Keep in mind when planting that Een choy hiyu is thought of as tender, so remember to wait until your soil is warm and the night time temperature is well above freezing before moving outside.
By our calculations, you should look at sowing Een choy hiyu about 28 days before your last frost date.
As Een choy hiyu is tender, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.