PROPAGATING FERNS FROM SPORES
Many local ferns are suitable for the woodland rock garden and propagating them in small numbers is easy if you have a bright, warm spot inside during the winter (fluorescent light or a bright windowsill without direct sun is ideal). If spores are sown in the fall, most plants will be ready for the garden the following summer. Below I describe how I grow small numbers of local ferns. They are all common and distinctive enough to be recognized with a field guide.
Step 1: Collect spores
You need only a very small amount. The spores from a few leaflets (pinnae) of 1 frond will be sufficient and the plant does not need to be harmed or disfigured. Check the underside of the fronds. Some genera such as Osmunda have separate fertile fronds. Always get permission if you are not collecting on your own property.
The sori (round or oval structures containing the spores) will usually be brown or black when ripe. Keep the pinnae in a plastic bag until you get home.
Collect in June :
Collect in August-September:
Step 2: Dry the spores
Allow the pinnae to dry between a piece of white or wax paper for 1-2 days. If the spores are ripe there should be a fine dust on the paper.
Step 3: Sow the spores
Spores are best sown fresh but can be stored for a short time dry in the fridge. Use a clean, 4 inch pot filled with soilless mix. Place a square of newspaper over top and pour boiling water slowly over the pot to partly sterilize. After the pot has cooled, gently tap the spores from the paper onto the surface of the mix - you only need a pinch thinly scattered. Put the pot in a resealable plastic bag and place under bright light. If you are sowing more than one species be careful to wash all instruments and hands in between.
Step 4: Waiting
In 2-8 weeks the surface of the mix should start to turn green and small, flat prothallia will be visible.
A light misting at this stage will encourage fertilization. After another few weeks or months the first few fronds will appear. The timing varies with species. I have found Dryopteris and Adiantum grow quickly whereas Polypodium take a long time. If nothing happens after a couple of months, put the pot in the fridge for 4-8 weeks.
Step 5: Potting
When the young plants are 1-2 inches tall with a few small fronds separate them and plant in small pots. Protect the roots from drying during this time (misting helps). Return the pots to a plastic bag and keep in high humidity until growing again. Since homes are dry during the winter open the bag gradually over 2-3 weeks and keep the medium moist. In spring harden off with other seedlings and plant out in a suitable location. Don't let the young plants dry out until established.