These accessions consisted of more than 350 species and 114 genera. In 1946, the trees and shrubs that appeared to be the best adapted and to have the best potential for conservation plantings were planted in uniform test blocks. Each planting contained essentially the same species, grouped on the basis of potential conservation use. Thus, each new species was readily compared to plants that had the same potential use. A species that was in common commercial use was also planted in each group as a check or control.
Moisture is the most critical factor in the survival of trees and shrubs in the intermountain area.
The native vegetation is predominantly grasses and forbs. If allowed to compete for moisture, these well adapted plants will quickly eliminate the tree or shrub. Therefore, most test plantings, even under irrigation, were clean cultivated. Tillage was kept. A perennial cover crop of red fescue, Festuca rubra , was seeded in the irrigated plantings at Prosser in 1953.