The traditional method of producing white clover seed is to grow it in a mixed sward with grass, usually ryegrass. Wild white clover was originally harvested from old permanent pastures, which were heavily grazed, especially in the spring. This system has been perpetuated in the production of white clover seed from leys, and in many areas where sheep and cattle are a major item in the farming enterprise, grazing is an integral part of the system and contributes to the cash return of the ley: seed is not the sole objective. However, the general belief in the advantage of grass companion appears to be so strong that many arable farmers with no livestock produce clover seed from grass/clover swards. No doubt the seed ley on such farms is not only a valuable cash crop but it raises soil fertility and provides an alternative crop in arable rotation. The presence of grass, however, makes the management of successful seed production extremely difficult. Excessive grass growth in spring may result in a serious depression of clover, because of the shading effect produced at certain critical growth stages in the life of the sward.