How to Fertilize Asplenium scolopendrium (Crispum Group)?
Half strength fern foliage feed every two weeks growing season

Asplenium scolopendrium (Crispum Group) · Asplenium scolopendrium (Crispum Group)
Grow outdoors in humus-rich, moist but well-drained soil. Prefers alkaline or neutral soil conditions. Bright midday sun can cause damage. Water moderately when in growth, water sparingly over winter. When in growth apply a half-strength balanced liquid fertiliser monthly. See advice profiles on how to grow ferns
Half strength fern foliage feed every two weeks growing season