Propagating ferns

Last time I wrote about propagating ferns from spores, I neglected to take photos until after the spores had already begun to germinate. Last August 10th, I sowed a few fern spores again and that time I remembered to take photos. However, I wanted to wait for the spores to germinate and start to look like something before I wrote this post. That's right. This post has been a full year in the making.

Follow the link above if you want to read about some of the more geeky details of fern reproduction. This post will focus on the materials and methods I used to propagate ferns from spores. In this round, I sowed spores of Cyathea dealbata and Dicksonia squarrosa collected at Cistus Nursery, and Blechnum gibbum spores from my own plant.

A year in the making, and I still manage to not include photos of everything I should. Collecting the spores obviously comes first, but I have no photos of that to show you. Sporangia (the structures on the underside of a fern leaf) come in many shapes and sizes, but generally if you can see black or brown specks in the sporangia, the spores are mature and ready to be collected.

Here are a couple examples of sporangia:

Immature sporangia on Asplenium x kenzoi. See the tan-colored lines? Those will split open along one side when the spores are mature. At least, assuming this hybrid fern produces viable spores, but sterility of fern hybrids is another topic.

Sporangia on native sword fern, Polystichum munitum, are open, bearing their golden brown spores on little domes in two rows along the underside of each leaflet. 

Once you've determined your fern spores are ready to collect, you simply cut the frond off and press it between two pieces of cardboard, or simply place the fronds in an envelope, to dry. This usually helps the sporangia to release their spores. Some ferns have a bit more trouble letting go. Once the fronds have dried, you can shake up the envelope a bit and you should see a pile of black or brown dust in the bottom. Those are the spores! If the spores haven't been released, you'll have to shake the envelope a bit more aggressively, or even crumble the fronds in your fingers. The latter is a bit of a problem as it leaves bits of fern frond in with the spores, which can encourage mold.

With spores ready to sow, I gathered my materials.

Something to boil water in. I used an electric kettle because it's faster than boiling water on the stove.

Containers to sow the spores in. I like using these plastic salad containers. It's actually best to remove the labels, which I did belatedly after writing the names of the ferns on them and taking this photo. The label creates a shadow area that will reduce or prevent germination in the center of the container.

Spores and soil! The crispy fronds in the photo on the left are the dried fertile fronds of Blechnum gibbum. They did not release their spores very well. so I had to crumble them up. They may not have been ready, as I didn't get any germination, or I may have left them to dry too long. Spore lifespans vary widely. Some fern spores will germinate months after collecting and drying. Others last a few days, so drying isn't really possible and I'm not sure how to handle those types. The photo on the right is a mix of a bark-based potting soil and peat moss. Peat moss lowers the pH and helps to reduce fungal issues in the humid environment the spores require. Most ferns germinate well on soft, decomposing chunks of wood, like one finds in a forest or woodland, so look for a chunky potting soil.


Materials gathered and water boiled. Now I pour the water into the pot of soil in the photo above. This sterilizes the soil to reduce the chance of fungal or bacterial outbreaks. It should be fully saturated with boiling water. I had to boil a second pot to fully saturate the amount of soil I had. I then placed a plastic bag over the container to prevent seeds or other spores floating in the air from landing on the sterilized soil. Then find something else to do while the soil cools. It can take awhile....Seriously, you should probably go pull some weeds or something...

Once the soil has cooled sufficiently to work with, fill each salad container with a layer of soil about 2 inches deep. Then sprinkle in the spores. You can see in the photo below the bits of leaf scattered among the spores. I tried to pick as many of those out as possible to reduce the risk of mold.

Then close up the containers and put them somewhere with bright light, but protect them from direct sunlight and avoid temperature extremes. I kept mine indoors under fluorescent lights, not strong enough to turn the mini greenhouses into ovens, in a room that stays in the mid-70's Fahrenheit in summer and 60's in winter. Don't worry about drainage holes. These will be sealed up for months and won't need any additional water. Just check occasionally for mold. If you do find mold, remove the affected area and keep the lid open a crack to let it dry out a little. If the soil starts to look dry, use a spray bottle to thoroughly wet the soil, but not enough that you can see water flowing in the bottom of the container. When you start to see little filmy green, often heart-shaped structures growing on the soil, your ferns have germinated! But those are the gametophytes. Fern hanky panky will occur at some point ( an occasional misting helps the mood) and from those gametophytes will grow the fern plants we're familiar with.

As I've said before, growing ferns from spores takes patience. I sowed these spores last August. In this post, you can see what they looked like in April of this year. When you see fronds starting to grow out of the gametophytes, you can start occasionally misting with a weak fertilizer solution, no more than 1/4 strength. I found recommendations for using fish fertilizer, and anecdotally I would say it greatly improved the growth of the baby ferns. You can see their current status below, one year after sowing. They are starting to look like ferns! (Did I mention that growing ferns from spores is only for the very patient?)
I had excellent germination of the Cyathea dealbata spores, plus lots of moss and a few mystery ferns. 

Closer view of the Cyathea dealbata fern babies.

Only three Dicksonia squarrosa, but the two larger ones are growing gratifyingly fast (for baby ferns, that is). I had hoped to get enough germination that I could return a whole crops worth to Cistus Nursery, where I collected the spores. Hopefully the current propagators will have better luck. 
 Just enough Dicksonia squarrosa for me. At least I'll be able to give them lots of Cyathea dealbata, provided I can keep them alive through the tricky step of transplanting them to individual pots. I've been taking steps to prepare for that. The problem is that the young ferns go from a very high humidity environment (the salad containers) to open air. The leaves are very thin from the high humidity environment, drying out easily out in the open. I've been gradually opening the lids of the containers more and more to acclimate them to lower humidity. Baby ferns also resent disturbance. Not much I can do about that. The two biggest Dicksonia squarrosa are probably big enough to move to a normal pot with drainage holes, but I'll wait until fall when the air is cooler and more humid. Hopefully the Cyathea dealbata will also be large enough to transplant by then.

And while we're on the topic of growing ferns from spores, here are the Cyathea dregei I've been growing for 2 years (or more, as I mention in the "Caught Green-Handed" post).

Some of them are still quite small.

But at least half of them are actually big enough now that I could pass them on to Cistus, as I intended. I do plan on keeping a couple for myself, of course.

Comments

  1. Incredible. How is it that ferns aren't more expensive with all the time and effort it takes to raise them from spores? Thanks for the morning laugh (fern hanky panky...misting helps the mood.)

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    1. Well, ferns produce a lot of spores, making it easy to propagate large quantities of most species. Not all of them are as slow as these tree ferns, and I imagine with the right conditions even the ferns I'm trying to grow are much faster. My Pteris wallichiana were much faster, growing to garden-ready size in less than 2 years, and that was with the shock of moving across the country and a poorly-executed transfer to individual pots. Glad to provide a morning laugh!

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  2. Astonishing. I hardly have enough patience when I plant bulbs in the fall to wait till spring... You are 2 years into it, and I'd say you have tons of patience. Very cool to read about fern hanky panky.

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    1. To be fair, Cyathea dregei are especially slow and I don't have the facilities or experience to really make them grow at full speed.

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  3. A major production! But if adult ferns had a better survival rate here, I'd give it a try.

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    1. Hehe! That doesn't stop me from growing tree ferns! I can't grow mature specimens of those outside without protection, and winters like the most recent one would probably wipe them out even with protection.

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  4. Terribly fabulous, thanks for tracking the process for so long. Your dedication is admirable and I know that boiling water tip is going to come in handy someday.

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    1. Thanks, Loree! Sterilizing the soil with boiling water is also a trick used when you have really special seeds you don't want to risk losing to fungus, and some seeds actually germinate better after having boiling water poured over them. Sophora davidii and other legumes are good examples.

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  5. Great post! Gives me some confidence that I might end up with more ferns. I recently embarked on this same process, am at spores sprinkled on sterilized compost stage. Months before I see anything, probably.

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    1. Thank you, and thanks for reading! Good luck with your spores! Have patience.

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