Choy sum turns tough quickly once the yellow flowers open, so harvest when the buds are tight and the stems still snap c

The Problem

Choy sum turns tough quickly once the yellow flowers open, so harvest when the buds are tight and the stems still snap cleanly

For the best tenderness, start checking the plants closely once the central flowering stalk begins to rise. The ideal harvest stage is when the flower buds are formed but still closed, often when the budding stem is about 2-3 inches long and the leaves are still glossy and tender. In many gardens this is around 30-45 days after sowing, depending on variety and temperature. If you wait until the yellow flowers are fully open, the plant begins putting more energy into flowering and seed production, and the stems can become fibrous, chewy, and slightly bitter very quickly.

A simple way to judge readiness is to bend a stem gently. If it snaps cleanly and feels juicy, it is ready. If it bends without breaking, feels stringy, or has a hollow, woody texture, it may be past its best eating stage. You can also look at the buds: tight green buds are good, swollen buds with yellow showing mean you should harvest immediately, and open yellow flowers usually mean the stems will be tougher. A good kitchen portion is about 3-4 ounces, or 85-115 grams, per person as a side dish.

Use a clean knife or scissors and cut the main stem about 1-2 inches above the soil line, or cut just above a leaf node if you want the plant to send out smaller side shoots. In mild weather, choy sum often regrows after the first cut, giving you a second harvest of tender shoots about 7-14 days later. These side shoots are usually smaller but still very good if picked early, often when they are 4-6 inches long. Do not pull the whole plant unless you are doing a one-time harvest, because leaving the base can extend production.

Check the plants daily as they approach maturity, especially in warm weather. Choy sum can go from perfect to overmature in just 1-2 days when temperatures are high, especially above about 75-80°F. If a heat wave is coming, harvest a little early rather than waiting for larger stems. Smaller, tender stems are usually better than big, tough ones. In cooler weather, around 55-70°F, the harvest window is more forgiving, but it is still best not to wait for open flowers.

If you are growing choy sum in containers, keep the plants evenly watered so the stems stay crisp. A pot around 8-10 inches deep works well for a small planting, with several plants spaced about 3-4 inches apart if you plan to harvest young. Let the top 1 inch of soil begin to dry, then water thoroughly until excess drains out. In a typical small container, that may mean watering every 1-2 days in warm weather and every 2-4 days in cooler weather. A common beginner mistake is letting the pot dry completely, then soaking it heavily; this stress can encourage early bolting and tougher stems.

Light also matters. Choy sum grows best with bright light, such as 4-6 hours of direct sun, or bright filtered sun in hot climates. If growing indoors, place it very close to a strong grow light, not across the room from a window. For example, a grow light 6-12 inches above the leaves for about 12-14 hours per day is often much more useful than weak light from a distant windowsill. Leggy, pale plants with thin stems usually need more light.

Another common mistake is waiting for the plant to look like a large supermarket bunch before cutting it. Homegrown choy sum is often at its best when it still looks slightly young. If the leaves are tender, the buds are tight, and the stem snaps, harvest it. Bigger is not always better with flowering brassicas. For planning a meal, 8-12 ounces, or about 225-340 grams, is usually enough for 2-3 side-dish servings after trimming and cooking.

After harvest, rinse the stems and leaves well, especially near the base where soil can collect.

The Result