It sounds like you're facing a few classic challenges with your delta maidenhair fern, also known scientifically as Adiantum raddianum. These ferns can be a bit finicky, but once you nail down their preferences, they can really thrive.
Brown and Crispy Leaf Edges: This is often a sign of too low humidity or inconsistent watering. While misting is a good short-term humidity boost, it might not be sufficient if the surrounding air is dry, especially in winter or if you use indoor heating. Consider placing a humidifier nearby or placing the pot on a tray filled with pebbles and water to help increase the local humidity level around the plant.
Leaf Loss and Growth Imbalance: Make sure you're watering evenly—keeping the soil consistently moist, but not waterlogged, is crucial. A good check is to allow the top inch of soil to become just slightly dry before watering again. Overwatering can suffocate the roots, while underwatering can dry the plant out.
Dull Color: This could be linked to insufficient light. Maidenhair ferns prefer bright, indirect light. If the spot is too shady, consider moving it a little closer to the light source, but avoid direct sunlight, which can scorch the delicate leaves.
Pot size and soil condition can also impact growth. Make sure your pot has good drainage to prevent water from pooling at the bottom, which could lead to root rot. A mix that's light and airy—perhaps one-part peat, one-part perlite, and one-part potting soil—can help maintain the right moisture balance. Also, nutrient deficiency might dull the color, so a diluted, balanced fertilizer once a month during the growing season can give it a boost (April through September).
A study published in the Journal of Horticultural Science and Biotechnology indicates that light spectrum and humidity play significant roles in fern health, where both were critical for optimal growth. You might find this adds context to the existing care routine you're following.
Have you checked for any pests like spider mites? These can suck nutrients out and lead to discoloration. They're tiny but can cause significant damage if not dealt with.
For further insights, you might want to explore books like "The Plant Lover's Guide to Ferns" by Richie Steffen and Sue Olsen, which can provide deeper guidance on caring for these and other types of ferns.
Lastly, have you tried adjusting anything yet, and have there been any positive changes? I’d love to hear more about what's working or what other challenges you're facing!