7 CFR § 201.77 - Length of stand requirements.
(a) Alfalfa. Limitations on the age of stand and certified seed classes through which a given variety may be multiplied both inside and outside its region of adaptation shall be specified by the originator or his designee. Certified seed production outside the region of adaptation shall not exceed 6 years if not otherwise specified by the originator, or his designee.
(b) Red clover. Only two seed crops are permitted of all certified seed classes.
(c) White and alsike clover. Only two successive seed crops are permitted following the year of establishment for Foundation and Registered classes, but 2 additional years are permitted if the field is reclassified to the next lower class. Four successive seed crops following seeding are permitted if the first and succeeding crops are of the Certified class, provided the stand of perennial plants is maintained.
(d) Sainfoin. All certified seed classes are eligible to produce five successive seed crops following seeding.