spores.page

(4) Conditions for Germination

     For spore to germinate, it must be kept moist at all times. This is simply achieved by placing sown pots in a closed container (e.g. plastic ice-cream container, food crisper or glass aquarium covered with a sheet of glass). Provided there is reasonably close contact between the top of the container and the glass cover, the pots should remain moist almost indefinitely. The pots should be sufficiently moist from the sterilization process and do not need to be standing in water (although some growers advise it). Pots should not be watered from above in the early stages or the spore will be washed away.

     Germination seems to occur most rapidly if the spore receives a fair amount of light. A north or east facing window generally provides a suitable aspect, providing that direct sunlight does not fall on the pots. A single thickness of white rubbish-bin liner is often sufficient to diffuse sunlight.

     Germination is usually apparent within 3-4 weeks as a fine green film across the surface of the pot. Each tiny green speck slowly develops into a flat, heart-shaped prothallus (the first stage in the life cycle of the fern), usually 2-5 mm across. The prothalli may begin to produce true fronds from the notch of the heart at almost any time from 2-3 months in some very rapid species to several years in other cases. Once prothalli are a reasonable size, any growth of fungus or mould can usually be checked by gently watering pots with half strength Benlate solution.

(5) Pricking Out and Potting On

     The tiny sporelings may be pricked out into tubes or trays with only one or two true fronds developed. Containers should be filled with a suitable potting mix and thoroughly moistened. A mixture of about 2 parts peat moss, 2 parts washed river sand and 1 part mountain soil, all ingredients having been sieved, (or any standard propagating mix) should prove satisfactory.

     By carefully grasping a tiny frond between thumb and index finger, it should be possible to lift the fern off the pot with its prothallus still attached. At this stage, true roots will usually not be well developed, and the prothallus can be gently pushed down onto the surface of the new pot or tray to support the tiny fern plant. This should be done fairly quickly and in a cool, draught-free location as the delicate sporelings will not survive for long out of the humid atmosphere they are used to. As soon as possible, transplanted sporelings should be very gently watered and placed under glass again.

     If the sporelings are allowed to grow too large and crowded before they are pricked out, they may be scooped out in clumps with a spoon, placed in a saucer of water, and then gently separated and planted into tubes or trays. Again they should be replaced under glass without delay.

     The newly transplanted sporelings should be allowed to develop under glass until their fronds are about 5-10 cm high. At this stage they may be very gradually acclimatized by slowly raising the glass cover, a few millimetres at a time, over a period of 4-6 weeks. You will need to keep a close watch at this stage to ensure pots don’t dry out and you may need to water some plants from time to time. Ferns in trays may be potted up into tubes or small pots either before or after this hardening off process.

     If you wish to plant these ferns in an outdoor fernery, they are best grown on in a cold glasshouse until fronds reach about 20-30 cm and then planted out, preferably in mid-spring, when indoor and outdoor temperatures are very similar.

     Using the techniques outlined above, it is not unusual to grow one or two hundred ferns from each 5-6 cm pot sown with spore.

You might also be interested to read about how I grew
Cyathea marcescens (a naturally occurring hybrid treefern)
from spore.

     You might find the above techniques just a little daunting .... after all ferns manage to propagate themselves in the wild without all this fuss, so there must be an easier way!

PROPAGATION OF FERNS FROM SPORE

(1) Collection of Fern Spore

     Fern spore usually develops on the backs of fronds in special structures called sori. Each sorus is made up of a cluster of roughly spherical sporangia, each sporangium containing a large number of spores (64 in most species). Sometimes the sorus is protected by a membrane called the indusium. The shape of the sorus and indusium varies considerably for different ferns.

     It is most important when collecting fern spore to be able to judge when the spore is ripe, and this may usually be accomplished by careful observation. The sporangia are initially light green and slowly ripen, often to dark brown or black, at which time they appear swollen and shiny. As the sporangia then burst and release the ripe spore, the sorus takes on a rather tatty or furry appearance.

     Often you will be able to see all stages of this development on a single plant, if not on a single frond, and you should collect sections of frond in the region where the spore is ripest, just before the tatty area where spore has been shed.

     In cases where the sorus is covered by an indusium, this may lift or shrivel as the spore ripens (e.g. Lastreopsis, Rumohra, Polystichum, etc.,) but if not (as with some Adiantums and Aspleniums) you may need to peel back the indusium and examine beneath it with a small hand lens (x10 magnification) to check for ripe sporangia.

     Some spore ripens to yellow (e.g. Davallia, Dicksonia, Gleichenia, Sticherus, Microsorum). Most members of the Osmunda family (e.g. Todea and Leptopteris) ripen to dark green, the empty sporangia being yellowish to brown.

The sections of frond collected should be loosely arranged, with sori facing down, on sheets of clean paper. These should be kept in a warm dry spot, away from draughts, and allowed to dry out for a day or two. If the spore is ripe, very fine powder should start to collect on the paper within a couple of hours. If you are not sure whether spore is ripe or not, a very small piece of frond may be tried first (as with this pinna of Christella dentata at right).

   When the fronds are dry, gentle tapping will dislodge any trapped spore. As well as the very fine spore, you may also collect a quantity of the coarser sporangia husks. These may be separated fairly simply by holding the sheet of paper on an incline and repeatedly tapping the paper sharply. With practice, you should be able to make the husks slide away down the paper, leaving the spore behind.

     The spore may then be swept with a soft brush, or tapped down a fold in the paper, into a small paper envelope (ensuring corners are sealed with tape) for storage. Packets of spore should be labelled with the name of the fern and the date of collection, and kept in a cool, dry place until needed. Although it is generally recommended that spore be sown fairly fresh, in many cases, spore kept in an airtight container with a packet of silica gel should retain its viability for several years.

(2) Preparing a Suitable Medium

     Any fairly coarse, porous material seems to be suitable. Very old, well decomposed, shredded Soft Treefern fibre gives excellent results if available. Peatmoss (unsieved), crushed terra-cotta pots, charcoal or Elkhorn fibre (or combinations of these) have also been used successfully. Another alternative is a mixture of equal parts coarse sand and treefern fibre (or peatmoss) and I have even seen a good crop of healthy ferns growing on an ordinary kitchen sponge.

     I have found 5 or 6 cm square pots quite sufficient to grow a fairly large number of ferns, enabling a few different species to be raised in a relatively small space. The pots may be filled with the chosen medium or a 2-3 cm layer may be added on top of your normal potting mix. This may be sterilized by carefully pouring hot water (see below) through the mix and then standing the pots in hot water, up to the rim, in a closed container, for an hour or so. The pots should then be removed, hot water poured through the mix for a second time and then allowed to cool, again in the closed container. If the mix contains no organic material then boiling water may be used. However if organic materials are present, the water should be boiled but then left to stand for 5-10 minutes before it is used. Boiling water often releases toxic chemicals from organic materials, resulting in poor germination and growth.

     If a finer medium is used, sterilization with boiling water may prove rather messy. In this case, the mix may be placed in a tray, covered with foil to retain the moisture, and baked in the oven at 250 F for about an hour and a half.

     Sterilization is necessary to kill off any moss or fungus spore, or unwanted fern spore, which might be present in the mix.

(3) Sowing the Spore

Probably most failures will come from sowing spore too thickly. One way of sowing spore thinly is by covering the end 1 cm of a small clean penknife blade (or very small chemical spatula, as shown at right) with the spore and then gently tapping off the excess to leave only a thin single layer of spore adhering to the blade. This is quite sufficient to sow a 5-6 cm pot. To sow the spore, hold the blade 6-7 cm above the pot and give it a sharp tap with a pencil to dislodge the spore. This must be done in a perfectly still room, completely free from any draughts or breezes.

Treefern logs, especially Dicksonia antarctica, are a favourite place for spores to germinate in my fernery, especially the vertical surfaces where dead leaves cannot settle and smother the developing prothalli. Lots of spores settle there from ferns growing nearby, but I also place sections of ripe fronds on the logs to grow some of the more desirable species. Of course the logs must be kept constantly moist. Sporelings need to be potted on when very small (one or two true fronds) or they may be difficult to separate from the log and each other. The big advantage then is that they are already hardened off.

Another favourite spot is in an undercover fernery with a fibre-glass roof. I have used a mulch here of 3-4 cm of granite chips (~1 cm diam) on top of very ordinary sandy loam. A sprinkler system keeps it fairly moist and fern spore germinates here quite freely, as well as in the cracks and crevices of the basalt rocks in this same garden.