Pasta.)

Like any leafy green, it’s rich in fiber, vitamins, and minerals, and great for you!

Choy Sum Varieties TO TRY

Christina suggests trying these varieties from the following seed sources:

• Green 70D improved (Johnny’s Selected Seeds): Sweet and tender, can be harvested as a cut and come again crop.

• Early Green (Kitazawa Seed Co.): an early variety great for harvesting young. Tolerant to downy mildew, though somewhat sensitive to low temps. Best for late summer/fall growing.

We grew “Early Green” in our garden!

Ideal Growing Conditions for Choy Sum

Climate/Weather

Like other leafy greens, choy sum grows best in cooler weather. Here in the Northeast, you can grow it in early spring or fall. We have found that fall yields better harvests with less pest damage and bolting.

These vegetables hate heat, and are prone to bolting (setting seed) if it’s too hot. It also tends to grow faster in warmer weather with longer days, resulting in skinnier stems. For fatter stems, grow them in fall, when temperatures are dropping and the days are getting shorter.

Sunlight

Choy sum enjoys cool yet sunny conditions. This is another reason while fall is ideal!

Soil Conditions 

Choy sum grows best in fertile, moist, but well-drained soil. If you’re growing it later in the season, be sure to amend your soil with compost before planting, so that the vegetables have enough nutrients to thrive.

Brassica crops are also best rotated after legumes, which add nitrogen the the soil.

Germination will happen faster when the soil is warm (as in late summer/early fall), and the plants will grow and mature quickly—in about 30 days!

How to Sow Choy Sum Seeds

Christina recommends direct sowing your choy sum into their final planting position. You can grow these in containers or raised beds as well as directly in the ground.

Starting them as plugs and transplanting them isn’t recommended, as the transplant shock makes them more likely to bolt.

The best time to plant choy sum is in late summer/early fall, when temperatures are gradually cooling, but while nighttime temperatures are still consistently above 55°F (12°C). These cooler nighttime temperatures help develop the sugars in the vegetables, making them sweeter and tastier.

Amend your soil with a couple inches of organic compost or other nutrient-rich organic material. Sow the seeds 1-inch apart, in rows about 1 foot/30cm apart, with the seeds 1/4-inch/6mm deep. Water them in, and watch them grow!

Harvesting Choy Sum

If desired, you can actually get multiple harvests of choy sum as a cut and come again crop. Do the first mature harvest once the plants are about 8-10 inches (20-25cm) tall. Cut them at the lowest node, where the plant is still tender. The plant will then continue to produce side shoots from the remaining nodes.

Alternatively, you can cut them as baby plants as early as you like. These are very tender and sweet!

Generally, we harvest choy sum before they begin to flower, but if you would like to harvest them while flowering, be sure to do so soon after the flowers appear, or the vegetables will begin to become tough. Once flower buds appear, you have about 1 week to harvest.

Problems & How to Manage Them

Here are some common garden challenges you may have when it comes to growing choy sum, from premature bolting, to pests and weeds! These issues are similar or the same as those with other brassicas like bok choy.

1. Bolting

“Bolting” is when a plant under stress begins to flower prematurely and then sets seed. It will stop growing new leaves, putting all of its energy into reproducing (i.e. producing seeds), and then die.

This can be caused by hot weather, very cold weather/frost, or drought. To prevent this from happening, plant in late summer/early fall when weather conditions are a bit more stable and starting to cool down. You want a 30-day time period in which nighttime and daytime temperatures are likely to stay between 50-80°F (10-26°C).

Harvesting early can also ensure you get a good crop before the plant starts to bolt. 

2. Pests 

Common pests around brassicas include flea beetles, white cabbage moths, and slugs/snails. All of these pests tend to be greater problems during spring, so the first thing you can do to avoid them is to plant in fall. Let’s go into each in more detail: 

Flea Beetles: These are tiny, jumping, shiny black beetles that eat tiny holes in your brassica leaves. They might only cause cosmetic damage, and your crop can still be edible. However, if they’re really bad, they can skeletonize the leaves and stress the plant—especially when young.

Here in the Northeast, they are worse in spring than in fall. We have personally also found that planting in raised beds leads to less flea beetle damage than planting out into open ground. Floating row covers can also help keep them off your crop.

Cabbage Moth: As caterpillars, these moths will eat right through young leaves, leaving behind chewed holes and dark green droppings that look like small pellets. 

The way to avoid this is to cover your crops with floating row covers upon planting, so that the adult moths can’t get to the plants to lay their eggs. You can also physically remove any caterpillars as you see them, but prevention is best!

Slugs & Snails: Slugs and snails both enjoy eating the young, tender leaves of all cruciferous vegetables, especially in moist areas where they thrive.

Clean up any rotting wood in your garden, which are common slug habitat, and put up a physical barrier around the crops. We use dried spiky gum balls from our sweet gum tree, but you can also try copper tape or other barriers.

3. Weeds 

We find that hand-pulling weeds while they’re still small is the most effective management technique. This is the best method for removing the entire root system to prevent any regrowth. Don’t let your garden go too long without a bit of light weeding, and you’ll end up doing less work overall throughout the season.

It’s also best to catch weeds early (even before the growing season begins in earnest). Hand-pull any emerging weeds in early spring, and then add a thick (at least 3-inch/7-8cm) layer of organic compost as a mulch. This prevents light from getting to the young weeds and amends the soil at the same time. 

We also find that the no-dig method (just layering compost on top of the soil rather than tilling it in) helps prevent weed seeds from getting exposed to light, and after a couple growing seasons of this, we see much fewer weeds emerging!

Conclusion

We hope you enjoyed this post on how to grow choy sum and that it helps you grow your own crop of leafy greens in future!

Any lingering questions? Feedback on the post? Stories or tips of your own to share? Let us know in the comments below!