It gets hot in Michigan. Sometimes melt-your-face-off hot. It’s almost never a dry heat, either. Heat and humidity breed a special sort of misery for us here. Working outside in the sun you feel your skin burning at 90–95 degrees at the same time you’re swimming through air with 95–100% humidity (yes 100% humidity and it’s not raining!). So you can imagine an alpine plant growing here, whining and complaining, attracting every airborne fungus and disease known to exist. Enter artificial shade.
I understand the premise that artificiality and rock gardens don’t go together, but Farrer is dead. Rock gardens in the countless ways they are being constructed are all artificial constructions, from Harland Hand’s hillside garden overlooking San Francisco, built with every kind of rock, brick and cement, to Lola Lloyd Horwitz’s small Brooklyn, New York, garden that partially uses chimney flues. On this basis, I think what I’ve done here isn’t too bad looking and could fit into a liberal idea of a rock garden. And most of all it allows me to grow some plants that I heretofore haven’t been able to grow.
I love shortias (I know, I know; that’s like saying I love chocolate) and I was prepared to do anything short of burying a refrigerator in the ground to grow them. My friend found that growing shortias in a sandstone trough buried in the ground in the shade
of a pine tree was enough protection from the sun and tree roots to grow them. Not in my gravel pit, though. So, I hooked up a shade cloth to my house on the northwest side and it worked – almost. It wasn’t quite big enough, and at certain times of the day it still allowed direct sun to touch the princess-like leaves – they recoiled and sulked but they lived. I used the shade cloth for several years but it was a nuisance.
I had to take it down before the snow and put it up before the scorching sun arrived sometime in March or April or May. I needed permanence.
I built a ... well, what to call it? A lath house? It is simply a roof built of 2 × 8-inch rafters with 1 × 11⁄2-inch strips of wood (laths) nailed to the tops of the rafters with 1-inch or so spaces between them. This allows rain and snow and some light to get through. It’s supported by posts in the ground, and there are no sides. Underneath the lath-house roof is a 4 foot × 15 foot × 3 foot-tall raised bed made of 4 × 6-inch landscape timbers. I filled it with a mixture of 2⁄3 sand from my land and 1⁄3 sphagnum peat moss.
The sand here is acidic which allows ericaceous plants to grow pretty well. If you don’t have acid sand it would be worth trying to locate some. It seems many shade plants, although not all, like or require acidity. Oftentimes your local pit operator will know what the pH of his sand is. What I have been taught is, at least here in Michigan, the deeper the sand is in the ground the less acid it will be, the top 8–12 inches of undisturbed sand being the most acid. Another option is pure silica sand, it is also acid. Silica sand is the sand used for sandblasting, and unfortunately real silica sand is getting hard to locate.
In Michigan, people mine peat from our swamps and fens, they call it sedge peat. The pH of sedge peat is quite variable, often alkaline and not generally recommended for ericaceous plants.
I also fashioned a watering system using rain from the roof of the house. I ran the downspout into a 4-inch plastic pipe with 1⁄4-inch holes drilled into it and suspended it slightly above the top edge of the bed. The bed stays moist unless it doesn’t rain for
a few weeks – a regular occurrence. Then the hose fills in nicely. I have wellwater with a pH of around 7 and this hasn’t had any ill effects on the ericaceous plants. My first well had water with a pH of 8.2. I killed many ericaceous plants until I got a pH tester and a hose-on adapter. The pH tester is electronic, you simply dip it in your water and it spits out a digital reading. The hose-on is a brass fitting that threads onto the outside sillcock. It has a rubber hose that dips into a bucket of water with fertilizer diluted in the bucket and siphons out the dilute fertilize or, in my case, battery acid. I found that an old-fashioned film canister full of battery acid in a 5-gallon bucket of water would take my 8.2 pH water down to around 6.
Opposite the raised bed, against the house, under the lath roof there is a section of garden about 7 x 16 feet that’s not raised. The sand here was heavily fortified with leaf mold, creating a very nice woodsy soil.
I grow an assortment of shade plants including Carex fraseriana (Cymophyllus fraserianus), Podophyllum hexandrum, hepaticas, trilliums, Anemonopsis macrophylla, anemonellas, Stewartia ovata and, yes, in a couple of buried sandstone troughs I grow Shortia uniflora ‘Grandiflora Rosea,’ S. soldanelloides var. magna, S. galacifolia, and S. galacifolia x S. uniflora ‘Leona.’ In the raised bed I planted gentians, primulas, dodecatheons and Linnaea borealis. The Linnaea was interesting; I couldn’t grow it before, now I have to clip it to keep it from smothering the other plants in the bed. I also have been successful with Epigaea repens and Polygala paucifolia, Michigan native plants that were giving me fits to grow before. I also did a minor experiment on one end of the raised bed. It gets more sun on the west end so I buried sandstone like a Czech-style rock garden and planted that space with many plants that usually insist on full sun or at least more than they get there. In those spaces between the stones (1–2 inches wide) I put Asperula, Daphne, Erigeron, Gentiana, Veronica, Fritillaria and others. It’s remarkable to me how well these plants are doing in this shady spot.
In the shade of trees, which I have plenty of, I grow the usual subjects of epimediums, trilliums, rhododendrons, and the like, and they do fine. The touchier plants can struggle in this competitive environment. I find the problem to be tree roots. They rob the soil of too much of the moisture and nutrients.
If you don’t have the wherewithal to build a lath house but still want to grow some of the touchier plants, a less expensive way is to bury a swimming pool. No, not a 20-foot circular above-ground pool, although that would be very useful; just use a 4–5-foot kiddie pool. Bury it where you want it and deep enough so you don’t see the blue edges. Fill
the pool with your choice of soil mix and mound up soil towards the middle. This ensures that you’re not creating a bog, unless of course you want a bog, but that’s another story. I don’t poke any holes in the pool. We get around 35–40 inches of rain a year and I don’t have a problem with it being too wet. You can also use this strategy to grow other types of intransigent plants by changing the soil composition or pH, or to just confuse your children about what a pool is for.
I am sure other people have other strategies to grow the plants they like so don’t give up until you have killed a bushel of plants, or your partner says the kids are hungry.