Any potting mix will usually work, but it is important to remember peat and compost does not last more than one, perhaps two seasons. By then it will be too disintegrated and doesn't hold on to water and nutrients very well. It looses its' structure and can become very dense. Something odd happens when I use peat based stuff more than one or two seasons, it gets too compact and I've had weird issues with nutrient absorption in the plant.

The ideal soil for roses in containers is debatable, but will usually contain varying parts of garden compost (leaves, bark, canes, wood chips etc.) sand, a bit of clay, perhaps some peat, composted cow/horse manure (I swear by it), seaweed meal... The idea is to get a good texture which drains, breaths, yet still holds water and nutrients well.

With very large containers in which you cannot replace the soil every year it's a good idea to use more sand than you otherwise would do, and a bit of clay. Well composted garden waste (bark, wood chips, cut offs...) work fine as a base, and you can use some peat if you need too (holds water). If there is enough sand, and watering is not a problem, you can get by with replacing the top layer with new compost once a year, and adding some type of longterm fertilizer.

It might sound very fuzzy, but if you start with a bag of potting mix you can easily blend in more sand, dry clay powder, and some kind of fertilizer. If the potting mix has a reasonable ph (around 6) you don't have think much about it, but if you make your own from scratch and use pure peat, add enough lime (source of calsium) to get the right ph. A lot of clay can result in higher ph, it depens on the type.

If you easily can replace the soil every year you are lucky and usually any good potting mix will do. If you have trouble with containers drying up too quickly, you can add water crystals (the filling in diapers). Roses grown with organic fertilizer tend to live longer in areas with frosty winters, especially compared to roses who get water-soluble stuff like miracle grow.

This post was edited by taoseeker on Wed, May 29, 13 at 19:00

I have used regular bagged potting soil for all my potted roses for the past 7 years and have had no problems with it. I've used all kinds over the years because I usually buy what ever is on sale when I need it. As long as you water them and feed them regularly they should do fine. I like the Stay Green from Lowes and the Miracle Grow moisture control mix we get at Costco. I'm not fond of ones with fertilizer in them because I want control of when and what they get. Eventually they all get root bound and need to be root pruned and repotted and they get fresh soil then.