In late summer to early fall many ferns produce spores, and you can propagate hundreds of new plants with just a few spores. To uncover fertile ferns, inspect the underside of various fronds for bunches of dark brown, pimplelike clusters of spore-bearing sacks. Cut the frond at its base, place the frond spore-side down on a sheet of white paper, cover it with another sheet of paper, and place a paperweight on top for a couple of days.
Growing ferns from spores requires extremely sterile conditions, so make sure that the container in which the ferns will be planted is cleaned well with a solution of bleach and water. Once it's clean, fill the container with about an inch of perlite, followed by two inches of peat moss. Moisten the mix with boiling water and cover the container.
A day or two later, remove the paperweight and the top sheet, and you should see a fine dust of spores on the bottom sheet. Crease the paper carefully, and transfer the spores to the potting mix, spreading them evenly, and replace the lid. Place the container on a north-facing windowsill or under lights, but don't expose it to direct sunlight. Within a month, you should begin to see a pale green film growing over the potting mix. A few months after that, miniature ferns should begin to develop. You may have to mist occasionally to keep the mix moist, but remember to use distilled or boiled water to avoid contamination of any kind. As new fronds appear, transplant the ferns into another sterile box containing a rich potting mix (such as that made for African violets). Once the ferns are two inches tall, they may be transplanted to the garden, assuming all danger of frost has passed.
