Athyrium (ath-theer-ee-um) Common-fern Family (Polypodiaceae). Athyrium are tall, graceful, deciduous ferns with compound, lance shaped fronds with numerous leaflets. Athyrium grows best in moist soil with a neutral to moderately acidic pH. Partial to full shade is best. To protect the crowns and tender shoots in the spring, it is best to leave the old fronds on the plant over the winter. They can be removed in the spring when the new fronds reach 6 inches tall. If division is necessary, do so in the spring.