Compass plant (Silphium laciniatum) is one of the classic tall grass prairie species. At one time widespread, due to the cow and the plow it has been virtually extirpated from most of its range. However, with patience it can be readily established in dry-mesic to mesic prairies.
Compass plant is noted for its deep root system and the long life span of individual plants. Under favorable conditions plants may flower in the second or third growing season, but prairie plantings from seed may require more years to flower.
In our planted prairies, compass plant did not begin to flower until the fifth or sixth year. In the first growing season it may only produce a single leaf. The second growing season there may be two leaves, and by the third season several larger leaves are formed. During these early years, most of the growth of the compass plant is subterranean, as it sends down a very extensive tap root. Measurements made in tall grass prairies have found root depths of 9 to 14 feet!
Compass plant leaves are highly dissected, and are so distinctive that even a single small leaf in a new prairie planting is easy to identify. The name "compass" comes from the idea that the leaves align themselves in a north/south direction. Perhaps, but I have found leaves of individual plants aligned in other directions as well.
Because compass plants begin flowering in early July, they are often the tallest specimens in a planted prairie.
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