Trueare spore-bearing plants and should not be confused with flowering plants such as Asparagus, which may well be -like in appearance but are only too often referred to as ferns. The uses of ferns in the greenhouse are many. They are attractive as specimens in their own right, and make excellent foils for flowering plants, particularly orchids, which although they might have spectacular flowers often have less than attractive leaves and stems. Ferns that grow epiphytically can be tied on to bark and grown alongside orchids and bromeliads to give very effective displays.
Ferns can be ridiculously easy or maddeningly difficult to grow. They love humidity and a shady place but hate dryness in the air or at the roots. Direct sun will scorch and yellow them. It is infuriating to find wonderful specimens that have grown themselves from spores under the staging while those in pots receiving all the attention die off. Close attention to shading will always pay dividends.
Although most ferns will grow adequately in an average peat-basedthey prefer a more open mixture. I have found the addition of coarse peat and perlite beneficial. It is not good for them to become too potbound not so much because of the crowding but they are far more likely to dry out. Some which form clumps can be divided and repotted to give new plants.
A Selection of Ferns
Adiantum are the delicate Maidenhair Ferns. A. capillus-veneris is the commonest with light green fronds on wiry black stems. A. raddianum is more robust. The variety ‘Fritz Leuthii’ is often grown. It is very compact, the fronds being bluish-green. There are many other species but few are available. My favourite is A. trapeziforme which has large angular pinnae on its fronds. It is worth looking for it in botanical collections. All are extremely intolerant of dry air.
Asplenium are able to withstand some dry air. There are only two species widely available and both are well worth growing. The cool-loving species is A. bulbiferum from New Zealand, Australia and India. A very graceful fern it will reach 90 cm (3 ft) round. It produces bulbils or plantlets along its older fronds. A. nidus, the Bird’s Nest Fern, is very different having great strapping fronds coming from a central part that is hairy and resembles a bird’s nest. I remember the fern professor at Kew Gardens using a frond as a mask at a fancy dress party. This fern will withstand lower temperatures but needs a minimum of 13°C (55°F) preferably higher to do well. In tropical conditions growth will be very fast and lush. One thing they do not like is uneven watering. This results in new fronds stopping and starting which causes ugly distorted growth. Slugs can be a problem, especially with new growth. Both plants like an open peaty compost.
Nephrolepis are the popular Ladder or Boston Ferns. The species usually grown is N. exaltata and its varieties. Good for either pots or hanging baskets they are graceful and relatively easy to grow. They like perhaps a little more light than other ferns but must have a moist atmosphere. Some plants will send out furry runners from the main rhizomes that make up their root structure. Small plants will form at the ends of these which is why they are so good for hanging baskets when they will sometimes make a complete ball of growth. These small runners can also be used for propagation.
Pellaea rotundifolia from New Zealand and the Norfolk Islands is the Button Fern which has dark green rounded pinnae on its fronds. It can tolerate cool temperatures but is consistent in its dislike of dry air or any kind of drying out at the roots.
If you have space in your greenhouse try growing a tree fern. Dicksonia antarctica from Australia is amongst the commonest grown and can withstand cool conditions easily. Even from spores a fair sized fern can be had in four or five years. Given time they will, of course, become very large as they grow up to 9 m (30 ft) in the wild. A smaller choice would be Blechnum gibbum which has a dark rosette of fronds on top of a 90-cm (3-ft) tall black trunk.
Epiphytic ferns are difficult to control in pots as they seem to spend all their time trying to escape from them by sending out creeping rhizomes which in their turn will bear fronds. Davallia falls into this category. D. canadensis from the W Mediterranean is the Hare’s Foot Fern as the rootstock is covered in brown fur. Very similar are D. solida fijiensis and D. trichomanoides from Malaya. I have used these very effectively on bromeliad logs. They are a little more versatile than most ferns as they can tolerate a certain amount of dry air. Sections of creeping rhizome can be used as, 5-8 cm (2-3 in) long, with fronds attached. These should be laid down on to the compost and nestled into it. Cover the cuttings, as humidity and warmth will help them to grow their own roots.
Another similar epiphyte is Polypodium aureum although this one operates on a much larger scale to Davallia and is most difficult to keep within a pot. I would say it is only worth growing as an epiphyte by giving it a piece of dead tree or bark to cling to. Even in a hanging basket it seems to suffer from claustrophobia and needs to escape. Otherwise it is extremely attractive especially P. a. ‘Mandaianum’ which has a glaucous bluish-green appearance.
Platycerium is a different sort of epiphyte as it does not have the creeping rhizomes. It does have infertile fronds which make the shield-like clasping part at the centre and fertile fronds which spread out and hang in such a way as to give it the name of Stag’s Horn Fern. I have always loved these. The commonest is P. bifurcation from Australia so called because of the way the fertile fronds bifurcate into two parts at the end. The most impressive must be P. grande from Malaya and N Australia which really does make a massive plant. It is possible to grow these in pots but far better specimens will be had by binding them on to boards with a lump of Osmunda fibre at the back. They can then be fixed up high to be admired.
Eventually they will form a colony of their own and be supported by their own rotting infertile fronds which will hold moisture. Watering is something of an art as they will certainly not appreciate being overwatered but will begin to suffer and look shrivelled if underwatered. Liquid feeding is essential in summer as they have no compost from which to extract food, although to an extent they will derive some from their own rotting fronds. They produce spores on the undersides of the end of the fertile fronds which can be tapped on to paper when ripe and sown.
There are two water ferns worth a mention which look similar to large duckweed at first glance. Salvinia natans is very pretty and can be floated on the surfaqe of an indoor pond or tank provided the temperature is warm or tropical. It has no true roots but strange divided leaves that do the same job. It is easy to keep in summer but the old plant dies off jn winter leaving spores produced from sporangia on the lower surfaces. It is best to overwinter them in a pan half filled with loamy compost and topped up with water. If a few plants are floated on this before winter hopefully they will shed their spores which can be stored cool or warm in the loam until spring, when they should germinate, provided the loam has not been allowed to dry out. Azolla caroliniana is very similar and both are in the family Salviniaceae.