Question about potting mix

[Ian Y]

This query just in for Paul :

"Hello,

I happened to come upon a photo of an Edelweiss plant in your one of your "Wisley Logs" for June 2008.    I have recently started growing this plant, and this past June, I had plants (both in the ground and in pots) flower.  However, I find that the plants in the earth do much better than those in pots, and I was wondering what soil mix you use for your plants?  I realize that there are other factors in play here, considering that these are alpines, but I was just curious because the plant in your photo looks quite healthy.

Many thanks!
  -Ben"

The photo from the Wisley Log Ben refers to is shown below-

[Paul Cumbleton]

Hi Ben,
We grow this plant in our standard alpine potting mix which is equal parts of John Innes No. 2, peat, perlite and grit (to which we add in a little fertiliser of Vitax Q4 and a little dolomitic limestone to adjust the pH to 6.5). I suspect the difference between your plants in the ground and those in pots will be largely due to better moisture levels in the ground. These plants seem to want more water than your average alpine, so frequent watering is important. We also find they do better with just a little shade, at least here in the South East.

Cheers

Paul

[Ben M]

Ah, ok thanks.  The plants in the ground are growing in very clay-rich soil scattered with gravel; however, it often gets rock hard dry, at least on the surface.  But I figure it still has more moisture, anyways.

I have been growing that one Edelweiss in a deep plastic pot filled with mostly perlite and sharp sand, with very little organic matter and a few pinches of limestone pellets.  I researched online, and one soil mix suggested roughly 6 parts of inorganic matter (grit, sand, etc.) to 1 part compost.  It obviously stores very little water and nutrients, and so I worried about how it would fare.  But these are hardy plants, and they did flower this year, but they didn't look terribly healthy.  I am now considering moving it to a clay pot to cool the roots down, and I'm looking up websites to purchase John Innes compost, as it is rather unknown in the US.  There are no composts here that I know of that are loam-based, most of them containing large amounts of nothing but peat and wood chips.  

Thanks!
  -Ben