Growing Maidenhair Ferns

Maidenhair Ferns are among the most beautiful plants to grow indoors.  However, few stores sell them because most people struggle to keep them alive. Here is some advice from a biologist.

The basic idea is to give the plants enough water, fertilizer and light to thrive.  But everyone knows that. The difficulty is in the details of the implementation. 

Water

Put the fern in a pot that makes it easy to keep the soil wet.  I usually use 2 gallon pots that have small projections of the feet of the pot into a water tray at the bottom.  To water the plant, you can shine a flashlight into the tray, and if the tray is dry, add 2 cups of water (500 ml) from the top of the plant and the bottom will not overflow.  Under normal conditions, the plants will only need to be watered once a week, but water needs are greater if the plant gets a lot of sun or very hot weather.  With the 3.6 gallon size of the pots, one can add even more water at a time and the plant is even less likely to dry out.  But watering is not quite that simple. Here are the things that can go wrong and how you can prevent them:

• Cracking: if the soil dries out it will develop cracks.  When you add water, it will come out into the bottom tray very quickly, making it seem like the plant is adequately wet.  This problem can be fixed by watering on two subsequent days, allowing the initial watering to rehydrate the soil and re-seal the cracks.  A better approach, however, is prevention: when initially potting the plant to is helpful to press down hard on the soil to make it less likely for cracks to form later, particularly at the edges of the pot.
• Poor wicking: when potting the plant, it is important to have some soil in the pot foot projections that reach to into the water tray.  This allows water to rise by capillary action.  However, if the soil in these projections is packed too hard, it will be difficult for water to rise. 
• High osmolarity: after a year of water and fertilizer, the osmotic strength in the pot will build up.  Plants absorb water by osmosis, which doesn't work if the soil has higher osmotic strength than the plant. Accordingly, you need to flush out the plant with lots of water once a year.  Letting several gallons of water emerge from the bottom of the plant reduces the osmolarity to almost zero.

Light

Maidenhair ferns do best with only a few hours of sunlight a day. If they are very close to a south-facing window they will get too much sunlight and need very frequent watering.  Furthermore, a fern shows its best appearance to the direction from which the sunlight comes.  Accordingly, the best location is in the interior of a room, leaving the plant in the shade for most of the day.  Such positioning also makes it possible for the fern to be viewed from the same direction as it gets sunshine, showing its most pleasing appearance.

Rotating the fern to get growth on all sides is problematic.  The effect is often to get fronds growing in spirals, which are unattractive.

Fertilizer

Plants need fertilizer to get chemicals such as phosphates and nitrogen-containing compounds needed for the plant to grow.  But as discussed above, too much fertilizer can kill a plant by raising the osmolarity.  The best approach is to add a few drops of fertilizer to each gallon when watering. Many diifferent brands of fertilizer should be fine, but I use Miracle-Gro All Purpose Plant Food, which comes as a powder.  I add enough powder to create a saturated solution and then dispense the fertilizer using a medicine dropper.  Adding a bit of food coloring makes the solution more visible.