Maybe prickly pear (Opuntia humifusa)? It's succulent, has wide leaves, and is native to the area (so it can tolerate the cold and heat).

Being in an urban area can raise your zone by at least a half, especially on the SSW side. That might be negated by a 16th floor location, though.

'Autumn Joy' sedum, or some of the newer varieties, should work. They do well in pots. They do go dormant in winter though.

There are some really cool yuccas on the market now.

Great ideas--thanks! The basic Autumn Joy is good, becaue even though it dies in winter, the stems look good for a long time brown. And I hadn't thought about using Yuccas, some of which are totally hardy here.

BTW, it's only a 4th floor location (top floor, but just a walk-up), but with the fact that everything's in pots, I figure I should err on the cold side, rather than trying to assume warmer (even though I'll be in the center of dc); the freezing and thawing of pots on a roof are probably problematic . . .

At the delaware shore, on the other hand, I've been pushing the zone map MUCH more--have several zone 8 things, which we will cross our fingers about (but there *are* pomegranite, italian cypress and eucalyptus in town, all several years old . . .)

Thanks again!

Here is a link that might be useful: the DE, not DC, place . . .

Hello:

Just this last weekend, I was touring a garden in Silver Spring that had loads of cool succulents & cacti (especially agaves), many of which were growing far out of their normal zone. The gardener claimed that there were 2 main things that he had done to help these plants succeed. First, he had a site with strong southern exposure & steep slope. Second, he used special cactus soil in these beds - lots of gravel & sand & no organic matter. These factors helped him get around the normal problem of rot over the winter months.

If you check out the Plant Delights website & the Yucca Do website, you will certainly find some more interesting succulents to play with. Even if you aren't so adventurous as to try agaves & such, there are a lot of smaller sedums that have interesting leaf texture & shape; I can supply species names, if you're interested.
done

If you would like more details, please email me. I might be able to put you in touch with the fellow in Silver Spring.

Wow--both nurseries are new to me. Great list of Agaves and other succulents. I've been a gardener since, like, 5 years old, but never did anything with succulents. I had no idea there were so many options (had I known, I might have done a more xeriscopic garden near the shore!).

A friend who had a windswept rooftop garden used to loosely wrap insulating blankets (the ones used to wrap hot water heaters) around his pot groups (not individually), for the deep winter, just tucking in the edges. I think he used 3 of them that he had cut in half widthwise. Then he put plastic painter's drop clothes that Home Depot sells on top of the isulating blankets to keep the rain from damaging them. He had used the same blankets four winters in a row by the time we lost touch with each other. The rest of the year, the blankets and drop cloths were stored in his storage bin in the building basement.

This kept the pots from freezing and thawing and let him overwinter stuff that otherwise might have died.

Could also set the pots in groups into a larger tub or such, packing in some dry insulating material, such as leaves, to slow temperature change in the pot soil.

I grow 'Autumn Joy' in a container (going into its 3rd winter now) on a 6' x 40ft covered balcony on the 18th floor of a hi-rise and it has done just fine. It is part of literally dozens of shrubs, perennials, bulbs (and now a tree) that I leave outside for winter on the balcony.

I also have an opuntia humifusa that I leave out in winter (also going in its 3rd winter). What I've done with the hardy succulents and cactus was to put them where they can stay moderately dry and I can control the moisture. I think in a completely exposed rooftop type environment, placing under a table might give the same effect (same would apply with container bulbs too). Both of those that I have are not wrapped or "sunk" or given any extra insulating protection. The sedum spent its first winter in a 1 gallon nursery pot (never got chance to pot it up that fall) and spent its subsequent one (which will also apply this winter) in a 12" foam pot. The cactus is in a 8" clay pot (my only clay container for an outdoor plant). I prop the cactus pot up on top of one of my window air conditioners in winter, which puts it far back from the rail and out of the rain and snow.

I've also wintered other sedums (mostly creeping), as a "ground cover" for my container clematis and didn't need protection for those. I think a hardy yucca or other hardy agave would do just fine without any extra protection.

Again I think the completely open space as opposed to my covered one, might necessitate observations of the wind patterns and even snow drift patterns up there, in order to give consideration for placement of containers during winter to account for that. And I would agree with BraSpadya about perfectly draining soil to help to avoid rot due to soil staying too wet for too long.

This is my sedum and cactus last year (I am WAY behind getting my this year's pics off the camera... lol). The sedum is blooming right now and the cactus has a bunch of new pads this year though.

{{gwi:26803}}

Here is a suggestion for a planting that should work on a rooftop in DC. I grew these plants in the ground when I lived south of Harrisburg, PA. When I moved to Rehoboth Beach, DE they were transferred to large pots and hypertufa tubs. I have a fairly large collection. The one shown is in a 14" bowl. (Echinocereus coccineus) The bloom period is June, usually including Fathers Day. It remains outside all year in a sunny position.

Click on thumbnail for larger image.

Al

Wow Ariole,

those are great plants. I didn't think anything that colorful would grow in our zone. I saw lots of outside succulents in California, but not really here...just the sedum, hens and chicks, the usual.

I'm interested in why you specified succulents. You could probably grow some interesting subtropical plants in that environment - it would be like zone 8, I think.

The reason for succulents: It's a roof terrace facing south-southwest, and we are often gone for a week or two at a time. I don't want to have to set up a watering system. Succulents (and maybe some cacti) seemed just the thing.