The size of the seed orchard is determined by the seed demand and the expected seed production from the orchard. Both figures are subject to estimates. Planting targets may be altered in the future and the seed production from individual trees are often only subject to qualified guesses. A minimum of 15–25 clones or families to assure a sufficient genetic base and limit selfing should be used.
A seed orchard can in theory be operative as long as the trees are physiologically capable of producing seeds. In practice, however, a seed orchard will only be operative until a new improved seed orchard has been established, based on next generation progeny test. Seed orchards are usually referred to by generation, 1st, 2nd, 3rd, etc.
