Botrychium virginianum
Rattlesnake Fern

Ophioglossaceae

Botrychium virginianum

Botrychium virginianum, or Rattlesnake Fern, is a deciduous fern native to most of the United States. It belongs to a group of ferns that retains primitive features, though its fossil record only dates to the Cretaceous. The sterile fronds will reach up to 2½ feet (75 cm) tall, but in containers they very rarely reach over 1 foot (30 cm) in height. The small rhizomes bear only one frond and it is ternately compound and sterile. The reproductive frond somewhat resembles a cluster of grapes. They are very difficult ferns to grow in containers, but do very well in a stable, moist garden setting.

Culture: Botrychium virginianum will grow in a partial sunny location with a moist well-drained soil mix. In the greenhouse, we use a soil mix consisting of 1 part peat moss to 2 parts loam to 1 part sand or perlite. They need plenty of water and may suffer severe damage if allowed to dry completely. They respond to a light fertilizer application only once during the growing season. We use a balanced fertilizer diluted to ¼ the strength recommended on the label. During the winter months, we move the plants to a cold room and keep them at 48° F (9°C), paying careful attention never to let them dry completely.

Propagation: Botrychium virginianum are propagated by division and from spores. Both are very difficult to grow. Division is done in the spring after new growth starts. Carefully divide the rhizome in between 2 fronds. Spores are very difficult to germinate, need total darkness and have a mycorrhizal relationship. Therefore, you must have the fungus in the soil to support the gametophyte. Plants grow very slowly. Although they produce only one frond pair (one fertile, one sterile) per year, they may have primordia for up to 5-7 years already form at the apex.

Botrychium virginianum was featured as Plant of the Week July 23-29, 2004.

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