Direct-seed choy sum into well-tilled garden beds that have been amended with a 2-inch layer of compost. Plant seeds 1/4 to 1/2 inch deep Choy Sum seeds will germinate between 7 and 10 days Thin the choy sum seedlings to 12 to 18 inches apart Choy Sum leaves can be picked individually as they grow or the whole plant can be harvested about 7 to 9 weeks after sowing. If the plants bolt before reaching full size they can still be eaten, the yellow flowers are edible add a mild peppery taste.