I have had a crispy wave fern for a couple of months now and its overall health seems pretty good with the exception of one leaf that has a skeletal look, see the picture below. It seems to propagate down very slowly. Any idea at what this is and if I should do anything about it? Thank you!
It appears you have a watering problem. You are probably keeping the soil to wet, in a effort to keep it moist. It is true that ferns, even Crispy Wave Fern, AKA Asplenium nidus, like moist soil, but moist is the key word. They do not want wet soil.
If you recently purchased your plant you should know, the professional growers often grow these plants in pure peat or coco coir peat. Both these mediums hold a great deal of moisture/water. In greenhouses this amount of peat or coco peat will work great, but in a home environment it is very easy to over water with this amount of peat.
If you have never replanted it, the soil will hold more moisture than you want. EVen if you have repotted it, it maybe holding too much water. Crispy Wave Ferns never want to be wet, just constantly moist. This means when you do water give it less than you would think. Wait an hour and check to see if the soil if fully moist. If it appears to still be too dry give it a bit more water.
You are going to want to water your fern more often, but with less water. This way you keep the soil moist not wet. If this is the only sign of over-watering, then you have caught the problem in plenty of time. Make sure from now on you follow these watering instructions.
If uncertain if the plant is too wet or too dry, use a bamboo barbecue skewer to check for you. Insert the skewer in the soil for 30 min. Then pull it out and check it. Look at it and touch it. If the stick is dry, you have waited way too long before watering. IF the stick is wet, you over-watered last time and need to wait longer before you water again. If the stick is moist, you can add little water, but never lots. Remember less water more often.
In spring I would recommend changing the soil if you have not done so already. It is best to wait until spring. Use a soil that is made up of peat with lots of perlite. You may want to buy a bag of perlite to add a little more. This plant grows in very loose soil or log or rotting trees. This is very moist, but loose soil. You want your potting mix to be loose, but still hold water. So, not more than 30% extra perlite to the mix you buy.
The mix you buy should be an indoor plant potting mix or grow mix. This is will sterile soil. If will also have lot of perlite. It may not need any additional added to it. But, you need to decided how often you want to water. The more perlite you add the more often you will need to water, but the less likely it will be that you over-watered. Too much perlite and you risk under-watering.
Ferns will survive a few over-watering, if they are spaced out, not back to back over-watering. Many ferns like you fern will not tolerate being completely dry, so it is important you decide how often you want to water.