Abstract As part of the continuing search for chemicals which stimulate or retard growth of tree species, the growth regulator N, N’-dinitroethylenediamine (EDNA)2 was applied to red cedar (Juniperus virginiana L.) and to American arborvitae (Thuja Occidentalis L.). Holmsen3 reported that low amounts of EDNA stimulated a broad spectrum of growth increases in many herbaceous plants, including height growth in bean, leaf area in cabbage, dry weight in a rye-grass-clover mixture and protein content in wheat. He also reported that high amounts inhibited height growth of tobacco.