I'm going to present why they should consider planting 4 large cement planters with rock garden plants.

The planters are 3 ft deep and 4 feet wide with rock garden plants. The planters are in a public garden and have previously been doted over with annuals by someone else. That someone else has moved away.
My group has decided this should now be our group donation to the community. Funds for plant purchases have been donated.

I'm not really thrilled with it but I think I could at least suggest something with less maintenance than annuals. The garden group members are all grandmothers who don't like working in the sun. I don't think they realize how much work this could be.

I have ordered a few library books as I know little about rock gardens. I could certainly use your expertise.

Let me describe the site and you can suggest the easy keepers I should encourage them to plant. THX

It's a full sun spot in town in NW IL zone 5a. We get 20 to 40 inches rain/yr.
It really varies that much! Yes, windy and no, I don't think there will be place to get water closeby. The planters are positioned far enough apart that they do not have to match. So it would be possible to do different varieties in ea. like acid lovers in one with the appropriate soil mix.

We have been asked to not use anything growing over 12-18" tall in these planters. So forget your basic planter design with a spike, thriller and spiller.
Although a thriller and spiller would be cool!

Karen

This could be a problem for grandmothers. Do they realize this? Windy is good for alpines. While alpines need excellent drainage, that doesn't necessarily mean they are xeric plants and do well with little water. And remember, most all perennials will not look finished the first year.

Would everyone turn their noses up if the one farthest from the water source is cactus and succulents? Even without the cactus part, sedums and sempervivums(Hens & Chicks) are varied enough to provide good diversity in size, color and shape. Rock placement would be integral in such a design.

You could use shorter forms of upright sedums like Black Jack, garden variety spreading sedums, Sedum caudicola(or S.c. 'Lidakense'), small leaf forms, Sedum 'Angelina', tiny cobweb type hen & chicks(Sedum arachnoides), ones with large rosettes, and they come in many colors. Sisyrinchium spp. (Blue-eyed grass) would go well with these too. And no fertilizing for this container.

BUT, practically no perennial garden is as floriferous as annuals. A major thing to consider.

As far as "regular" short perennials that might be good:
the dwarf forms of Balloon flower, Sentimental Blue
Blue-eyed grass (Sisyrinchium sp)
Basket of-gold Aurina saxitilis(Alyssum saxitile)or A.s.'Compacta
Pussytoes (Antennaria sp.)
Alliums
Dwarf Goatsbeard (Aruncus aethusifolius)
Low Pinks (Dianthus sp.)
Dwarf or spreading forms of Baby's Breath
Pasque flowers (Pulsatilla sp.)
Thyme (Thymus sp.)
Low spreading veronica's like Waterperry