Astragalus sinicus Seeds | Chinese Milk Vetch
LATIN NAME: Astragalus sinicus
COMMON NAME: Chinese Milk Vetch, Zi Yun Ying
Plant Profile
Chinese milk vetch is a low, spreading annual or biennial legume, 20-40 cm tall, with pinnate leaves and umbels of pink-purple pea flowers in spring. It is grown as a green manure and as a forage crop, and it is one of the classic fertility plants of rice paddies in southern China.
The plant forms a loose mat that covers the ground within weeks and suppresses weeds while it fixes nitrogen. It is sown in autumn, overwinters as a rosette, flowers in April and is dug in before the seed sets, when the nitrogen content is at its peak.
Astragalus sinicus comes from China and Korea, and it has been cultivated for so long that its wild range is uncertain. In Japan it is known as renge-sou and is planted as a spring flower in paddies and orchards, where the pink flush is a fixture of the landscape.
Science & Biotechnology
The plant fixes nitrogen through nodules formed with Mesorhizobium huakuii, a symbiosis that is specific to this species and its close relatives. An established stand can fix 100 kg of nitrogen per hectare or more, which is why it is the standard winter green manure in rice rotations.
Milk vetch is also a selenium accumulator, and plants grown on seleniferous soil take up enough of the element to be used in selenium-enriched forage. That property has been studied both as a way to improve animal nutrition and as a route to phytoremediation.
The flowers are a rich nectar source and the plant is one of the first to bloom in spring, which makes it valuable for early bees. The genus also includes the medicinal astragalus, but Chinese milk vetch is a different species and should not be confused with it in preparations.
Uses & Benefits
The main use is agricultural: sown in autumn after the rice harvest, it protects the soil over winter, fixes nitrogen and is ploughed in before planting. It is also cut for forage and ensiled with grasses, and used as a living mulch in orchards.
In the garden it is a winter cover crop for a vegetable bed, and its pink flowers in April are worth the space on their own. It is not a culinary herb, and it should not be substituted for medicinal astragalus. Commercially the seed is a standard agricultural input in East Asia.
Growing from Seed
Sow from September to October at 1 cm deep, 2-3 g per square metre, in moist soil. Germination takes seven to ten days. Inoculate the seed if the species has not grown on the site before, since the specific rhizobium may be absent.
The plant prefers moisture and tolerates poor drainage better than most legumes, which is why it suits paddy margins. Keep it weed-free until it covers the ground, then leave it. Dig it in at flowering in spring, before the stems become woody and the nitrogen begins to move into the seed. In a paddy rotation, broadcast the seed onto the mud before the fields dry, and the seedlings establish without any cultivation.
Our Take
A quiet agricultural plant that earns its keep by fixing nitrogen all winter and feeding the first bees of the year.
Related Reading
If Chinese Milk Vetch appeals to you, these related plants are worth a look: