Guide to growing Pilotweed - Silphium
Silphium are tall hardy perennials that range from 1.5M to 3.6M in height.
They come into bloom from midsummer through to early autumn when they carry flowers reminiscent of sunflowers in yellow.
Their large size means that Silphium can be grown at the back of a garden border.
Some common names for members of the Silphium genus include Pilotweed, Cup Plant, Rosinweed, Indian Cup and Compass Plant.
How to grow Pilotweed
When growing Pilotweed from seed it is best to sow them outdoors using fresh seed in the autumn. The Pilotweed seed should be chipped, and sown at a depth of 12mm into a flat. The flat should then be sunk into the ground in a completely shaded part of the garden; next cover the flat with glass. Germination should take about three weeks. The plants can then be transplanted into either a sunny or partially shaded part of the garden in the autumn; or bring the flats indoor for the winter and transplant to the garden in the spring. Ideally the soil that Silphium species such as Pilotweed grows in will be slightly acidic to neutral (pH5 to 7) and moist.
Caring for Pilotweed
It is fairly easy to look after Pilotweed, Rosinweed, and other Silphium plants; they like a moist soil so water frequently; every spring apply a fertilizer that has a low nitrogen count. Silphium are large plants so supply a stake. Every three years or so divide the plant to maintain vigor. If you require more Pilotweed plants then they can be propagated by division, this should be carried out either in early autumn or spring.