I've heard of sticking the end of the runner in a pot to root and later cutting it free, but I would think baggie wouldn't drain, and zipped shut would just make it rot (condensation)?

Actually, it probably would work - I would poke a couple of drainage holes on the underside, and make sure to keep it moist.

I wouldn't stick the plant down in the bag, I envision it more as the bag full of media is laid horizontally on the ground, an "X" shaped opening is cut in the plastic, the root initials of runner stuffed into the slit with the crown just above the plastic and leaves above in the light and air. Basically kind of horizontal air-layering.

Yeah, if holes in the bottom for drainage and leaves sticking out (whether top not zipped or bag laid on its side and X cut for plant) that would work. Like a pot but cheaper - as long as you can get it to drain well. Might be easier to use something like disposable foil "cupcake" or individual cake pans they sell around the holidays. poke a few holes in the bottom and they're a little more rigid than baggies so when it's time to cut the "apron strings" and move the runners they'll be easier to pick up.

I think I'll try it. My plants are throwing runners now.

I've read about the way commercial growers propagate tips cut off the runners. It apparently takes regular misting to keep them moist. The baggie idea would seem to come close.

Strawberries are pretty determined to grow.

Last year I just let the runner root for a little while, then pulled up the plantlet, sometimes carefully, sometimes not and moved a whole set to a few new rows. Seemed to work fine, though the distance I was moving them was only a couple of feet. So I did it without a baggie or a pot.

I did the same as sunnibel last year. This year I need to move them a lot (DH said he'd level and prep the other half of the stone wall), may sell some too so I just figured I'd set pots in the bed and let them root right in the pots. Maybe I'll try a few baggies for the ones I'm going to keep (if DH gets the hill dug out a little so I can plant them right away - I don't know how long I'd keep the baggies).