starting begonias in pots

[maglonian]

I'm thinking of starting off begonia corms/ tubers in pots but am totally unsure about a couple of things.

1. Size of pot that is adequate ?  I've some 15cm x 15cm pots ... are they big enough for the initial starting off ?

2. Potting medium ?  Gritty multipurpose or something more substantial like a John Innes #2 or #3

As usual all advice gratefully accepted and received

[Tig]

It depends on the size of the corms as to what size pot they need. I tend to stick mine all together in a large tray of mpc as soon as they show signs of growing. Last year they started a bit early and it was a nightmare trying to keep them tidy before it was warm enough to plant them out. I only put half the corm below the surface level of the compost when I start them off, then plant them properly when I put them out, their roots lift the compost out of the tray if they are kept moist but not wet.

[maglonian]

Feb 20, 2017 0:10:53 GMT Tig said:

It depends on the size of the corms as to what size pot they need. I tend to stick mine all together in a large tray of mpc as soon as they show signs of growing. Last year they started a bit early and it was a nightmare trying to keep them tidy before it was warm enough to plant them out. I only put half the corm below the surface level of the compost when I start them off, then plant them properly when I put them out, their roots lift the compost out of the tray if they are kept moist but not wet.

Thanks Tig

Now all duly sat on a couple trays of mpc.  
Maybe a bit prematurely as conflicting sites say they shouldn't be planted until you see growth but others say it's ok to plant before growth 

Time will tell.  Must admit to being surprised at the size difference between Wilko's 3 for £2 and an Aldi special - 6 for 99p ... definitely get what you pay for in this case

[maglonian]

Another question

Will begonias thrive in any good soil or is it best to add some peat moss to the mix to make it slightly acidic ?
Complicated stuff this gardening lark.

On the acidic thought ... has anyone used vinegar to amend soil or is peat moss a safer option ?

[andy]

General purpose potting compost is absolutely fine for Begonias if you are growing them in containers. Any good garden soil is fine...nothing needed really except maybe a bit of growmore.

Don't forget that Peat is inert. It will lower your pH but it has no nutrients in at all.

Never used vinegar, i'd imagine it wouldn't do much good for the soil or it would just drain away.

[maglonian]

Thanks andy,. I only mentioned the vinegar to make soil more acidic as I saw it on an organic website and thought it was strange as you can use vinegar to kill weeds.
The peat because one website said to use 2:1 mix of peat moss and MP to grow begonias in containers. I guess the internet has so much conflicting advice ... is why my GP banned me from using it I guess

On the subject of growmore in pots ... the label says 70g per square metre, what would you use say every 10 litres of compost ? I can't seem to find the answer anywhere and feel a pain asking so many questions here