|Perovskia and the water puzzle
Last fall I transplanted a Russian sage to a bed whose position atop a terrace step creates sharp drainage.
Perovskia atriplicifolia (not actually from Russia and not really a sage) doesn't have much of a root system: just a few thick storage roots, and not much in the way of the fine root hairs that hold together a ball of soil. When you dig it up, the soil tends to fall away and leave you holding bare storage roots.
But root hairs take up moisture. The leaves wilted; I cut back the stems to reduce transpiration surface area. I took a spray bottle out to the bed, and left it there so I could mist the plant several times a day.
I couldn't just water it a lot, because perovskia hates wet soil; the roots rot. Though root hairs absorb moisture, they fail in drought. This plant prefers drought. It probably relies on symbiotic mycorrhizal fungi, which function like root hairs. It also grows deep, accessing soil water reserves not available to other plants. (The first time I transplanted the perovskia, I didn't dig deep enough, and it regrew from what I missed.) You have to water the transplant deeply, to encourage that deep root growth while not watering too often; so the soil drains: a tricky balance.
The leaves died one by one; I kept misting. Eventually the stems were bare, whitish-gray sticks; I kept misting, telling the plant "I know you can do it." Finally a tiny bud of gray-green emerged. By the time frost came, a dozen lacy, finely-divided leaves had unfurled.
Were they too young? Were they hardened enough to survive winter? In spring, I was sad to see the plant had disappeared: knocked down by the snow, and lost in the mulch. How excited I was, one day in April, to spy a tiny sprout of that delicate gray-green emerging!
Now the shrub reaches 28 inches tall, with nine stems, most of them topped with delicate blue-purple spikes. I haven't watered it at all this year. But then, it's been a wet one. In fact, the second in a row.
I think of that bed as dry, because of the terrace and my sandy soil. But am I stuck in old ideas? Will this damp weather continue, from global warming? Last year too much rain killed my Pitcher's sage in that same bed. Will this drought-lover do better?