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Garden Blog

Fall is Fern Reproduction Time!

By Heidi Koonz, KBGF Staff Horticulturist

It’s getting to that time of year where many gardeners are itching to ‘work’ in their gardens again.  Ordering seed catalogs, planning for fall planting, etc. are enough to keep the leagues of the green thumbed ones happy in the interim.  But what about trying your hand at something new?  Have you looked at any of your ferns lately?  If you have, and checked on the underside of their fronds (= to a fern’s leaf), you may have noticed some small raised bumps in interesting arrangements.  These are called sori, and house the many small dust –like spores that are the ferns reproductive structures.

Unlike our flowering plants that make seeds, ferns are prehistoric plants, and their methods of reproducing are more primitive.  Spores can produce a plethora of offspring if the conditions are ideal for their germination.  But unlike seeds, spores require very specific circumstances to begin their life cycle.  Although this may sound off putting for the average gardener to want to dabble in, fern propagation can be a fun and rewarding way to expand you horticultural skills.  It requires minimal supplies, but attention to detail is important.

First you need to be able to acquire spores.  Since many spores ripen in late summer, this is a good time to be checking the back sides of your fern fronds.  When they are ripe, they generally look plump, and raised up.  If the sori have already shed their spore, they will appear flat and dark.  Collect and label your specimens, and keep in an envelope or paper bag that you seal.  Leave in a warm, dry place for them to shed.  Once the sori have released their spores, you need to separate the chaff from the spore, and you can store it for sowing later, or if you’re ready, so it at this stage.  Ferns need a sterile medium to germinate in, and constant moisture.  A clean and clear container that has a lid you can seal work best for this.  Once the container and medium are prepared, the spores are sown, and you wait for the ‘magic’ to happen.  After a few weeks, a green carpet (prothalii) may appear to have taken over the soil.  This is the first stage of germination, and needs to stay moist, covered, and in bright, direct light for 10 + hours a day.  A couple of months after the spores have been sown, you should begin to see the emergence of tiny fronds from the young prothalii.  Now, you have successfully grown a fern!  Be very careful when they are big enough to transplant to a larger container, they desiccate very easily.  Keep them moist, but not wet.

For more detailed information on fern propagation, check out KBGF horticulturist Heidi Koonz's article in the fall edition of the Washington Native Plant Society’s quarterly journal “Douglasia”.