Growing Maidenhairs (Adiantums) --
A Collective Opinion

At least two different sources prompted this article about growing Maidenhair (Adiantum) ferns. First, I commonly hear fern growers avoid Maidenhair ferns because "I kill them" and they are "too hard to grow." Second, there was a veritable deluge of opinion on the fern-related e-mail group, the Fernet.

Like most ferns, Maidenhairs tend to grow better when planted in the ground. In fact, they can become a weed. So, this article concentrates on growing Maidenhairs in pots. Two fairly well known Maidenhair experts agree on some general advice. Milton Piedra of Florida, USA, and Chris Goudey of Melbourne, New South Wales, Australia (author of Maidenhair Ferns in Cultivation) agree that most Maidenhair ferns like a lot of bright indirect light, air movement, and humidity. Many Fernetters have their opinions and tips on this topic.

Cynthia Farden of New Jersey offered this:

I've been growing maidenhairs successfully ever since I found out that they don't want to be misted. Keep the soil moist, though. You can also submerge the pot once a week. They love that. I wonder if you're misting the foliage. Try raising the humidity above 50 by sitting the pots on stones in humidity trays. You can also create more humidity by placing wet NZ sphagnum moss around the plant at the soil line. But make sure the soil can "breathe."

Betty Hamilton of South Bend, Indiana, also had some advice:

I have had some success with ferns indoors, and have found that grouping plants together will help increase humidity in the local area ? the more the better. Avoiding drafts & full/bright sun when placing plants is important. Clay pots are good for humidity maintenance, but not for allergies. I too have allergy problems, and moderate humidity of 50% is a compromise, not to encouraging of molds and not too hard on the humidity in the micro-climates created by grouping plants. Good nutrition helps plants (and people) tolerate environmental stress. Keeping plants potted in a container large enough to stay moist for a several days is also helpful. Another consideration is your water. I am now living in an area where the water is suspect (high in minerals Ca, Mg, & Fe, and very alkaline), and don't drink it without filtration. My plants flourished outside last summer, and struggled indoors during the winter. Those plants that went back outside rebounded after the first rain.

Betty brings up two new topics, clay pots and pH, which will come up as continuing themes.

Aurora Vanderbosch in Boston responds to the humidity issues and adds some detail about varieties of Maidenhair. Keep your eye on the Adiantum hispidulum issue.

Maidenhairs are a passion of mine...any variety I can get my hands on, but particularly A. raddianum...and I've discovered that most of them thrive in the windows of my very sunny Boston apartment if I keep the humidity at 70% at all times, and give them a small drink of water each day, with a nice soak, once a week. (All but the hispidulums, which keep dying on me, regardless of my routine!) I also pinch back any limp or crisped fronds daily, so I constantly have new growth coming up. Even with those basic rules of thumb, I have to constantly be on the watch for changes in the environment, as well as to make adjustments for individual preferences. Capillus-veneris seems to like less water and more sun... [A. raddianum] Gracillimum is very finicky and withers if someone thinks bad thoughts its way...Fragrans is fairly easy...Friz Luth tends to crisping...Sleeping Beauty's fronds rot easily...I think you just have to keep trying until you find the one(s) that work best for you under the conditions you find easiest to maintain.

Darrren Andre from Northridge California suggests why several people reported problems with Adiantum hispidulum (Rosy Maidenhair or Rough Maidenhair):

I have found that the hispidulums like it a bit on the dry side (I grow them outside in a rather warm relatively dry(low humidity) interior valley in Southern California and they are one of the few that perform very well.) I would try to water them less (like maybe once/twice a week, tops!)

David Nicholls from Canberra ACT Australia agreed with Darren:

In Oz [Australia], the A. hispidulum I've seen in the wild grow most readily in temperate coastal areas and a bit inland, and also up in the hills in tropical rainforest areas, where the humidity can be anywhere from 20% to 90% or more. It seems to like quite dry soils (within reason) but frosts are a killer.

Robert Arias of Tampa, Florida, answered questions about lime and limestone with two different responses. Here are some excerpts:

Where do adiantums grow in the wild? Usually in very damp places like river banks, limestone cliffs, sinkholes and cave openings. I'd like to put an emphasis on limestone.

Marie Van Ette was going give a talk on maidenhairs at a meeting of the Tampa Bay Fern Club. I went to listen to what she had to say and to ask what I could do to keep these wonderful plants alive. She began her presentation by saying "you know, maidenhairs in general like a limey soil". Well this just blew my mind. In the first sentence she spoke was the answer to most of my problem. I like to grow staghorns, which are acid loving, and I was treating my maidenhairs like staghorns. I have been to swamps where the pH is very low (very acidic), due to the leaf matter built up over time, and will come across a limestone boulder that will look like a fern explosion erupting from the swamp. Also I have found crayfish mounds (crayfish burrow into the ground pushing sand up to the surface where it forms a small mound) where, on older mounds, maidenhairs grow in abundance, but won't be found growing anywhere else. I'm not saying that all Maidenhairs "like" lime, but I've never killed one by putting some crushed limestone in with my potting mix, nor have I seen one "melt" when I've watered with a little lime water. On the other hand I have seen these wonderful ferns burn up after an acid rain when the soil was a bit acidic to start with.

Betty Hamilton provided a little Lime Tea recipe:

I was once told by a very good commercial grower that she supplied lime to her maidenhair ferns, large and small, by allowing an excess of lime to stand in (a jar of) water overnight so that it would be "saturated", then she used this to water the plants, saturating the soil. She would do this spring and fall, or as needed. Small amounts of powdered lime added into the soil mix is far more effective than small lime pebbles in altering the soil chemistry in the desired direction.

Dave Nicholls of Canberra reminds us that we need to do our research on our Maidenhairs:

The comments about ferns in limestone areas in the US are interesting, but seem to run counter to what goes on in Oz. In the Canberra area (SE Oz) the soils are mostly acidic and the ferns (including all the tree ferns) grow in humus rich areas along the creeks. Because there aren't many areas with alkaline soils in this region, the ferns have evidently adapted to acid soils...Near Canberra there are several limestone provinces. On the only one I've looked at closely, there is a unique growth of Asplenium trichomanes. It appears to grow nowhere else, and no other ferns grow on the limestone. Very curious. The two maidenhairs that grow in this vicinity (A. aethiopicum and A. hispidulum) are happy in the normal soil areas.

Keith Rogers of Mannum, South Australia offered a list of tips:

After reading a few of the Maidenhair problems, I realised they were all perhaps suffering from either a lack of air movement, lack of high indirect sunlight, perhaps overwatering, overpotted, incorrect pH problems and poor potting medium and maybe refrigerated air conditioning. Most media require the addition of some composty material, plus some perlite and in most cases for Adiantums, the addition of dolomite lime. The mix should be left in a moist state, in a plastic bag, for a few days to absorb the lime.

Adiantums must be allowed to almost dry out occasionally. Fertilise regularly at half strength.

It is important to note that not all lime is alike and that not all ferns like lime. Keith just mentioned dolomitic lime. The related article on lime provides many important answers about using lime agriculturally.

Betty Hamilton brought back up the issue of plastic versus clay pots.

Are your pots clay or plastic? I have had much better luck with maidenhairs in clay, I think because clay allows lots more air into the soil.

There were several responses to the issue of clay versus plastic. Albert Foster of Georgia, USA gave this advice:

I have yet to find a fern that does "better" in plastic. I move most of mine to clay as soon as possible if I acquire something new in plastic. Even if the plastic is not harmful I like the overall appearance much better, especially as they age in the garden. Also, I feel the air and moisture access to and from the root zone is a plus.

If a species or group like the maidenhair need the more alkaline environment growers can use concrete pots to good advantage. It simulates a limestone environment very well while keeping the soft appearance and aging characteristics of clay. I've used concrete pots for Bostons and a few special cases like Korean Rock Fern that like alkaline conditions.

Christopher Goudey in his book suggested this:

"Many growers are uncertain about whether to use plastic or terracotta plant pots for their Maidehair ferns. All ferns need air at their roots, and this can be achieved by the incorporation of coarse, open materials into the soil medium. Terracota pots allow more air to reach the roots of plants, but are more demanding than plastic pots, as they dry out quickly and need additional watering. Plastic pots are satisfactory, but do not allow the same amount of air to reach the roots of the plants." (p. 20)

Chris went to make this compromise suggestion:

"Growers who favor terracotta pots, but do not want the risk of losing a Maidenhair fern through it drying out, could find it beneficial to double pot their plants. The plants should be potted in the noraml way, in a terracotta pot, being sure to provide the fern with ample drainage. Select a large plastic pot, which will allow ample space to pack at least 3 cm of sphagnum or bush mossaround the outside of the terracotta pot, once it has been placed within the plastic pot. This method has a dual purpose, it not only allows air and adequate moisture to reach the roots, it also keeps the root system at a more uniform temperature."