Planting Perennials in Stone Walls and Rock Gardens
I must confess that my first impulse to begin a garden was not an urge to connect to the earth. Instead, it was brought on by a stone wall. The wall is the foundation of an old sheep barn we had, until it caved in we had it knocked down and shoved into a giant pit in the backyard, where we burnt it.
What remained were ruins- ruins the like of which one expects to find in some European countryside, but not in ones own backyard.
Ruins really appealed to the romantic in me. I had other gardens but nothing I was passionate about –merely scattered areas where I planted flowers and bulbs because when you own a home, you’re almost expected to do a bit of gardening there. But the idea of creating a garden in the ruins really stirred something in me.
All the sensible gardening tomes strongly urge you to plant your major area close to the house – otherwise chances are good that it will be not only out of sight but also out of mind and thus neglected. Our ruins are lie about an acre away from the back door. But I was determined that we needed to create a real garden there. Which we did – The area in front of the ruined wall is now the main garden; and we created a second, raised bed opposite the ruined wall, backed with a hedge of hemlocks trimmed to shrub shape.
It has now become something else I never thought I’d have — a walled secret garden complete with gate.
Creating that garden proved addictive. I purchased more plants than there was room in the ground. And that is when I looked up. I was surprised and thrilled to realize that I hadn’t even begun to exhaust the planting possibilities in my little walled garden. Plants could and soon did – grow in the nooks and crannies of the old stone wall!
It began serendipitously. A columbine seed must have blown around and landed in a pocket of soil there. A rainy spring was ideal for germination. I was, of course, too focused on the ground to notice until I looked up one fine sunny day and saw that columbine flowering far above ground level.
That was all it took! I was soon quite certain that I could transform that wall into a solid mass of flowers.
But alas! – it’s not that simple.
If you built a wall specifically for planting, you would leave enough space between stone for large pockets of soil so that plants can develop substantial root systems. If you do that, your possibilities are, if not limitless, or at least substantially increased.
My wall was stone that had at one time been plastered over. As the plaster decayed, large holes appeared, and in the normal course of things, dirt lodged itself in those cracks. So I had soil pockets – it’s just that they were small, and didn’t hold the moisture very well. Still – with some careful plant selection I had some success.
Sempervivum is a plant with many nicknames: house leeks, hens and chicks or Live Forever ; they are succulent plants that need almost no water to survive. Better yet, they have very small root systems. In fact simply tossed into a box waiting for planting they’ve been known to take hold and grow. One year I received a huge quantity of semps – way too many, and while I planted what I could, remainder sat for over a year ignored and unplanted and kept on growing. I was sure they would grow in my wall, and I was right.
What is particularly charming is that they continually send out little chicks that frame the stones beautifully. Even nicer, as a bonus, the ones I used, normally a crimson-tipped green, became a beautiful burgundy in winter — much needed color when all you have to look at otherwise is gray stone.
Encouraged by my success I started looking at several types of sedum plants that were growing in different parts of the garden. I like sedums not only because they come in so many different and interesting foliage colors, but because they are drought-proof. Like the semps, sedums are succulents and so can live in something like a fairly dry wall. The fact that a nickname for sedum is stonecrop should have given me a hint.
Best of all, they are incredibly easy to propagate. Break off a stem and push it into the soil. And before you know it, even if you forget about it, you soon have a new plant.
So planting sedum in the wall was free. I broke off pieces of plants I already had growing around the garden; filled any promising gaps in the wall with moist soil and stuck them in. It was a happy experiment; I now have plants that are colorful all year in shades of blue, purple, red and chartreuse to name a few. They do flower, which is nice. These flowers are the only maintenance factor involved with sedum – in spring I have to go around and cut off the dried stalks and then we’re back in business.
One sedum relative that I am particularly fond of is a little plant called Orostachys chanetii which grows in little powder blue rosettes. They look like tiny blue rose buds, and look subtly beautiful against the gray of the stone wall. An altogether satisfactory experiment.
Snow in Summer
Flushed with my new-found success at wall planting I looked around for other options. Purely as an experiment I moved a bit of Cerastium tomentosum (Snow in Summer) from the garden, where it was trying to take over, to the wall. In the ground it’s a real thug, so I figured that such a strong grower might be hardy enough to at least survive in my stone wall.
It did more than live — it took hold and soon I had long cascades of silvery white streaming down the face of the wall.
In a couple cases it completely obliterated the garden plaques that my husband hung there to relieve the wall of its formerly blank look. He and I both think of this walled garden as a room. To his way of thinking, a room with walls needs pictures. And they look great — where you can see them amidst the plants. But when the snow in summer lives up to its name by covering itself in pure white flowers, that garden art can be very difficult to see. The plants need a trim every spring — I always feel a bit like I’m doing drastic barbering to an old man’s beard. So for a time the wall art regains prominence before receding in a tangle of living things again.
My success here led me to investigate several other plants that are labeled as rock garden plants. These plants require excellent drainage and often prefer dry conditions. My main concern was providing them with enough soil for them to develop good root systems. I found that I could cram a lot of moist soil into the larger holes in the wall, and so figured I may as well try to see what else would live in those larger holes and fairly dry conditions.
My most spectacular success was with purple rock cress, Arabis caucasica. It has spread like a bouquet across and down the stones, and every spring covers itself in purple-y pink flowers that arrive along with the earliest of the bulbs. I suspect that it is the warmth of the sun radiating from the stones that urges it to flower so soon, because it isn’t such an early riser in the garden itself.
There is also a blue flowering plant growing in my wall – but I don’t remember planting it, and am not exactly sure what it is. I assume it’s a form of Aubrieta, a type of rock cress that is related to the pink Arabis, since it blooms at the same time and looks very similar. The fact that both are called “rock” cress is what inspired me to try them in the wall, and it has most definitely been a success there.
Creeping phlox (Phlox subulata ‘Candystripe’) is the final entrée on the menu of plants I have deliberately and successfully grown in my walls. It’s a common groundcover for spring around here, often planted in checkerboard patterns in front yards further out in the country, rather like the bedding schemes so popular in the Victorian era. Most of the time I use it as an edging plant — but it appears equally content with its roots stuffed into the wall.
Most of my flowering perennials do their star turns in spring, which is most welcome. The succulents take over after that, adding color to the soft gray wall.
But the wall appears to have become a seductress, and is attracting plants that I would never have expected to take up residence in the conditions it can provide. Just this week I noticed a buddleia that must be at least a year old (usually hidden behind a purple smoke tree.) That has to go, as the damage it could do the wall as it matures could be dire. Ditto for the greater celandine and oxalis that seem determined to overrun every plantable place in the yard. But I’m leaving the echinacea that I see sprouting, mostly out of curiosity.
Hey — unless you give it a try, you’ll never know what you can grow where. And if the plants want to volunteer to help with my experiments — let them go for it.
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