Marshallia grandiflora, Bog Buttons- Marshallia thrive under much the same care as Pitcher Plants, Venus's Flytrap, Bog Orchids and many other bog plants. A soil of 1/3 sand plus 2/3 peat moss works well, although many soils can work as long as they are acidic, hold moisture and drain. Keep the plants moist to wet but not flooded as this can cause rot. When planting, keep the crown above the soil and gently firm the soil around the roots or use a gentle stream of water to settle the soil.
Full sun is best, although Marshallia can tolerate 30% shade. The plants may tolerate greater shade, but may not perform as well. We're not sure how cold this species can survive, but we've had them sub-freezing, to U.S.D.A. Zone 6. The plants can get crowded after time and benefit from dividing the clumps in early spring. Removal of dead foliage is also a good idea. Do not mulch over top of the plants or they may rot.
Fertilizer is seldom needed, but a 1/2 strength solution of Miracid™ or similar fertilizer can help. If the plants look healthy and bloom, it's best not to fertilize them. Seed heads can be removed after the flowers fade or left to mature for planting. The seeds sprout best after a cold and damp stratification which simulates the passing of winter.