I think the most important thing is humidity - do keep them covered while rooting. You can experiment with different types of media - Perlite is probably one of the best, a mix of good potting soil and Perlite, but you can also use shredded bark, sand, gravel, etc. Water rooting works well with most cuttings but not all. Again cover cuttings with a baggie or other clear plastic container EVEN IN WATER. Place as close to indoor lights as possible or in a bright window (not direct sun but this isn't necessarily true either).

Anyway here is a link that might help:

Starting new begonias from cuttings

Do you have a picture of any begonias rooting in water?

I've found tuberous varieties much more difficult to root than others, I think because their stems have a much higher water content. I'd recommend taking cuttings farther down on the stem (they need to be very firm), using a fugicide dip (rooting powder contains this, and I believe it's more helpful than the hormones included), and inserting them in a moist, but not soggy, sand/perlite mix with very little peat at first. Cut off the distal ends of large leaves, and enclose with a loose cover to provide some humidity (but not enough to cause condensation which will drip onto the plant and cause rot). I definitely wouldn't try rooting these in water, and I've never heard of success using leaf cuttings of tuberous begonias.

Hope this helps!

I agree with bubba if you are propagating tuberous (guess it helps to know what they are trying to propagate). It does seem a lot harder to root than other types of begonias but Perlite is one media that has worked for me in the past. I wish I could find the web site that shows a lot of success with propagating tuberous by leaf cuttings - they make it look so easy.

The one I were trying to propagate were Rex's.

I found the web site that shows how to propagate a tuberous begonia from a leaf cutting (really a modified leaf cutting).

Scottish web site

I saw leaf propagation demonstrated by a nurseryman from Parks Seed Co in SC. He propagates thousands of cuttings each year. He said he uses a good/quality potting mix (looked like peat/pearlite type of mix). He placed a wick through the bottom of the pot up into the soil so watter could absorb from a tray below the pot, rather than top watering. He also recommended a humidity dome with a couple of holes to allow for some air movement--said stale air breeds disease and is a major enemy of propagation. His demonstration dome looked like about 8" x 12" and had a couple of 1" square holes with adjustable openings.

He fills the rooting pot to the top edge of the pot with the mix so there are no "pockets of uneven humidity" that can breed disease on the cuttings.

Never use scissors for cutting! Scissors crush the cells leading to disease. Place the leaf upside down and cut with a very sharp knife. Cut the leaf into several segments between the veins.

Stick the cutting into the pot and firm the mix around it.

Then he puts in indirect light such as on a sun porch or near a window covered by shears--NOT in any direct sun at all.

He also noted that "cane-type begonias" (segmented stem sections) cannot be leaf propagated. Take a cutting with two or three leaves and root stem directly in moist potting mix in the humidity dome.

Also, below is a link from a previous thread from 2005 titled "Begonia propagation for newbies". It has photos that may be helpful.

Here is a link that might be useful: http://forums.gardenweb.com/forums/load/begonia/msg1022105325400.html

Hello I have done a video of the proper way to propagate begonias via leaf cutting through the video I go through a few ways to propagate a begonia leaf https://youtu.be/KQu_H3Yroa0 here is the link if you wish to check it out thanks

What about Rex begonias or other leaf begonias? I remember reading about the leaf method years ago where you cut slices in it and lay it on potting soil with pins holding it flat. Anyone do that?

Yes I do Larry but with out pins and also whole leaf where I do use pins in this video here https://youtu.be/KQu_H3Yroa0 

Larry, there are many methods to do it by leaf - from simple water rooting to cutting in wedges and any semi-sterile media will work to varying degrees of success. The Jiffy pellets work very well for almost any cutting and is easy-peasy. The mesh is my only objection since it does not break down but roots easily grow through it. So you can start 72 in a long tray or 36 in a square tray.

The key is keeping it fairly sterile, just the right amount of moisture (some of the big succulents leaves are best to go down in almost dry media since there is so much moisture in the stems) which means not too wet but not totally dry either. Humidity may be the biggest key in propagation. Healthy leaves also is the best to go with. Too old or too young may quickly die or slowly die using up its reserves.

Here are a couple methods I've used.

A simple lettuce container from the grocery store with about an inch of potting soil on the bottom - no water because the media was semi-moist. Stick the cut stems in an inch or two and close the lid, place under lights (simple shop lights), and let nature work.

A Jiffy tray with peat pots and potting soil. A high humidity lid was used to cover. These are all stem cuttings

How the pros do it: (they start out with wedge cuttings in very small containers with virtually 100% success). Then they move up the plantlets to a slightly bigger pot and then to 3 inch pots, then to 4 inch pots, then 6 inch pots, and finally to 8 inch pots.

And one of my 72 count Jiffy pellet tray with lid removed. Easy but the problem is moving 72 plantlets to the next size (I used 3 inch pots) requires four times the shelf space. If it was four inch pots then it would be six times as much shelf space. You get the idea.