Sowing fern spores - part 2

Half term is a time for many jobs, so although I'd hoped to do the actual sowing yesterday I just ran out of time. Today I've painted some garden furniture, been to the bank and also spent the afternoon digging over / building up a bed on the allotment. At last, this evening, I've some time for my ferns again. 

The spores are supplied wrapped in aluminium foil and when the packet is opened it looks like there's hardly anything there! All you see is a little bit of dust. Most of the spores I was sowing were Dryopteris spp. which all have dark spores, but I also had some Ophioglossum vulgatum which were a pale yellow. 

In this photo (pencil and tweezers for scale) you can just see the brown dust of the spores on the foil. The spores are single cells, so very very small. It's a miracle of nature that it works at all; when you think about it, most reproduction seems quite chancy, but it clearly works!

There are several recommended methods for transferring the spores onto the growing medium. I mostly tapped mine out, but I sometimes used a knife blade to lift them and tap them out as the small size of the spores means they easily become stuck to the foil - which might be static,  or might be capillary action/microstructure of the cell surfaces. Tapping out increases the risk of raising spores into the air and cross-contaminating between species, but I was careful to keep the plastic over the spores and to avoid sudden movements that could result in large air currents. I removed and discarded the paper towel and tapped the spores onto the surface of the growing medium. When I used a knife I was careful to clean it with isopropyl alcohol between sowing spores of different species. 

After sowing, I re-sealed the pots in their plastic bags. Labelling is crucial if you want to be sure what you've grown. I had 3D-printed some labels in advance - they were designed in SCAD and I added a pause point to the g-code so that I could swap out white for black when the lettering began to be printed. I might yet get round to uploading the design to Thingiverse if I can be bothered to tidy up my code a bit. 

I then placed all my pots on a north-facing window sill (the heating is now off for the summer, so they should be in no danger of over-heating).  

Over the coming weeks (from a fortnight to several months) I'll be looking for a green film to appear. Over time this should turn into a host of prothalli, the gametophyte generation. Sexual reproduction should then occur between the prothalli and new sporophytes (the stage we recognise as ferns) should begin. At least that's what should happen if it all works ...

I'll post some updates when I spot any changes. 

Sowing fern spores - part 1

 It has been a long time since I last grew ferns from spores, so I thought I would try to capture the process here, along with some tips and observations about how it works and some advice for others who would like to give it a try, 

The first step is obviously to obtain some fern spores. You can do this directly from plants when the spores are being released, but one of the many benefits of being a member of the British Pteridological Society is that they operate a spore exchange scheme. So I'm beginning this time armed with some spores I received earlier in the year. Ideally, one would start a little earlier in the year, but being a teacher it's only now that study leave has begun that I've found some time. 

The big difficulty with growing ferns from spores is that they need to be kept permanently warm and wet: that's an environment where many other things thrive, especially mould. To counteract that, the sowing medium needs to be sterilised. 

In my previous attempts to grow ferns from spores, I've done so with compost, but this time I've decided to try out a different growing medium. I started by making a mixture of 1:1:1 coconut coir, vermiculite and perlite. 

The vermiculite I've used here should properly be called exfoliated vermiculite, as it is produced by heating vermiculite clay so that it has changed its structure and expanded. It promotes good root growth and allows the passage of air into the growing medium.

Perlite is also a processed rock substance, in this case a volcanic glass with a relatively high water content, which is heated so that it expands. Non-toxic and large-grained it works in a similar way to perlite.

I prepared my mixture outside as vermiculite and perlite both contain silica and it's best to avoid silica dusts. I aimed to make 3L of mixture and added about 1.5 L of hot water from the tap to enable the coir to expand. I then packed the mixture into twenty 3" pots as I have 10 species to sow and want to do two pots per species. 

I cut circles of kitchen paper to fit on the top. This protects the mixture (to an extent) in the next step and provides a layer that can be removed when sowing ensuring a fresh surface.

I next set about sterilising the growing medium using boiling water. Complete sterilisation and sterile techniques are not needed (it's not bacterial culture on agar) but pouring boiling water through the pots will sterilise the top 1-2 cm, which will be enough to let the ferns get established. I sterilised them in batches of five, monitoring the temperature of the water that passed right through. With a 1.7 L kettle of boiling water, the temperature at the bottom of the pots was 70 deg C. 

As far as possible, it's best to pour slowly so that you don't end up with too much disturbance of the surface. Some indent into the surface is inevitable from the impulse of the falling water, but if enough water is added, the top layer often lifts and floats, re-levelling itself. The pot top left is the best one here, while the one bottom right has been less successful (but will still be ok). 

Already, I'm liking the growing medium better than the compost: when boiling water is passed through compost it can be quite smelly - with strong earthy odours, whereas the smell from this is almost non-existent. Earthy smells (sometimes referred to as petrichor) are caused by two main chemicals - geosmin

and 2-methylisoborneol

However, I digress, as at this point it's important to act quickly before too many mould spores fall out of the air. I used plastic food bags to cover the pots. Scalding is a real risk at this point - watch out for drips! Some people recommend using ceramic rather than plastic pots as plastic doesn't cope well with heat. However, providing reasonably sturdy pots are chosen (these are Stewart premium pots from my local garden centre) then they don't deform in this process. There is a slight plastic aroma and it's likely that the hot water heats the plastic enough for it to lose some of its plasticiser, so it's best to work in a well ventilated space and I wouldn't recommend growing food crops by this method as there is a risk of leaching into the growing medium). 

I then secured the bags with rubber bands below the rims of the pots, cutting off the excess and sealing the remainder of the bag with a kitchen clip. 

 

 

The pots are now ready for sowing, but need to cool completely, so sowing the spores will be a job for tomorrow. I've stood mine in narrow trays as they will need to sit on a north-facing window sill.