Thursday, June 27, 2013
Needs Well Drained Soil
As I continue my fascination with rock gardens I keep coming up against plants that are hardy to my zone 5 but often die in the winter, not because they are damaged by the cold, but because they rot in the winter-long water-logged soils. I ran into this problem years ago and recall being perturbed by the garden centers that sell drainage sensitive plants like Aster frikarti, Lewisia, most Penstemons, Incarvillea delavayi (hardy gloxinia), many Agastaches, and most Veronicas without a word about drainage. Now that I am being introduced to more and more plants that grow in gravel, screes, sand, and rockeries I have become much more interested in this issue. I was pleased to see that the New Mexico nursery High Country Gardens was saved from bankruptcy. They offer a plethora of plants native to the west that would be hardy here in Ohio but just won't take our wet winter soils. I, like most any plantsman, want to grow those cool looking plants from the west as well as the ones already well known to me (such as the ones above) but that are likely to die over the winter without appropriate growing conditions.
I decided to experiment with a bed at Kingwood Center. I excavated several truckster loads of the underlying clay layer and replaced it with copious amounts of sand, incorporated into the remaining upper level soil layer. When I thought I had enough sand I added some more, because I know sand can just sort of disappear into the soil matrix unless you really add a lot. Now I hope I didn't just build a bathtub.
Then I started looking around for suitable plants. I asked one nursery we deal with regularly what plants they grew that would fit this definition. I enjoyed their reply when they said anything like that would be dead at their nursery. One plant I wanted to try was Euphorbia x martini 'Ascot Rainbow'. I first saw it last year when it seemed that every garden center was offering it as a good zone 5 plant. (Drainage wasn't mentioned on the tag.) I was skeptical but bought some anyway. They were profoundly dead in the spring. I later read that it needs good drainage and also saw we were even selling them at Kingwood Center. I had to find out if it will perform as claimed. The survival of another selection may be wishful thinking. Every mention I read of Stipa gigantea (Giant Feather Grass) was expansively enthusiastic. Mostly it was listed as zone 7 but one authoritative reference said zone 5, everyone said good drainage is a must. I had to try it. I bought one for home and one for work. The balance of the plants selected for this experimental bed were similarly inspired. Everything has had a good start as can be seen in the above photograph. I will know more in the spring.