I lose about half of my strep leaves when I propagate by leaf cuttings. About half turn brown (rot)fairly quickly. I am using 50% perlite/50% vermiculite. The leaves are cut along the midrib.
Propagation of Strep leaves is tricky at the best but more so when the mid rib is removed. I have had better success by cutting leaves horizontally with the mid rib intact and planting several pieces of horizontal sections. Then, it is very important to make sure the propagation mix is just slightly moist (damp is the operative word here). Too wet a propagating mix is the major cause for loss of Strep leaves.
Hope this helps.
I find the use of sphagnum moss, either milled or long-fiber depending on what I can find, helps a great deal; I've heard there is a natural fungicide in sphagnum that helps prevent various problems such as damp-off and rots. Especially with the milled, I mix vermiculite about 50/50.
I agree with both above. I only use moss when I really want to make sure I save a weakened cutting. Moss works very well, but if I leave the cutting it knits its roots so well into the moss that it can be hard to remove the moss when planting on. Though, I don't think this is really that much of a problem (leaving the moss around the base of the rooted plant).
I describe the method Marilyn uses as a wedge cutting. I cut across the leaf, so that the midrib is in the center of the cutting. I shape it between the side ribs so that the cuttings are arrowhead shaped (hence wedge shaped). Each cutting can be as short as 2 inches or as long as six inches, mol. Perlite/vermiculite works really well, as long as it is not tamped down, which happens when it is watered too heavily. Wet it thoroughly then fluff it up, put it back into the pot and plant the cuttings. Putting the small pots under a community dome works best, along with a clear topped plastic box (aka "sweater box"). Putting the pots in individual ziplock plastic bags works almost as well, though rot can happen more often.
The most important thing, after all of this, is to put the container with the pots in good even bright light. The best place to root streps and other gesneriads is under lights on a light stand. The next best place is a bright window without direct sun. In lower light the cuttings will rot. And, I never had much luck with the long leaf cuttings with midrib removed. I also have much better luck when I take healthy leaves from plants that aren't in decline. But, even completely wilted leaves from plants with crown rot will root (first cut the leaf off and soak in a bowl of water for up to 24 hours to return to turgid conditions, then plant). Make sure to cut well back from any signs of crown rot, which can look like dark maroon discoloration of the midrib.
Streps root best if not kept too warm. They love moderate temperatures that tend to be on the cool side of human comfort, but generally do fine in the same range as AV's.
Jon--hope this helps.
In the interest of 'truth in advertising', I should correct myself above--I use perlite, not vermiculite. Not sure vermiculite wouldn't work just as well, at least if you pot them on in a more timely fashion than I do sometimes, but what I actually do use is perlite. I like an airy mix!