Did you know that propagating a Watermelon Peperomia (Peperomia argyreia) by a leaf cutting is the most simple and efficient way to multiply your plant? Here, I'll show you the exact steps I took to propagate mine and answer a few of the questions I've gotten along the way.
Making the leaf cuttings
Start by choosing healthy leaves for your propagation. You can use the dying ones but the chances of them actually growing roots will be much lower. Simply snap off the red stem and make a horizontal cut through the darker veins. I used a pair of scissors that I had cleaned with water. Some people like to sterilize their tools to ensure that no bacteria would be on the leaf when they make the cut. Bacteria has the chance of causing rot.
Putting the cuttings in soil
I used a regular peat-based potting soil with added perlite (about 10%). Pack the soil down in your container (I used a small 3" terracotta pot) and moisten the soil completely. Let all the water drain out, then gently press the soil down again to squeeze out the last bit of water.
Next, I used a plastic knife (but really anything with a flat edge will work) to make four slits in the soil. Stick the leaves into the slits, about 2 cm into soil, with the cut side down. Then, gently pack the soil around the leaves it so that they're sturdily in place. Note that the rounder side of the cutting, which has the point where the red stem used to be, needs to be placed deeper into the soil because it'll be from that stem that new leaves will grow. The other sections of the leaf don't have to be placed as deep because the babies will grow from the veins. (In the illustration above, the left leaf will have one baby and the right leaf will have five.)
Lastly, I sprayed down the soil again just to make sure that the leaves are all well anchored.
I chose to put my pot with the cuttings on top of my fireplace. This spot in my house doesn't get any direct sunlight but on a sunny day, it'll still see around 200 foot candles because of the white walls we have which reflect the sun's light. The cuttings don't need light until new leaves start to show.
Since the cuttings have no roots, the soil must be moist at all times. I added a plastic dome on top so that it wouldn't dry up. Never once did I have to water the cuttings while they were in there. I only started to water them after I saw baby leaves spring up and it was time to ditch the dome. However, note that my plastic dome was not sealed tight. It was just sitting on top of the saucer and this allowed a tiny bit of air flow. You'll know if the soil is too moist if your humidity dome has water droplets in it.
Your cuttings should have roots after a month. You can check by VERY gently tugging the leaf. If there are roots, the leaf will be anchored down. If there are no roots, you should be able to pull it up VERY easily.
After about three months, I was ready to repot all the cuttings into their own pots! The pictures above were taken at three months. When I repotted, I tried to keep all the soil that was immediately around the leaf because I didn't want to damage any of the roots. I used the same soil mix from before.
After repotting, there's also no need to keep the humidity dome anymore. At this point, I also placed them in direct sun, right beside my south west facing window. You still need to keep the humidity level high though so be sure to either place a good humidifier beside them or mist the leaves once a day.
How do I know if my leaf cuttings have rooted?
Gently tug them, if they're NOT rooted, you should be able to pull the leaf up very easily.
How long until you saw roots and baby leaves?
My leaf cuttings rooted within a month. The first baby leaf came up in about two months.
How often did you water it?
When It was under the dome -- never. When the dome was off, I watered it when the top soil became dry.
What kind of soil did you use?
Regular potting soil with extra perlite.
Mine rotted! What caused it?
Could be that the original leaf was already unhealthy. Or most likely -- overwatering. You can also sprinkle some cinnamon on the soil to keep fungi away.
Can I propagate by putting a leaf with a stem in water?
Yes! That will work just as well but I haven't tried it myself yet.