Though I do not have to protect against Zone 6 cold, there are a few "universals" you should consider. No matter why you have to move a pot, you WILL have to eventually move it. Keep it a light material. Forget clay, terra cotta, ceramic, concrete and wood. They will either be too heavy to move; deteriorate quickly due to water and freeze/thaw; transmit cold and heat very efficiently to either cook or freeze the soil ball, hence roots or dry out too quickly. Though they don't last as long as clay and concrete in many applications, if you can find fiberglass or foam pots, they can help prevent heat build up when sun shines directly on them, and foam can help insulate the roots/soil against extremes in cold. Plus, they are tremendously lighter and easier to move. If they can't be moved, period, use the largest pot possible. A 24" diameter pot is going to insulate against temperature variations tremendously better than a 12", plus it will hold water significantly longer and permit the plant to achieve more of a normal, natural size, improving its performance in the long run. The larger, heavier soil ball will also help prevent it from being as easily toppled by wind or knocked over by the family pet or when you "hose prune". You may also increase the cold tolerance of your containers by using larger sizes and insulating their interiors using either layers of bubble wrap or thin sheets of Styro Foam. I use both here to help insulate the roots/soil against the heat extremes when clay, metal or ceramic pots are demanded. When someone else is paying the bill, there are sometimes things which are not negotiable. Adding air layers between the elements and the hot/cold pot sides can make a world of difference in the appearance, success rate and long term survival of the plants. For anything more, I will defer to those who have actually dealt with the extremes of cold. Good luck! Kim

vettin,
I grow roses in pots, I have for years.
Here are some pointers, and answers to your questions.
They sell nice durable light colored plastic containers at the big box stores, so, if you buy a nice size rose, buy a big one. They are durable, drain well, and light enough to move if you have to. (advantage of pots).
I use Miracle Grow potting mix, it works well for 2 years.
ONLY 2 years, change it every 2 years.
No composted manure in a pot.
You can fertilzie it if you want, just DILUTE it more than the instructions tell you.
Here is the watering schedule for June, July and August,
90 degree and higher, water every day.
80 -90 every other day.
70-80 every 3rd day.
Good guide line for you , but of course, if it rains you don't have to water. Check the soil.
In the winter, move the pot to a full sun location as close to your home as possible. If you can keep your pots on a porch that receives sun, that is good too.
Roses love full sun, so I would try to keep the pots in full sun all the time.
The most ideal situation for your pots, is to dig a hole in the ground and pot the bottom 1/3 of the pot right into the soil.
That is ideal, both for drainage and for the temps for the roots,
Anything other than that, well, that's the way it goes, roses are hardy plants. LOL.
Good Luck!

I only have one rose in a pot permanently (apparently -- Bengale Centefeuilles grows backwards every time I put it in the ground and seems happy as can be in a pot; we've been doing this dance for 5 years or so now...), but I can add something on from my own experiences with potted plants in general.

First, don't put rocks in the bottom of the pot. They don't help drainage (water will flow down and out, regardless) and can create an unhealthy, fetid little pool in the bottom of the pot that roots can't access. All they do is take up space where soil (and accessible moisture) can be and make the pot heavier.

Second, if there are trees with invasive roots nearby, and you have no other place to put the pot, it's good to either elevate the pot or set it on a solid slab of something, otherwise tree roots will soon be in the pot sucking out water and nutrients -- they love that potting soil, too. Here it's the fig tree and the laurel that are particularly bad but I imagine maples or birches and such could be pesky elsewhere. I elevate pots off the surface of my soil, anyway, because it has a clay-ish consistency that can, and has, plugged drainholes.

Here it is the rare plant that will survive outdoors in a pot over the winter, although some people on this forum have succeeded by burying the pots in mounds of leaves. For me the easiest and best solution is to store the dormant plants in pots in an unheated garage over winter. They only need to be checked about once a month to see if they need watering and usually do not. They generally require watering about 2-3 times from early October to mid-March. All zone 7 and hardier plants have survived this with the sole exception some roses. When I have that figured out, I'll report back.

For potting soil, I use Fafard either 2B or 3B and recommend it. I also use Soil Moist to ensure a more constant soil moisture.

I agree with Kim that larger pots are better for the reasons he stated.

Cath

As catspa said, do not put a drainage layer of any kind in the bottom.

In your location, winter protection is needed only for the coldest part of winter, say temperatures dipping below 10 F, or long hours at 15. You want to keep the plant cold and dormant all winter but with the interior soil above 20. Growing out prematurely can be a big problem if you put them in an attached garage too early or leave them too long. Leaving them outside against a south or east-facing foundation is good, and you can pile leaves around when severe cold impends.

If you have one, use a regular dolly to move big pots, or put each one on a wheeled platform available at garden stores. A regular dolly can negotiate steps.

The Container Growing Forum has great information about mixing soils. Or, among ready-mades, Miracle Gro for Orchids is durable enough to last several years. It is mainly bark and peat.

Good advice here so far -- I just wanted to add that I bought a few large planters from Home Depot for just $20 each for my pot-pet collection of red HTs. They look like wooden barrels but are made of resin. You'll have to make the drainage holes on the bottom, but they're already marked off. They measure 22 1/2 inches in diameter across the top, about 16" in diameter across the bottom. Here are a couple of mine with roses but before I add annual "fillers and spillers."

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On the Home Depot website, these planters are for some reason listed twice, with two different pics -- but if you look at the descriptions, you'll see the same sku# for both. The angle of the pic in the second link makes it look more tapered than in real-life.

http://www.homedepot.com/p/Unbranded-22-5-in-Resin-Whiskey-Barrel-HDR-505742/203580708

http://www.homedepot.com/p/Southern-Patio-22-1-2-in-Whiskey-Barrel-Resin-Planter-FGS-468573/202294014

For the HTs that don't get as large, I found these pots for $10 each at Rite Aid (they were on sale, normally $20 each). There weren't many at a time, so I bought all I could find when I saw them on-sale -- and as such, I ended up with four red, three terra-cotta, and one brown. They're about 15" in diameter across the top. These I'll likely stick in the garage or on my enclosed back porch for Winter, but the larger pots I'll leave out, perhaps mounding Autumn leaves in them and covering with burlap.

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Be on the lookout for on-sale pots at stores where you wouldn't assume to find them!

:-)

~Christopher

You are suburban DC, I think?

It is warm enough that I don't think you want to move pots in for the winter. The idea is that they should be cold enough to be dormant, but not so cold to cause permanent damage. Up against a house foundation is a better location, though you may not be able to do the zone pushing others do with a warmer overwintering spot. Since this isn't a reasonable place for the roses during the summer, they must be movable. The largest pots I can reasonably move with a handcart are about 20". If you have hefty helpers, that could change.

I am in Alexandria and have about 15 roses in pots on my patio--shrubs and teas. They make it through winter fine. I don't move them at all.

catspa, what does a rose growing backwards mean? I've seen this term before but never knew what it meant.

View1, "growing backwards" refers to decrease of plant size over time as canes die back rather than producing new shoots and growing. Unhappy plants shed parts that for myriad reasons can't be maintained, gradually becoming smaller rather than larger. In the case of 'Bengale Centefeuilles', the plant I have doesn't seem inclined so far to build a root system robust enough to cope with my ground conditions; grows okay and blooms wonderfully in a pot, though.

catspa, sorry for the delay in responding. I was out of town, busy with family & just saw your post. Thanks for the explanation.