Usually a porous mix is best for most types to provide excellent drainage. I usually use a good potting mix (Miracle Grow lately since you can buy the large bags at Sam's) and Perlite. I try for a 50/50 mix.

I think it would be interesting to hear more about what people use for potting. I started out mixing my own and still prefer to experiment. Someone who used to post on here said she used straight bark fines and found that most useful. The best bark I could find was hardly 'fine', so I added perlite. I've also been experimenting with coir and perlite, and I think I like it. Of course, any of these need added fertilizer. Just got through reading a link that included negative information about Miracle-Gro--the fertilizer, not the mix, tho' the mix I've seen had the fertilizer added (the mix I've seen out by my potting bench, that is!) The referred link said it has damaging salts. Seems to me I've read that elsewhere too, but I don't know how reliable the information is.

Hmm, I use Miracle-Gro & Schultz fertilizers with no adverse effects. I water at half the recommended rate though and only through the growing season. Don't all chemical fertilizers build up salts though? It's probably a good idea to repot every so many years anyway not only to get rid of salt build up but give the plant some new soil. I know some people repot every year but that's just too much work to do.

I also heard that MG will fire employees who smoke but again this may be another rumor.

I agree with experimenting as well. I fill the bottom 2/3 of my large pots (18 inchers) with Nature's Helper which is a much finer shredded pine bark, more as a cheapskate than benefiting the plant. I've also used it as a mix for sticking larger leaf varieties such as 'Caribbean King' and 'Caribbean Queen' and it propagates just as well as expensive potting soil.

i really think what soil you use is a really variable questions. it's going to depend on the habit of the begonia you're growing, how picky it is, what stage of life it's at (newly potted starts vs. established plants) and where you live and will be growing (greenhouse vs. indoor houseplants, arizona vs. louisiana).

in general, it's always a good idea to start out with quality soil. in addition, you'll want good drainage for begonias. i've heard great things about Pro-Mix HP (hp stands for high porosity) for growing in greenhouses, but i usually just buy some good quality soil (lately, black gold) and mix in perlite.
you'll want to really be observant of how your mix does and amend it accordingly. for instance, you can add perlite for drainage, as well as sand and pumice. perlite tends to float up to the surface of the soil after awhile so having something heavier in the pot is advisable.
if you are growing in an enclosed environment such as a terrarium or bubble dish, you might want to consider activated charcoal to cut down on pathogens, as well as chopped sphagnum moss.
if it tends to dry out a lot where you are growing (i.e. indoors in winter time), peat moss and vermiculite will hold more moisture. one thing i've found is that no matter how great a plant is growing in the greenhouse i brought it home from, my house is definitely less humid and i'll probably need to change the mix soon after purchasing.
i don't think i've ever used a mix straight out of the bag. it takes awhile to get your potting medium just right for where you live, and i'll be the first to admit i've killed a lot of beautiful begonias trying to figure things out!

good luck, hope that all made sense!
-ming

Perfect sense. I might add that some begonias don't fit the norm either. Some appreciate a lot more moisture ('Big Mac' for example loves lots of water) and some prefer it on the drier side ('Cowardly Lion' is a good example).

promix.

I'm mixing Miracle-Gro Moisture Control with perlite and peat moss. I'm probably at 50% perlite, with the brown stuff taking up the other 50%.

Here is a link that might be useful: Fred's Begonias

I quit using peat moss in all my pots - stays wet too long. Last summer I used straight Miracle-Gro (not the moisture control) with no amendments for all new begonias and maybe half of my old ones and they all grew beyond expectations. I wished I had the time and energy to repot every pot each year but that is a monumental task.

I too use very little peat moss if at all in any of my mixes..
My mixes use to compact to fast, break down rapidly, impeed drainage and airation of roots, hold water far too long, and become water repellent if forgotten to water. Not to say also attrack "fugus gnats", which eat the small fine hair roots, all causing eventual root rot.. I could never keep one alive for more than a year, unless I repotted over and over again.

I use a mix with 5 parts bark, 1 part peat or turface, or pumice, and one part perlite..The larger the particle sizes, the better drainage, porousity, and the avoidence of compaction in a short time.

My begonias now flourish...

Mike..:-)

hcmcdole, I hate to burst your bubble but... "straight Miracle-Gro" is mostly peat and maybe some "forest products". Mostly bark.

Thanks Frank. Whatever is in it does great for me.