Christiaan Bernhardus Hardenberg obtained the degree Master of Arts (MA) in entomology at the University of Wisconsin. A comprehensive paper that was probably based on his masters dissertation, "Comparative studies in the trophi of the Scarabaeidae", was published in the Transactions of the Wisconsin Academy of Sciences, Arts and Letters (1907, 55p). He was subsequently employed by the United States Bureau of Entomology and contributed a paper on "The cranberry insects of Wisconsin" to the Bulletin of the Wisconsin Agricultural Experiment Station (1908, 23p).
In February 1910 Hardenberg was appointed government entomologist of the Transvaal Colony, succeeding C.W. Howard*. Following the formation of the Union of South Africa a few months later, the designation of his post was changed in February 1913 to entomologist in the Division of Entomology, Department of Agriculture, under C.P. Lounsbury*. During his first few years in South Africa he was stationed in Pretoria and from February 1911 to August 1915 contributed papers, exhibitions or demonstrations at 13 separate meetings of the Transvaal Biological Society. He served as honorary secretary of the society in 1911, and as president in 1912. When the society amalgamated with the South African Ornithologists' Union in 1916 to form the South African Biological Society, he became a foundation member of the latter. During 1911-1913 he also wrote three articles on insect pests for the Agricultural Journal of the Union of South Africa.
From 1913 Hardenberg was in charge of wattle insect investigations, with headquarters at New Hanover, Natal. He published his findings in a comprehensive paper on "South African bagworms; their transformation, life history, and economic importance", in the Annals of the Natal Museum (Part 1: 1917, Vol. 3(3), pp. 619-686; Part 2: 1919, Vol. 4(1), pp. 143-228), and in Some insects injurious to the black wattle, Acacia mollissima Wild; a report of the work at the field station for the study of wattle insects at New Hanover, Natal, 1913-1917 (Department of Agriculture, Bulletin No. 1, 1918). In addition he discussed the effect of the then current methods of wattle growing on the insect problem in an unpublished paper read before the South African Association for the Advancement of Science in 1916, and in an article in the South African Journal of Natural History in 1920. Other articles by him in this journal dealt with "The study of South African caterpillars" (1919) and "The developmental stages of the brown locust" (1925). He also described a trap-door caterpillar (family Hepialidae) in the Records of the Albany Museum (1919).
Having completed his investigations in Natal, Hardenberg was posted to Johannesburg (1918) and Rita (near present Polokwane, 1919). In 1920 he moved to Lorenco Marques (now Maputo) to take up an appointment as government entomologist of Mozambique. He described his work and experiences there in "Economic entomology in Mozambique and its problems" (South African Journal of Science, 1922, Vol. 19, pp. 285-291). In 1925 he attended an agricultural conference in Maputo, where he spoke on the protection of cotton cultivation.
Hardenberg became a member of the South African Association for the Advancement of Science in 1916 and by 1917 was a member also of the Royal Society of South Africa. He was married to Sigrid Fjoslien, who was also a graduate of the University of Wisconsin.