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Gardening Study Urban Greening

by Tracey Williams, Designer and horticul­turist, and owner of Greensleeves Design
March 20, 2020

                                                                            GARDENING STUDY

                                                                             URBAN GREENING


This new century has been an excit­ing time for those of us who work in the field of green infrastructure and also for those whose lives and visits to our cities have been positively affected by ur­ban greening. Green-living spaces, urban parks, community and school gardens, have been power-seeded throughout the urban landscape, allowing residents to relax, cultivate and farm their somewhat finite but wonderfully accessible outdoor allotments. Green roofs have evolved from our envious glances across the European continent to include a bevy of dynamic and inspiring projects all across this country. 

A more natural hydrological movement of storm water is being mimicked by installing pervious asphalt and permeable pavers to minimize runoff. Downspout disconnections are re-directing rain into barrels, tanks, and collection ponds to use in the landscape. Infiltration trenches, tree street planters, and vegetated filter strips are beautifying our urban landscapes. Equally important is floodplain restoration and preservation where existing buffer zones are planted and managed to preserve the hydrological “right of way.”

Beekeepers are squeezing their hives onto blighted city lots and garden rooftops, aiding the pioneers of urban agriculture in providing city dwellers with access to fresh food, increasingly minimizing food deserts in neighborhoods depleted of fresh, organic produce. Green walls, and the ever-flexible techniques of green façading, have brought life to the previously underutilized sides of buildings, bridges, and highway overpasses and offer degrees of shading and cooling previously unrealized.

The benefits of green infrastructure are best achieved through the additive effect of varied projects.

Garden Drip Irrigation

Drip irrigation and vertical planter of the author’s design allow for a colorful and dynamic garden in a very small footprint, perfect for city living.

Garden Green Wall

 This green wall, in a city rooftop garden of the author’s design, features a wide variety of edible plants for easy picking. Lettuces, herbs, and small strawberries are enchant­ing when viewed at eye-level. Drip irrigation supplies consistent moisture and the free-draining growing medium encourages the winter-hardiness of many species.

What is so particularly exciting about urban greening is that, like drops of water accumulating in a rain barrel, together many smaller projects add up to

create a more livable and green city. We all have a part to play, and in lots of little ways we can crack open the impervious horizon­tal asphalt of our cities and allow green to spring forth. We can add soil to rooftops, peel away road mediums and sidewalks to allow water to slowly re-enter the groundwa­ter supply through the filter of living plants and bacterium, without forcefully churning into our combined sewers, taking with it all sorts of pollutants and chemicals.

Plants are opportunistic and surprisingly rugged, and we only have to make a few concessions in the hardscape of our city environment for them to flourish. Needing only the substrate to grow it, the water and nutrition to allow them to thrive and their selection for the particularly challenging environment of the city, they reward us many times over. From cooling and cleaning the air, to reducing energy costs, to sup­porting biodiversity in our environment, in addition to the somewhat intangible perks, which include a wide variety of quality of and health benefits, including an en­hanced sense of community and a vigorous economy.

With more than 54 percent of the world’s population currently living in cities, with that number projected to increase to 66 percent by 2050 (United Nations Dept. of Economic and Social Affairs), many already appreci­ate and understand the importance of this interconnectedness with our natural world. Nature does not stop at the city’s edge but must be both encouraged to infiltrate through designed and managed greening projects, and PRESERVED where it has already been established.

Tips for Urban Plantings

• Like our more traditional garden, it all starts with the soil. This is not mere dirt, but rather a crucial element in building a healthy ecosystem. By understanding the interconnected web of physiochemical and biological components of healthy soil and enhancing the complicated interactions

between fungi, bacteria, nematodes, and protozoa, along with oxygen, carbon, hydro­gen, and the minerals that support the health of plant life, a community of plants can be supported with less inputs, fertilizer and labor. The incorporation of large amounts of compost increases the capacity of the soil to capture water during a rain event and slowly release it, like a sponge, back to the plants during drier periods. The use of mulches that are natural, undyed, sustainably harvested, and applied minimally and away from the trunks of urban trees will prevent weed ger­mination, regulate soil temperatures, retain moisture, and, as they break down, improve the tilth of the soil.

• Engineered or structured soil can be particularly useful to combat the com­mon problem of compacted urban soil. The benefits of these growing mediums, many especially designed for green roofs, may vault down to ground level, and this addi­tion of expanded shale in many urban and

residential projects may be of particular im­portance, especially where one encounters areas of heavy clay and compaction, where it promotes drainage and a healthy oxygen exchange.

Gardne Green Wall in Autumn

The same green wall in autumn when annuals mixed in with economical perennials reduce maintenance and enhance a beautiful spot to enjoy the last warm days of the season. These urban green spaces offer a respite from the demands and stresses of city living.

•When planting on balconies and in areas where planters are required, careful at­tention must be paid to their size and shape. The larger the better, as the increased soil volume will add thermal insulation both in summer and winter and also offer better moisture regulation. Square or rectangular planters offer more stability than those with narrower bases, and all should be securely fastened to prevent toppling, or worse, becoming airborne. The turbulence and velocity of the wind may be unpredictable in the city as it torrents, gusts, and uplifts between buildings. Plants, too, should be secure in their pots, and gravel mulch may prevent soil from being scoured out of plant­ers by the wind. The material of the planter is also an important consideration, as their weight, ability to withstand harsh UV light, and extreme temperature fluctuations will prolong their lifespan and usefulness. Sheets of insulation board may be cut to fit along the planter sides to further insulate against heat and cold. 

Garden Autumn Colors

 The autumn colors of native and well-adapted species.

Weight consider­ations are obviously one of the most crucial factors when it comes to rooftop and balcony gardens. If there is any doubt what­soever about the load al­lowances, a consultation with a structural engineer is a sound investment. The more elaborate the project, the more complicated the issues with regard to load and water­proofing but, as experience and training is catching up to demand, there are many green-roof professionals who may be con­tracted for advice.

• The watering of plants growing on rooftops, walls, and balconies, including those at ground level, give us an opportunity to significantly conserve this increasingly valuable resource. The drying effects of the wind and the increased heat in a city can destroy a planting in a few hours. A well-designed watering system will ensure the success of the garden. Typically, projects factor in a drip-irrigation system, which need not be complicated or expensive. Many self-irrigating planters systems (or SIPS) are available to purchase or make and the In­ternet is awash with plans for the do-it-yourselfer. 

Salvia and Viburnam around table

Salvia ‘Wendy’s Wish,’ Viburnam ‘Winterthur,’ and Nepeta abound with late-season blooms and berries and offer a valuable resource for pollinators in the city.

• A factor often not realized by the novice city gardener is the extent to which sun and shade patterns may change over the course of a year. With tall build­ings looming overhead, or the sun dropping below a nearby apartment in winter, the light corridors are extremely variable and must be considered and planted accordingly.

• Aim to eliminate areas of costly maintenance, such as turf. Mass large, dense sweeps of perennials to behave as an alternative to lawn. In our Zone 6 climate, Chasmanthium latifolium, a native with a reputation as a bit of a thug, but easily contained by the asphalt restraints typical in the city, can be successfully used en masse to eliminate the need to fertilize, mow, and spray a traditional lawn. Other options might include many of the selections in the beauti­ful Carex genus (many suited for shade but some also adapted to the sun), Sporobolus heterolepis (Prairie Dropseed) and even ubiquitous Liriope.

• Plant densely and with the inten­tion of covering most, if not all, of your soil. This density prevents weed infiltration into the gaps in the plantings, requires less mulch and other inputs, shades the soil, and prevents compaction from  foot traffic and driving rain.

Native switch grass an native bamboo

Native switch-grass (Panicum ‘Heavy Metal’) and our native bamboo (Arundinaria gigantea) add a special winter-interest to the garden, six-stories up, and overlooking the Ohio River.

• Include native species, which are well adapted to varying pH, nutrition, and soil conditions and typically boast deep and extensive root systems, which support the plant through typical periods of drought and the extremes of an urban environment. Be willing to experiment with rambunctious and riotous plantings that might offer blooms for pollinators over a long season. Don’t dis­count the efficacy of self-seeding annuals, such as Cosmos ‘Bright Lights, Verbena bonariensis, Browallia, and Celosia and al­low their seed heads to remain through the winter to self-propagate and feed the birds, who will appreciate the bounty.

Selfirrigating planter

SIPS, or selfirrigated planter systems, are engineered to slowing release water from the bottom of the planter, reducing watering requirements and eliminating messy runoff.

• Trees offer an incredible opportu­nity to combat climate change in our cities by absorbing carbon dioxide and other pollutants, releasing oxygen, cooling the hot corridors of our cities through shading and tran­spiration, preventing soil erosion, reducing energy demands, and creating habitat and providing food for many species of birds and animals. While many situations require that we plant trees that don’t drop much litter, there are many opportunities in our cities, as well as our residential gardens, to plants trees to sustain wildlife. Take, for example, an oak tree, which studies suggest can support more than 500 different species. While this may not be suitable for high-traffic areas, there are typically many office and recreational parks, highway-overpass green spaces, and schools where the inclusion of these hefty, long-lived na­tive trees are possible. Let’s hear it for the oaks, catalpas, hackberries, coffee trees, beeches, and butternuts!

• In contrast, other applications demand new tree species bred with fastigiated and columnar shapes, or those that have been bred to be fruitless, allowing for ef­fective street-side plantings. Careful selections of smaller trees under power lines will prevent future unwanted pruning, bad for both the tree and maintenance costs. Most cities offer tree lists of desirable urban selections, and following their recommendations will allow for excellent success in this endeavor.  

Dove in planter


Garden spider on plants

This green wall and planter garden have played host to a wide-variety of birds, insects and arachnids.  Managed with organic practices, a balance has been achieved and praying mantis, ladybugs and many birds easily dispose of undesirable and destructive insects.

• The importance of urban ecology is in­creasingly being under­stood and supported as the plight of declining spe­cies demands that we include our cities in their habitat to encourage their diversity and genetic vari­ety. For an urban corridor to be effective, it must be dense enough, and close enough together, for the mammals, birds, bats, butterflies, insects, arachnids, and amphibians to traverse through them. In the urban environment, the vitality of this network enhances our lives in many ways, and as our urban population becomes denser, so should we balance our volumetric greening accordingly. We all have a role to play in creating livable cities and, as we strive to find balance in the web or our urban ecology, we have the opportunity to greatly enhance the quality of our lives and that of ALL of our neighbors.


Tracey Williams, Designer and horticul­turist, and owner of Greensleeves Design. Specializing in urban and residential gar­dens

Articles and photo reprinted with permission by The National Gardner, Winter 2016.



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