When you fly over Buffalo you see a green canopy. We have trees, even though the 2006 storm stole too many. When you walk around Buffalo – the plan for many thousands this weekend during Garden Walk Buffalo – you will see gardens under, around, shaded by, influenced by, climbing on and hanging from trees. Many of our trees are more than 150 years old with 2-foot diameters and canopies wider than 50 feet. Most Buffalo gardeners must garden in some shade.
Gardening in shade is not necessarily a bad thing. It is often more comfortable and healthier than gardening in full, skin-damaging, dehydrating sunshine. But gardening in shade among trees presents serious challenges: You have to adjust what plants you grow and how you grow them – while trying to have a high-performance, fully flowering garden. See how our talented Buffalo gardeners do it.
Trouble with tree roots
A planting bed in the shade of a building is a wonderful thing. You can prepare the soil, choose from the lists of shade-tolerant plants and plant them. Water properly (for their individual needs), and the plants will grow to be all they can be. Begonias, New Guinea impatiens, fuchsias and Caladium will be glorious by mid-summer. Perennials like Lobelia, Bergenia, Pulmonaria, Hakonecloa macra and Tradescantias, astilbes and hostas will be attractive the first year and fantastic by the third year.
The same plants in a tree-root-filled space cannot perform with the same aplomb. Established tree roots can suck up moisture and nutrients much faster than a new plant’s feeble root system. Tree roots quickly grow into the new plant’s well-prepared hole and steal the water. Consider Astilbe as evidence: Many of you have bought astilbes, promoted as “shade plants,” and like me, you have been disappointed – they just sat there. Finally I got it: We call astilbes “shade-preferring” mainly because they need a lot of water and dry out too quickly in the sun. With a lot of water they grow well in full sun! Now imagine how much more quickly they dry out with tree root competition. Lesson: Grow astilbes where they will get lots of water, and not where they compete with tree roots. Where there are tree roots, do something different.
How to garden among roots
• Cut roots very selectively: Gardeners must make a judgment when and how much to cut tree roots to allow for gardens under trees. Cutting a lot of tree roots stresses trees (already stressed in most urban situations) and endangers their health and longevity. If you want to keep a tree healthy, do not cut across several feet of tree roots under the tree canopy, even 6 inches deep, as most tree roots are within the top 15 inches of soil and many very near the soil surface. Do not add a raised bed under the tree canopy any deeper than 4 inches, or you’ll cause compaction and limit oxygen availability for roots. You can dig specific holes for plants – the farther out from the trunk the better. Then, for the sake of the new plants, cut the roots several inches outside the planting hole.
• Add compost: Add especially generous amounts of compost to every planting hole, under and around new plants. Compost retains soil moisture and enlivens the microbial life of your soil. Garden Walk Buffalo participant Tom Halloran of Richmond Avenue attributes some of his success – a sloping front yard overflowing with flowering plants – to the compost he uses. He plants everything using lots of Bumper Crop compost, a bagged product from Coast of Maine organics that includes shellfish products and worm castings. The plants got a healthy head start and survived some droughty periods. Even his root-filled “hell strip”– Buffalo’s term for the space between sidewalks and streets – is thriving.
Other forms of organic matter work too. Stephen Bellus of Lancaster Avenue started his beds decades ago with just a couple of inches of top soil. Since then he has augmented them every year with cocoa shells and Milorganite, so that now the soil is rich and penetrable and he can transplant even large rootballs such as hostas easily.
• Sink space-holders: Sometimes called the “pot-in-pot” technique, this trick helps you avoid digging the same hole year after year to insert your Dragon Wing Begonias: Cut a hole among roots, deep and wide enough to insert a pot – say, 18 inches wide. Place a second 18-inch pot full of your chosen plant(s) in it. Switch out the insert pots during the gardening season, from bulbs in spring to mums in fall. In winter, the empty space-holding pots will heave out, so fill them with soil or rocks when they aren’t in use.
• Raised beds and containers: Buffalo’s tour gardens are a study in growing as much as possible in containers and raised beds, whether on driveways, rooftops, pool decks, second-story porches or in root-crowded gardens under trees. On Highland Avenue, Ellen Goldstein and Mitch Flynn use artfully placed pots and planters to create a feeling of flowering English borders – in spite of 50-foot trees in surrounding yards. Bellus grows mini-hostas and Heucheras in lake stone bordered beds in his tranquil, elegant and very shaded garden.
In Allentown, with generally shallow yards, most front yard gardeners contend with the roots of street trees by building raised and enclosed foundation beds. Or they choose root-tolerant, competitive groundcovers. Back gardens in Allentown, such as the North Pearl Street garden of Elizabeth Licata and Alan Bigelow, are original courtyards of homes built in the 1800s; they don’t have deep, back lawns. So Licata plants perennials, vines and Oriental lilies in brick and stone-enclosed raised beds, and crams containers with annuals and bulbs and places them where the light is available.
Gardening in shade is both science and art, and as most Buffalo gardeners will tell you: We’re all still learning.
Sally Cunningham is a garden writer, lecturer and consultant.