As I stated in my first post, woodland soil is very different from the earth found around our homes. Sensitive woodland species that many of us would love to grow in our shaded gardens, like Trillium or Blue Cohosh, won't do well without serious amending (tips, later). Before I address the challenge of yard soil and sensitive woodland species, I'd like to give a few short answers to those who wish to plant around their home.
If we take soil quality out of the equation, for part-shade to part-sun, up against a home, your best bet is to selectively choose savanna or prairie species. No problem —we love prairie flowers ๐ฅฐ! Prairie species work best on southern, eastern or western exposures with five or more hours of sun, and savanna species can work with as little as two or three hours over the course of a summer day. Soil should be relatively lean (not rich) and well-draining (to go into depth on this will require a future post).
"But what about shade cast by a wall, or deep house eaves, or our new six foot fence, grandma's lilac hedge, and even grandpa’s Norway Maple ๐ซ?"
These are all quite different scenarios where shade is a common factor. Behind a fence or shrub hedge where you find consistently dappled sun, or early or late direct sun, you can try semi-shade savanna species like Columbine, Zig Zag Goldenrod, Wild Strawberry, False Solomon's Seal and others. If you need a longer list tailored to your site, I am available for consulting. Again, this very short list of recommendations, above, is made apart from the question of soil quality. The most successful native plant gardeners are those who understand the composition of the soil found in their yards.
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| Dry, savanna garden: shaded by large pine & garage from southeast to west, and eaves. |
Fully-shaded beds up against north-facing house walls can be inhospitable to many plants, including woodland species. The shade on the north side of a house can be exceptionally dark -darker than a forest! Further, house eaves, or even trees planted too close to the home, can block rainfall leading to exceptionally dry soil near the house. On the other hand, north-side soil can also remain consistently cool, damp, compacted and infertile. If house eaves drip, that can further compact soil and splash away added topsoil or compost.
Compacted soil near the home, or anywhere in the yard, is a problem gardeners inherit from the home building process. The excavation of the home site and foundation, at the time of construction, leaves subsoil and substratum on the surface. These were scraped and dug, piled high, and then spread around the yard and pushed against the newly built foundation. Heavy machinery compacts that subsoil, which is often a dense, sometimes chalky, silt-clay.
Contractors often finish a site with driveways, patios or sidewalks (aka hardscaping) near the house, increasing poor soil and compaction near the home. When all is completed, topsoil reserved from the original site grading, or brought in from elsewhere, is spread thinly around the property. This establishes the convoluted O and A horizons (see image, below) found in most small yards. If you want to learn more about soil compaction and how to mitigate it, check out this page from the MN Pollution Control Agency.
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| Original: Wilsonbiggs Vector: EssensStrassen, CC BY-SA 4.0 , via Wikimedia Commons |
It is entirely possible that your home was built in a region with a different subsoil profile —maybe sand or a mix of silt, sand and gravel. This is less common, but is possible in glaciated zones across North America, especially where glaciers terminated and retreated ages ago. In these cases you may find your property has different challenges, although no less problematic for sensitive woodland species. If your entire property is larger than the average city lot (1/20 to 1/10 acre) or suburban lot (1/10 to 1/4 acre), you may find intact native soil horizons in parts of your property. However, near the house, especially one with a basement, you are unlikely to find native soil, or even good garden soil if it hasn't been modified by years of amending.
"Okay, so that's mostly near the house, but what about the barren spot under the Norway Maple —way out in the yard. It used to be lawn. Why can't I grow woodland plants there? ๐ค"
To reiterate —away
from the home, native soil horizons may still be intact. However, where home lots are small or extensive grading was done, it is likely that subsoil was spread and topsoil added, then a carpet of sod was laid. When they planted the non-native Norway Maple, a common practice in many regions across the US, it was but 10 feet tall. As the tree grew tall and wide in the open sun, its long, low, and leafy branches shaded out the bluegrass lawn.
"So the Norway Maple killed my lawn? ๐ค"
In part, yes. Yards and streets have individual tree specimens —each with a large canopy much wider than those found in a sunlight-competitive environment like a forest. While there are shade and drought-tolerant grass species, U.S. lawns tend to be a mix of sun and water-loving bluegrass and rye. Because of ample sun, the Norway Maple maintained and lengthened its lower branches, creating an ever-widening ring of shaded ground beneath it, making the lawn stressed by low sunlight. However, the lawn and maple, together, made for a feedback loop that spelled the end for the lawn and nearly anything else that you may try to grow under that maple.
๐ณ "Isn't there anything I can plant there?"
Not much. The tree's sunlight-driven horizontal growth, its exposure to shallow lawn irrigation, constant runoff, low organic matter due to raked leaves, already compacted soil made worse by foot traffic,
and lawn fertilizers strewn about pushed the Norway Maple to grow longer, larger lateral roots at or near the soil surface. These same conditions forced it to develop a dense network of surface feeder roots across an area even wider than its
canopy. The conditions created by this combination of lawn and tree are nearly inhospitable to growing other plants, native or not. Where these conditions exist, landscapers and gardeners chop and till feeder roots, add fresh soil, each year, just to grow shade-loving annuals like impatiens. Irrigation is a necessity to grow anything other than the maple because its feeder roots suck dry all moisture that makes it through its dense canopy.
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| Trees eat grass for lunch and "Keep Off The Grass" signs for dinner. ©Meuschke 2010 |
Trees are the dominant species, after all, so they get first dibs. As you can see, in this case scenario, there is little you can do, without constant work and amending, to grow woodland plants under that tree. You could, of course, cut down the Norway Maple. Not to pick on this particular species —in a maple forest much less grows in its dark understory compared to an oak woods or mixed deciduous forest. A lawn environment, combined with any number of tree species planted as individual specimens, can create a set of problems similar to that described above.
"Wait,
it can’t be this way everywhere and I've seen yards with trees and lush gardens!☝️๐คจ"
Right. This is a
generalization. Every yard has its own set of unique conditions to be understood before setting out to plant. Variables from construction methods to
pre-development land use to garden and arborist practices over decades can change outcomes. However, the concepts above are
sound.
In this series of three posts I set out to address growing sensitive woodland plants in a home garden, but this niche, especially when it comes to the woodland ephemeral species, can be challenging. The quantity of variables appears to be one reason for so much failure, but the most important factor is you —the gardener. In part 3, I will reveal the simplest thing gardeners can do to sustain sensitive woodland species in their shade gardens.
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