His interest in plants began around the age of 30 when he was advised by his surgeon to spend time outdoors for the health of his eyes.

The surgeon was Ernst Ludwig Heim, an amateur mycologist and botanist who also influenced Alexander von Humboldt.

Sprengel undertook the study of plants, collaborating with Carl Ludwig Willdenow on his work Florae Berolinensis Prodromus (1787).

While conducting his research on plants, Sprengel appears to have neglected management of the school, which mainly served the rich and powerful.

[1] During Sprengel's time scholars of natural science (naturalists), including botanist Joseph Gottlieb Kölreuter, viewed insects as only accidental or incidental visitors to flowers.

He noticed that the wood cranesbill (Geranium sylvaticum) had soft hairs on the lower part of the petals and came to a hypothesis that they protected nectar from rain in a way similar to those which eyebrows and eyelashes prevented sweat from entering the eye.

[1] Sprengel identified that flowers were essentially organs adapted in their structures to attract insects, which events aided in pollinating the plant.

[1] During his lifetime, Spengel's work was somewhat neglected by his peers, who themselves did not recognize the immanent importance of his findings re the aspects of selection and evolution; but it was also in part rejected because many of his contemporaries viewed as obscene the idea that flowers had anything to do with sexual functions.

Darwin was impressed by Sprengel's approach; it inspired him in his own studies that led to the On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing (1862), where he concluded that nature abhors perpetual self-fertilization.

[3] Important modern successors like Paul Knuth, Fritz Knoll, and Hans Kugler were inspired by Sprengel and advanced the fields of pollination ecology and floral biology.

Kurt Sprengel, Christian Konrad's nephew who also wrote a history of medicine, was nominated to the "Regensburgische Botanische Gesellschaft".