Seed orchards are established in the same way as clone banks i.e. the planting of grafted clones. The number of different clones is decided upon taking into account desired genetic diversity and the desired projected gains of identified heritable traits. The tree breeding scientists calculate the number of clones and the number of replicates that will, given panmixis, produce seed from natural wind pollination which will provide on average the stated predicted gains. To ensure that the pollination is balanced between clones the planting matrix for the establishment of the orchard is especially designed by tree breeding scientists.
It is important that seed orchards are established at a suitable distance from plantations with the same or hybridising species, to avoid contamination from rogue pollen from outside the seed orchard.
With seed orchard material, given panmixis, there is a high probability that a forest plantation planted with material grown from an orchard will on average (an average across all trees) conform to the stated predicted gains of the orchard.