I would repot it when there is a forecast favorable enough that you'll be able to leave the plant outdoors for several days after the repot. I've grown several begonias in the gritty mix, most of them dwarfs, as companion plants for bonsai being displayed. All have done very well. If it's your first experience with the gritty mix, expect water to run through the soil quickly. The soil does hold more water than you think it does, but you will need to water more frequently; and because you'll be flushing the soil when you water, you'll need to fertilize more frequently as well.

Using a short wick as a 'tell', to let you know when water is needed might be a good idea until you're up to speed. It does take a little getting used to, but I think you'll find it to be an exceptional soil for all your long term plantings once you do.

Best luck, Susan!

Al

Thanks, Al. This is my first experience with this particular begonia, and it is probably the first one I've had that really will have to come in in the winters. It is only hardy to in Zone 10, and people who have tried to keep it outdoors in the SF Bay area seem to think it doesn't kill it but sets it back just too far.

At 67, I'm not big on hauling heavy stuff in and out of the house, and this girl is likely to get BIG. Also, she apparently doesn't like to dry out between waterings, so she will keep me on my toes in the gritty mix.....No forgetting her for a few days the way I have been able to do in her current mix which is more like (or maybe even exactly) your 5-1-1.

Please keep us posted. ;o)

Al