just a tip, that i learned on the forum, and is helping in my window boxes, even more than the water crystals, is lining the bottoms with baby diapers! my boxes leak around the edges some, so i didnt even punch holes in the plastic liners. every year but this one, my window boxes have bit the dust--literally !

Carrie - you could maybe start with some of the drought-tolerants like any prarie plant (daisies, rudbeckia, cone flowers, etc). Others might include what one of my sisters is growing along a dry west-facing bed - coreopsis, roses (shrub roses might be good), spirea, asters, monarda.

In fact, you know what might be good if you get chance - if you can, try to ride along Delaware Ave./Columbus Blvd. and look at what they have planted out there in the center median strip. It's incredible whoever landscaped it. There is a continuous series of some shrub or perennial in bloom amongst those plantings that I think run mainly along the Penn's Landing area, from about Locust (or perhaps further south - don't remember how far), all the way to Spring Garden (or perhaps past that - I haven't gone further north to see). Those plantings are in full blazing sun all day long, plus they are obviously exposed to alot of vehicle traffic and fumes, and it's just unbelievably beautiful. My sister and I have been trying to ID all the stuff that they have planted along there just to get some ideas and anything that can grow there without babying should do okay on a roof. Right now there are alot of some variety of shrub rose that have many many clusters of small double flowers blooming along that strip. Those are interplanted with other things - from what I recall, alot of blooming salvia and coreopsis "Moonbeam".

Some good drought tolerant annuals/tender perennials might include Madagascar periwinkle (also called Vinca - but the upright flowering kind), wax begonias, New guinea impatiens, nicotiana, petunias... And you might even consider getting them some bougainvilla, although that would need to come inside for winter. But it thrives on hot/dry.

Just some things to think about!

portulaca is the only thing that will survive and thrive in pots all summer at my house.

They thrive in hot dry climates, will only bloom when the sun is shining and they come in some real eye-opening colors.

Thanks folks!

Jenny, funny that you mention Delaware Ave. I drive by there almost daily, and live two blocks from there.

I did think about using perovskia (russian sage) and some of the other plants I've seen there for the two large pots. (btw, my very old offer to give you a tour of my community garden, including fig trees (!) at 4th & Christian, still stands).

Where I'm running into a little challenge is that there will be quite a few smaller (6-10") pots in the planting. Too small for most perennials to survive, especially without consistent watering.

Gurley, I plan to use portulaca heavily! They want stuff with color, that will bloom for the rest of the season with intense sun and not a lot of water - so portulaca is the one I know can handle it. I think even most other "drought tolerant" annuals will have a tough time of it.

Thanks again for your advice, and any additional will be happily recieved.

CarrieB

Carrie - I really do need to make the time to come visit! I have probably driven by it as sometimes I'll sometimes go down 4th St. on the way to Oregon (there's that pet store at 2nd & Oregon).

I drove down Delaware Ave. yesterday and noticed there are some ornamental grasses out there - possibly miscanthus. That's something to consider too as I know they can take full sun.

Russian Sage is an excellent idea for the larger pots! OK I am biased (user name). The newest, " Little Spire " does not get nearly as wide as the original. 18" spacing seems to be plenty, it does get up to 2.5 or 3 feet tall, regardless what the tag may say. Little Bluestem is a nice small drought tolerant grass. "May Night" salvia is also quite drought tolerant. Do you bring the containers inside for winter? If not I need to know how you keep them alive.

sage lover, I don't bring my personal containers in for the winter - they overwinter just fine. My containers have hosta, lamium, creeping jenny, sweet woodruff, pieris japonica, kalmia, boxwood, norway spruce, hardy geranium, heuchera and several types of sedum. I do nothing at all to keep them alive over winter, and with the exception of the kalmia (which doesn't seem to like being in a pot in the city) all else thrive and grow every year.

The containers I'm working on are for clients who don't want to water a lot. They won't bring the containers in for the winter either. There are annuals and perennials that I plan to put in those containers. I hope that most of the perennials overwinter.

I agree that portulaca is about the only thing guaranteed to thrive under these conditions. Maybe some of the sedums? The variegated ones have some color.

Why are the clients insisting on the small pots? Can you convince them to go larger?

Water crystals are good but I'm not sure how many seasons they last - depends on the brand I think.

Carrie,
We went away on 6/11 until 6/14, that is when we had that "heat wave"? Welll, no one watered my plants for 3 days...
I watered everything really well before we left but I still lost some things. Luckily, not too many!
Anyway, I have lavender & mint in a big old long stone planter. There is also a moon flower vine & thunbergia on each end. They all survived. The lavender & mint are a few years old, the planter stays out all winter, I never move it. These are beside a chain link fence so maybe that helps a little as far as blocking sun??
My sweet potato vines survived, they are in two big old cement urns.
Of course, portulaca always survives!
What about hens & chicks? My mom has these in strawberry jars & they are many years old. Survive anything.
I guess there is no way you could provide any type of shade up there?? Maybe even a little trellis or tiny umbrella??

I like pro mix soil also, seems to stay better than anything I ever used before. Doesn't get hard & dried up like other soils.
I just bought a LARGE bag at Creeks Edge @ 2 weeks ago.

Good luck!

this is what is doing well on my rooftop patio. Lavenders (spanish and english), sages, catmint, african daisy (symphony series), Cerastium tomentosum 'snow in summer', lobelia, lemon thyme, lithodora diffusa 'alba' and 'heavenly blue', petunias, geraniums, and mini roses and some ground cover roses. I water once a week or even less, sometimes more. What isn't doing well - impatiens, fuscia, gentians, phlox divaricata (canadian phlox), heliotropium aborescens. I get sun from 12-sunset and it isn't too windy and everything is in pots or window boxes.

Thank you again everyone! I've got the plants, a mixture of portulaca & sedums, perovskia, catmint, yarrow, gazania and a bunch of other drought tolerant annuals & perennials. Also an herb garden of only drought tolerant herbs.

The clients say they will water once or twice a week, and I'm hoping that will be enough & that they water thoroughly. I've got two large containers, and a bunch of smaller 6-10" pots that I hope will do OK.

The planters will be installed Monday (& maybe Tuesday as wel). Thank you again for all of your great advice. You all are a fountain of knowledge.

I was going to say portulaca too but a couple beat me to it. This stuff flowers and flowers and is kind of like a dessert type plant as it can go a time without water because of the thick leaves that must store extra water.
Lesley

Carrie - wish them luck. The heat pump from the soon-to-form Bermuda High gets turned on Friday and will be in full effect all next week, so they will be "tested"! ;-)

Add fountain grass to that list. I like lavenders too. Also think of rosemary, the cascading types.

But my most drought tolerant plants are my collection of hens and chicks. I've several of them in contrasting colours set up on a very narrow trough. Plus I've used lots of different echeverias in the mix.

To me, if you are going to water only once or twice a week, what is the point? They will hardly get to see their plants! *sigh* to each their own I guess. I hope that they are happy with the choices you have made for them.

Dear Carrie,
So, the summer is over - how did the pots survive. I've given up on small pots - the bigger the better.
And I have gone to self-watering planters for my south facing deck, and I have three umbrellas on the deck that I use to shade the floorboards so that the relected heat is cut way back. The first summer I placed pots right on the deck, the plant foliage literally 'cooked' from the reflected heat. Now I keep my pots up off the deck and they manage to survive only being watered once or twice a week. Water absorbing crystals help, too. And wooden planters help insulate the roots from the heat, also.

Sorry to dredge up this old thread, but I'm researching drought-tolerant container plants and found this very informative. If Carrie is still posting here, I wonder if we could get an update on the roof garden and how well it worked out?

Any plant in a container will need watering more often than the same plant in the ground. Container plants are completely dependent on being watered externally; there's no ground water to draw upon. A plant that can go a week without water in the ground during a heat wave may have to be watered three times a week in a container.

eldo1960 makes an excellent point that plants in containers are very different from plants in the ground. There are at least two different kinds of "drought tolerance" and it makes a big difference when it comes to container gardening. Some plants are drought tolerant simply because they have very deep taproots that can find moisture that most other plants can't--Datura and Ricinus are two examples. These plants have to have a constant source of moisture, but are good at finding it. These plants often do very poorly in pots because when the soil in a pot dries out, their roots dry out.

Then there are those plants that can be bone-dry, roots and all, and recover. Most succulents (e.g., cacti, Sedum, Portulaca) fall into this category. Plants in this group generally make better container plants because every pot is going to dry out sooner or later, and it's this group that I'm trying to get more information on.