Expert: C.L. Fornari - 11/1/2007

Question
I live in the Philadelphia, Pa area.
I would like to plant some plants on top of a 2 foot high retaing wall.
The soil on top of the wall is about a foot deep with stone below.
I would like  some plants that will live year round so i don't have to put plants in ever year.
What would you recommend that won't grow to big ?
I would like them to be no bigger than 1 foot in diamater.
If possible is there a plant that would also flower ?
Can i plant them now or do i have to wait for the Spring to plant them ?

Answer
Desgnr,
Since there is little soil and it is stone, which will absorb heat, you'll need to plant drought tolerant plants. I'd recommend using a variety of sedums and hens and chicks (Sempervivum) - you can get both of these perennials in many foliage colors, from lime green to burgundy and purple. Most sedums flower as well, pink, yellow or white, but with an assortment of foliage colors you'll always have color on the wall.  

If you want a sedum with some height, plant Sedum 'Autumn Joy' - as long as you don't fertlize it very much (an application of an organic fertlizer in the spring is enough) it will stay the height and width you want.

Be sure to use new top soil (loam) in the wall - NOT potting soil. Most potting soil is actually soilless potting mix made of vermiculite and peatmoss - you'll need real dirt if you want the plants to live over the winter.

Plant them next spring - you'll have a better selection of plants in the garden centers, and they're more likely to make it through the winter because they'll have had an entire season to stretch their roots into the soil.

If you want to add a few annuals for summer flowers, use Portulaca - both the regular "moss rose" type available in six packs, and the Purslane varieties from Proven Winners are great and they blend well with sedum and hens and chicks.

I hope this helps!
C.L.
www.gardenlady.com