Wilbur H. Youngman, 89, a retired Agriculture Department seeds specialist and former garden editor of the old Washington Star newspaper, died Jan. 17 at the Manor Care nursing home in Wheaton. He had cancer.

He spent 33 years with the Agriculture Department, where he worked in foreign agriculture services, before retiring in 1959. In addition to being an authority on seeds, he was an agricultural economist. He had worked for the Star from 1938 to 1976. He was the author of the Star garden books, which were first issued in 1944.

In 1958 he received an award from the American Seed Trade Association as the best garden writer in the country. He was a past president of the American Horticultural Society and a director emeritus of the Potomac Rose Society.

Mr. Youngman was a native of Bloomington, Ill. He was a graduate of the University of Illiniois and earned a master's degree in farm management at Iowa State University. He served with the Army in France during World War I, and received the Purple Heart Medal. He taught for two years at Texas A&M before moving here and joining the Agriculture Department in 1926.

In recent years he had taken part in a study on aging conducted by the National Institutes of Health. He was a resident of Leisure World in Silver Spring and was a member of its Inter-Faith Chapel. He had been a member of the Kiwanis, the Masons, and Almas Temple.

His first wife, the former Alice Strode, died in 1961. His second wife, the former Fay Brodell, died in April 1985. Survivors include three children by his first marriage, Dean Youngman of Owensboro, Ky., Jean Hedgepeth of Montpelier, Va., and Shirley McLain of Silver Spring; 12 grandchildren, 18 great-grandchildren, and five great-great-grandchildren.