Growing Guide: Ferns
The fern craze of the Victorian era reached a peak when Wardian cases allowed tender ferns to be grown in the home rather than in steamy stovehouses. Interest waned in the early part of this century and it is only now, 100 years later, that improved building methods and centrally heated homes have encouraged us to grow ferns in our homes once again.
Ferns differ from other plants in that they are non-flowering and so are unable to produce. Instead, dust-fine spores are formed in tiny sporangia, or spore sacks, on the underside of fertile pinnae.
Some fern species are readily available in florists, others need to be searched out. But no matter how they are obtained, the grower is sure to be rewarded by the varied appearance of these attractive plants. Most ferns grow well in cool to warm rooms (15-21°C/59-70°F) provided they also have good light,around their fronds and moisture at their . The idea that being woodland plants ferns need a dark corner is wrong. Most indoor ferns are native to sub¬tropical and tropical areas where light intensity is high even below trees. A windowsill facing east or north is, therefore, a good for them, and some like fluorescent lighting.
High humidity is important for the dry atmosphere of modern homes makes for unhappy plants. A daily spraying will help or stand the plant on pebbles in a dish of water. The ‘pot in a pot’ method, whereby the potted fern is placed in a larger pot 01 con¬tainer and moist peat packed around it, also raises humidity levels.
Themix needs to hold moisture yet at the same time be well drained. Two parts sterilized -mould, one part sterilized loam and one part gritty sand plus small pieces of charcoal generally make a good fern soil mix. However, any peat-based mixture may be used.
Although not heavy feeders, ferns do need a regular weak liquidevery two weeks during the growing season especially if growing in a peat-based medium which incorporates a limited amount of fertilizer. It is preferable to use a high nitrogen fertilizer as is usual for foliage plants.
There should always be moisture at the. Only if the -ball has dried out should a fern stand in water and then only for a limited period before draining. Some ferns, such as Stag Horns, appreciate this treatment but the majority do not and quickly suffer root damage if dried out or saturated with water.
The increasing use of plasticmeans that fewer clay pots are made today. Porous clay pots have the advantage of producing a humid climate below the foliage but with plastic pots other humidity methods can be used. Ferns grow happily in either pot and some, such as Adiantums and Nephrolepsis, also grow well in hanging baskets. So it can be left to the grower’s preference as to which type is used. When the root-ball fills its pot the fern should be repotted and springtime, before new growth commences, is best for this. Judicious root will allow a large fern to be replaced, with fresh potting mix, into the same or next size pot.
Many ferns may be propagated by division of the rhizome. Some, such as maidenhairs, may be broken apart and pieces of young rhizome with a few fronds and roots potted into small pots. Others, such as Humata, need longer pieces of rhizome with a growing tip to be rooted.
For more adventurous growers, propaga¬tion by spores is more interesting. The life-cycle of a fern is not as simple as it might appear for it is not a spore that grows into a fern. Given warmth, moisture and light a spore will produce a prothallus which has female and male organs on its underside. Male cells swim to fertilize female cells and from a fertilized cell a sporophyte grows.
To grow from spores a clean pot is filled with a well-moistered sterile medium such as peat. Fern spores are scattered onto the surface and a clear glass cover is placed on top. The covered pot should be put in a warm place. After a few weeks a green film will cover the growing medium and several months later the heart-shaped prothalli will be seen to have thin erectgrowing from them, the sporophytes. When large enough to handle, the baby ferns should be potted up and kept in a humid atmosphere.
Ferns have two major pests, scale and eelworm. Most pesticides are phytotoxic to ferns so scales should be picked off or brushed with methylated spirits or rubbing alcohol. Eelworm attack shows in blotched, stunted foliage and severely attacked ferns should be burned. Slight attack may be remedied by immersing the whole fern, washed clean of soil, in hot water (50-52GC/ 122-125°F) for five minutes.
Adiantum 7°C/45°F min; Sub-tropical and temperate zones
A. capillus-veneris (Venus’-hair or) Many species of Maidenhair ferns are similar in appearance, having wiry black petioles (leafstalks) growing out of a quickly spreading horizontal rhizome. This species grows to a height of 20-30cm/8-12in and the petioles carry many branched fronds of delicate fan-shaped pinnae which are pale green in colour. In mature plants the undersides of the pinnae are edged with brown sori (clusters of sporangia), giving extra colour to the fern. It is a fairly easy fern to grow when a humid atmosphere is provided around the pot to prevent shrivelling. A daily fine spray of tepid water is a help or the pot in a pot method should be used. Direct sunlight should be avoided; however, the plant should not be placed in a dark corner. A north or cast-facing windowsill is ideal.
A. cuneatum (syn. A. raddianum) This Brazilian species is very similar in appearance to A. capillus-veneris although a little larger, growing to 50cm/l§ft in height. The pinnae are also coarser. However, it is not always easy to distinguish between the two as there are several cultivars of A. cuneatum which vary in size and also in colour from yellow-green to dark green.
A. hispidulum (Rosy Maidenhair) This species is different in appearance, the young foliage being reddish-brown in colour changing to medium green with age. The petioles are covered with dark brown scales and the plant grows to about 30cm/1 ft in height. The frond blade looks more like the spread fingers of a hand, not branched nearly as much as in the other Maidenhair species, and pinnae are longer.
Maidenhair ferns are easily divided bythe rhizome into pieces, each with a few fronds and roots. Pot these into peaty potting mix in a smaller pot.
Asplenium Spleenwort; 13°C/55°F min; Australia/New Zealand/Far East
A. bulbiferam Deeply serrated pinnae spread out in a triangular shape from a black petiole and rachis to make a frond which can be up to 60cm/2ft in length and 23cm/9in wide. Fertile pinnae produce sporangia on narrow segments of the serrations while sterile pinnae have broader segments. Inter-mixing of fertile and sterile pinnae on the same frond gives added interest to the shape. The appearance of this fern can be rather bizarre forthat are miniature editions of the parent plant grow from bulbils produced on the upper surface of the pinnae. Thus new plants are easily propagated by placing a pinna with bulbils onto moist peaty potting mix. Roots are quickly formed and the plantlets soon grow independently.
A. nidus (Bird’s Nest Fern) This fern forms a definite rosette. The simple, entire blades are glossy, light green in colour and have a black rachis running the length of the frond. They unfurl from the centre of the rosette which is covered with a dark brown bristle-like scale. Depending upon growing conditions, the fronds can be anything from 30-120cm/1-4ft long and 5-20cm/2-8in wide. Warmer and more humid conditions give the larger plant. Sori forming a fishbone-like pattern on undersides of mature blades shower a mass of light brown spores on to lower fronds.
Cyrtomium falcatum Syn. Polystichumjalcatum; Fish-tail Fern; 7°C/ 45°F min; South East Asia
The upright fronds can grow to 60cm/2ft long and they have silver furry scale covering their petioles. About 12 pairs of dark green glossy leathery pinnae form the blade, each pinna being similar in shape to a holly leaf Sporangia are scattered irregularly over the underside of the pinnae and first appear as very small green spots changing to light brown with maturity. The cultivar ‘Rochfordianum’ (Holly Fern) is more compact growing, 30cm/1 ft , with larger pinnae ideal in a living room. These ferns are said to
be indestructible, but perhaps a better description would be that they are more tolerant to lower temperatures and humidity.
Davallia 5X/41cFmin; Far East
D. bullata (Squirrel’s Foot Fern) The furry rhizomes, which give this fern its common name, spread quickly and a mass of dwarf fronds shoots up from them. The blade is triangular in outline, dark green and the pinnae are deeply cut. A rhizome tip when laid on moist potting mix will root quickly and then rapidly divide to cover a small hanging basket. It is a very tolerant plant, not objecting to the dryer atmosphere of a modern home and even liking a little sunlight.
D. canariensis (Hare’s Foot Fern) A small popular species with thick rhizomes that are pale brown in colour. The leathery fronds are mid-green and finely cut. D. fijiensis This species has a much freer habit of growth. The fronds are larger, lighter in colour and appear more delicate and finely cut.
Humata tyermannii Bear’s-Foot Fern; 7°C/45°F min; West Africa
Small rhizomes covered with white furry scales divide frequently and a frond is sent up every 5-7.5cm/2-3in. When young the frond is rosy-green turning to very dark green with age. The blade shape is like a long pointed triangle 15-23cm/6-9in high and up to 12cm/5in wide at the base. The pinnae are finely cut. It is best to provide a fairly large potting mix surface for this fern as it is a quick grower under good conditions.
Lygodium japonicum Climbing Fern; 7°C/45°F mm; Japan
The petiole and rachis are very long and wiry, climbing by twining round a trellis or pillar. Oppositely paired pinnae grow out from the rachis and are yellow-green to medium green in colour. Fertile pinnae are long and tapering with serrated edges, the lobes of which carry the sori; sterile pinnae are similar in form but with more and deeper serrations. When grown on a windowsill, a climbing fern is liable to twine through light curtains or Venetian blinds unless precautions are taken.
Nephrolepis 10°C/50°F min; tropics and sub-tropics
N. cordifolia (Sword Fern) Very short petioles carry long narrow blades cut to the rachis, forming segments, the whole frond growing to a length of 60cm/2ft. The colour is light green. Large plants are best grown in hanging baskets or on pedestals, for the mixed upright and pendulous fronds show to advantage from a low angle. In the cultivar ‘Plumosa’ all the segment tips are fringed. N. exaltata (Ladder Fern) Very similar to N. cordifolia but much larger and coarser, with pale green fronds growing up to 2m/6^ft long. The blade tapers at base and tip and looks somewhat like a ladder in silhouette. Many cultivars of N. exaltata have been produced by crossbreeding; most are of interest to indoor growers, the greatly divided blades giving cristate forms. N. exaltata ‘Bostoniensis’ (Boston Fern), with broad fronds and fast-growing, was a very early mutant and the many later mutations have provided us with modern cultivars that are easier to grow in present day living rooms. ‘Rooseveltii Plumosa’ has very wavy segments; ‘Whitmanii’ is commonly called the Lace Fern, a description in itself; ‘Elegantissima’ is similar to ‘Whitmanii’ but more upright. Occasionally a frond will revert to the original single segment form and it should be removed immediately. Often spores from these cultivars are infertile and then the form can only be propagated by runners.
Nephrolepis are propagated by runners growing from the top of a rhizome; the runners root quickly when in contact with moist potting mix.
Pellaea 7°C/45°F min; New Zealand
P. rotundifolia (Cliff-Brake or Button Fern) Brown hairy scales cover a wiry petiole and rachis which has about 20 pairs of alternately placed pinnae. The small roundish pinnae are dark green above, light green below and a little leathery. Fronds up to 50cm/§ft long form a low spreading mat so that this fern is useful in
temporary plantas ground cover for it is fairly tolerant as to conditions and able to utilize any humidity from surrounding potting mix. Sori form on the underside margins of a pinna but do not meet at the apex and are light brown in colour.
P. viridis Unlike the previous fern this African species is upright and bushy, has fronds growing up to 75cm/22ft long; rachises are green when young turning shining black with age and blades of bright green spear-shaped pinnae. It is unusual for a fern to grow well in very bright light, but this species does well under the lower intensity of fluorescent lighting. It also needs a minimum winter temperature of 10°C/50°F.
Platycerium biforcatum Syn. P. alcicorne; Stag Horn Fern; 10CC/50°F min; Australia
True epiphytes in that they grow on trees without taking food from them, the Stag Horn ferns are unlike any other ferns in appearance. There is no mistaking sterile for fertile fronds. The former are wavy-edged, fan-shaped, pale green in colour and grow out from a very short rhizome. With age they enlarge and in nature grip a tree trunk or branch making a firm anchor for the fern, growing frond over frond so that the originals rot to provide food at the roots. The fertile fronds emerge from the centre and are antler-shaped, the older fern having more and larger ‘tines’. These fronds are a darker green but appear greyish-green because they are covered by fine white hairs like velvet which are very easily removed by barely touching them. Sori form large brown patches on the underside of the antler tips. In the home a Stag Horn may be grown in a pot or attached to bark padded with sphagnum moss; either way, in time sterile fronds will cover the holder. It should be watered by immersing pot or bark periodically, preferably in rainwater. To keep its beautiful velvety appearance, inquisitive fingers should not be allowed to touch the fronds as once removed the ‘velvet’ will never return.
Polypodium aureum Syn.aureum; Hare’s- or Rabbit’s-foot Fern; 7°C/45°F mm; West Indies
Good specimens will grow fronds lm/3Jft tall, although young plants of 40cm/16in are very decorative. The frond has a light green petiole turning brown with age, a blue- to yellow-green blade made of single and opposite pinnae each up to 12cm/5in long. In some cultivars the pinnae have wavy edges. Each frond arises
from a thick silver to brown furry rhizome that gives this fern its common name. The rhizome is surface-creeping and will follow the contour of a. Dead fronds drop away leaving a scar on the rhizome rather like a small footprint.
Pteris 10-13°C/50-55°F min; Meditcrranean/Tropical Asia
P. cretica (Ribbon Fern) A very short rhizome is common to all Pteris so that growth is in clumps with very many fronds arising from a crown. P. cretica, about 50cm/lfft tall, has longish pointed pinnae with serrated edges that only show on the sterile pinnae because the sori are protected by the pinna edge curling back. It is medium green in colour and quite tough.
There are many cultivars, all more interesting in shape or colour. P. c. ‘Albolineata’,
as the name implies, has a white central line running the length of each pinna; ‘River-toniana’ has pinnae with elongated segments growing irregularly from the margins; ‘Wil-sonii’ and ‘Wimsettii’ both have heavily crested tips to their pinnae.
P. ensiformis The cultivar P. e. ‘Victoriae’ is grown much more often than the type. It is a most attractive plant with short bushy sterile fronds having pinnae with white central veins banded by dark green serrated margins. Fertile fronds are taller, up to 50cm/l§ft, with very
slender long pinnae on which the serrations only show at the tip, where the margins stop curling back over the sori.
P. tremula (Trembling Fern) This quickly-growing fern can reach over lm/3ft if given the opportunity. However, young plants of 30-40cm/12-16in are useful forwith other pteris species, the yellow-green foliage making a perfect foil for the darker greens. The feathery blade is triangular when seen in silhouette, and the pinnae have very deeply cut serrations.