Personally, I would not choose to grow roses in containers in the gritty mix but the 5-1-1 is fine. At least in my climate, the gritty is too fast draining and watering in our dry summers would be at least daily if not more often. Roses prefer a soil that is consistently moist and IMO, the 5-1-1 addresses that need very satisfactorily.

FWIW, I grow all my outdoor container plants, including my collection of Japanese maples and dwarf conifers, in the 5-1-1 mix.

Annual repotting is not a requirement :-)) I repot only when I need to root prune....maybe very 3-5 years, depending on the plant and pot size. The soil mix is still in very good shape after that time. In your climate with more heat and moisture, it might start to break down more rapidly.

And I do add a CRF (Osmocote Plus) to my soil mix when I am potting and then again seasonally for existing container plants each spring.

Thanks for the alternative, Vivian_2010. Great idea!

I want to find an optimum soil for roses as well. Mine are in clay and just never really thrived in recent years.

That said, I agree with @gardengal48 that gritty mix is not an optimum soil for roses. I think of gritty as being a fast draining soil that dries out rapidly. It is a good match to succulents and cactus because those plant types are very good at sucking out a lot of moisture from a relatively dry soil. Most cactus and succulents will thrive in a soil that gets right to the point of drying out, at which point you water and the cycle of rapid water uptake and rapid drying repeats.

I think of roses as a plant that likes a fast draining soil that stays moist between waterings. I think of rhododendrons as being something similar, albeit rhododendrons and azaleas like an acidic soil. I guess everyone is going to recommend 511 mix, but my hesitation in trying 511 has always been that I truly hate peat moss. Aside from not being a sustainable resource, it is very hard to get it to absorb moisture once it dries, and it tends to clump in soil and make a mess that requires repotting.

With rhododendrons, I have tested with a 100% fir bark soil, and believe it or not I tested with 50% fir bark and 50% Turface. The 50/50 fir bark/Turface has proven to be an amazing acidic soil for rhododendrons. I have sister plants planted in each soil and the ones in the Turface blend have dense healthy looking leaves. I am not recommending this soil for roses or even for rhododendrons. I don't have enough experience with it yet. I am just passing along some experiments I have been doing.

Peat is just a very small component of the 5-1-1 mix but its water holding capabilities are essential to it. You can of course substitute pure peat with a regular peat-based packaged mix or with coir. btw, Canadian peat is fully sustainable - if you have concerns about this do a bit more research or investigate some of the previous discussions on the Soils forums or even the helpful contributions here by Al on that topic. Canadian peat is farmed, just like any other crop, and harvested areas are "reseeded" and even fertilized to generate regrowth. And the amount of the Canadian peat reserves that are actually worked or harvested for agricultural use are pretty insignificant in the grand scheme of things........only about 2%. And there are also environmental issues involved withe harvesting and use of coir. This is not a perfect world :-))

When used as a component of a soil mix, and especially in such a small percentage as is required by the 5-1-1, the drying out of the peat is not really a concern. I've been using that soil mix for a couple of decades under all sorts of growing conditions, in all sizes of containers and with a wide range of plants and never had it (or any peat based mix) dry out to the point where it was difficult to rewet. That is more of a concern when working peat into garden soil or using as mulch (not a good idea!!) but even that is not as serious as many claim, particularly with regular rainfall OR irrigation. Just make sure the peat is properly moistened before incorporating.

@gardengal48 in other threads here, I have been trying to get data on the water holding capacity, porosity, and saturation of peat moss, just to compare it against Turface.

What are the reasons that you feel the 511 mix would not work as well using Turface as a substitute for peat moss?

Because they are two different materials with very different properties. Cup for cup, peat has a far higher moisture retention capacity, has about triple the CEC and also offers acidity for those plans that need or prefer it. It does have a smaller particle size so reduced porosity compared to turface but I don't find that to be an issue in the volumes needed to prepare the 5-1-1.

@gardengal48 CEC would have to do with how many minerals are available for the plant in the soil? So peat moss can absorb minerals from fertilizers and then release them more slowly to the plant?

I am reading here that bark has similar CEC to peat moss. If so then doesn't 511 mix already get plenty of CEC just from its oversized bark component?

"I'm past the season to grow an Own Root Rose".

Could you clarify this? Wasn't aware there was a wrong season for ORRs.

Maybe the OP meant "bare root"?