Growing Ferns From Spore
(courtesy of Sue Olsen)
Ferns are reproduced from spores that are gathered in clusters called sori, which are usually on the underside of the fronds. The spores can be yellow, green, brown, or black. The sori are sometimes covered with a membrane called an indusium, which will lift up when the spores are ripe. In the Pacific Northwest, spores ripen from late May through October and will waft off like fine dust.
To gather the spores, pick a frond or portion of a frond and place it between two sheets of white paper. If ripe, the spores should drop within 24 hours and will leave a pattern on the paper. Frequently, chaff will drop as well, and this must be removed before sowing. To get rid of the chaff, tilt the paper slightly and tap gently. The chaff will fall away while the spores remain behind. (Practice with a non-important fern first!!)
The spores are then ready to be sown. I use a clear plastic container with a sterilized earthworm compost mix, but there are many other options. The spores are dusted on the top of the mix and the lid put on the container, which is then placed under cool white fluorescent lights that are turned on for 14 hours a day. The spores must be out of direct sunlight.
In time perhaps as soon as several weeks a thin, green haze will form on the mix. This will grow into a carpet of prothallia, which are small, green, heart-shaped structures and contain the sperm and the egg. When the prothallia are approximately ¼ inch, they should be lightly misted to hasten fertilization. If no little sporelings appear in several weeks, mist again.
I then move small clumps of prothallia/sporelings to a mix of peat,
vermiculite, and compost potting soil in a covered mini-greenhouse.
This is also placed under fluorescent lighting where the sporelings are
grown on until they are about one inch tall. At that time I harden them
off by gradually lifting the lid of the greenhouse. They are then
transplanted into pots, and finally moved out of doors when they are
four to six inches tall depending, of course, on the season.
Prothalli with the first true frond coming up on the right.