I think it can be any stage in the breakdown process. There's a lot of information on the Wikipedia entry, which is the first one if you google humus. I read contradictory information as to its desirability for container gardening--seems it can impede drainage as it breaks down. I generally prefer to use a soil-less mix in containers, but I haven't decided which is best. Some folks on these forums highly recommend bark fines, sold sometimes as 'soil conditioner', with or without added perlite. Some of the 'container mixes' sold, even the premium ones, seem to me to remain too wet, or to break down and pack too soon. I've also been experimenting with coir and perlite, but haven't entirely made up my mind. Always looking for the perfect mix! You don't mean a whole barrel, do you--just one sawed in half? It'd have to be a really big begonia, but there are some that would work well. What did you have in mind?

There is a large barrel in the yard under the trees. I have many begonia's sprouting now, in fact way too many for the barrel. I had some in it last summer but they weren't large at all. I posted about it and someone thought maybe it was the dirt in the barrel, maybe it needed to be replaced. It is very old dirt. It was the first yr. I've ever had begonia's and I fell in love with them. I am trying to start off right this yr. They took my breath away,they were so beautiful. I ordered more this spring. they are giant trailing begonia's. I am confused about the dirt to put in the barrel and if the wooden barrel will drain enough. I even bought an umbrella to put over it in case it rains too much. Thank God their not out there right now. We're in a flood and maybe we need to start building an ark. Thank you for your reply.

I've been reading about the rain in your area, and they say you've got days more coming. Couldn't you PLEASE send some our way? We have a very slight chance of rain tomorrow--my Mother's Day wish, by the way!--but we are in a serious drought, not normal for this area. Hope you dry out a little soon--but not like we have! Oh--if it's a regular barrel you might try filling about half of it with strofoam peanuts or some such--begonias are shallow-rooted plants and wouldn't like or need all that depth of soil. I think I've even seen where people used plastic bottles and aluminum cans.

I hope you get some rain soon. I wish I could send some your way. I can't remember what the sun looks like and I hope my garden doesn't drown. Even when the rain lets up in a few days, there's supposed to be showers everyday. I won't even be able to spray fungicide. It is still too cold to put out some of my plants. I was just starting to put the begonia's out for a few hrs. a day because they have all sprouted and read where they should be hardened.
It is 49 degree's right now!!!
Happy mothers day to you. I looked at your page and we share the same birthday. That was a surprise.
Plastic bottles it is. Makes sence to me. Thanks for all the info. Donna

Always thought that was a good time for a birthday--almost half-way between Christmases! My sisters had birthdays in November and December--hardly seemed fair!

Donna,

I wouldn't take a chance on that dirt unless it's very "loamy" (there goes another one of those words that nobody really seams to know what it means). It has to drain extremely well for the giant begonias (I like your prefix giant better than standard or pendular) and all your hard work getting them to sprout might be in vain.

The latest mix I use is about 4 parts fine bark mulch, 1 part peat moss, 1 part pearlite + potting soil till it "looks right". I would think that if water/moisture can escape from the joints in the sides of the barrel you would not have to put more than 12" worth of this mix. On the other hand, if the barrel is like a plastic pot with no drain you might be in trouble. I would remove 12" of the existing dirt and perform a drain test to see how long it takes 6" of water to escape (do it twice since the first might just hydrate the existing soil). If it takes more than 30 mins or so the second time it may be suspect. Sounds like a great location for pendular begonias.

Alexh, thank you for your reply . Testing sounds like a great idea. It has stopped raining and I will remove the dirt and test. I think I am going to use the old dirt for the blanket flower. I was reading here that they will do better in bad dirt. Thanks again. Donna