------------------------- U of MN Extension Service FO-06709

Sustainability in Urban Ecosystems*

Vera Krischik and Kathryn J. Bevacqua


©  2005  Regents of the University of Minnesota. All rights reserved.

* This publication may serve as a guide to the video, Sustainability in Urban Ecosystems

A Sustainable Landscape

A sustainable landscape is defined as a site where native and introduced plants are well suited to the existing light, moisture, and soil conditions, and require low inputs of labor, fertilizers, herbicides, insecticides, and fungicides to thrive. A sustainable landscape preserves and protects nature’s balance, while providing aesthetic pleasure.

The gardener’s objectives differ from the agricultural model driven by yield and profits which justifies the use of fertilizers, herbicides, insecticides, and fungicides. Sustainable management promotes tactics that recycle nutrients to foster an ecological balance. Other strategies lower the use of broad spectrum pesticides to permit the natural control of damaging insect populations by insect predators and parasitoids. Finally, sustainable management encourages diverse and alternative landscapes that require lower long-term maintenance.

Figure 1

Landscape managers and gardeners generally want a landscape that is easy to maintain and looks good. Sustainable landscaping is a common-sense approach to obtaining both goals. Properly designing or even redesigning a landscape is the first step toward lowering maintenance. An important part of Plant Health Care (PHC) practices is determining how an area is to be used and selecting plants appropriate for both that purpose and for the site. Once a good design is in place, other PHC practices come into play: composting yard waste, encouraging biodiversity, and implementing Integrated Pest Management or IPM. All these strategies are part of responsible urban landscape stewardship.

Whether you are planting a garden, managing turf, developing a parkland, or landscaping a parking lot, your management practices affect everyone. The decisions you make affect water quality, waste disposal, and the survival of all forms of wildlife.

When looking at alternative landscape practices, think in terms of management rather than control. Work with nature to restore the ecosystem balance by improving soil and site conditions. Since problems can’t be eradicated, begin by accepting some imperfections, understanding the problems, and using creative management strategies to restore environmental health. As a result you’ll have a more harmonious environment and more leisure time to enjoy it.

Turf Care

Selecting the right plant for the right place is just as important for a lawn as it is for any plant in the urban landscape. For example, a thick bluegrass lawn grows best in sun. For shade, select a variety of fine-leaf fescues to plant. The recommended height for lawns is 2.5"-3"; mow shady lawns an additional one-half to one inch higher. This height provides more surface area for the leaf blades, allowing better use of the available light for photosynthesis. In addition, longer leaf blades are supported by a larger root system, permitting grass to better cope with summer drought. See Table 1 for grass varieties and their recommended mowing heights.

Table 1. Recommended Grasses and Mowing Heights for Low Maintenance Turf

SiteGrass VarietyMowing Height
Residential lawn in sun60-75% Kentucky bluegrass (2 different varieties)
25-40% fine fescue (1 or 2 different varieties)
Residential lawn in shade60% fine fescue
40% shade tolerant Kentucky bluegrass
Recreational/athletic fields50% perennial ryegrass
50% Kentucky bluegrass

For more information, see Turfgrass Management for Protecting Surface Water Quality, MN Extension publication BU-5726.

No lawn should be cut too short; close mowing stresses the turf, depletes its food reserves, and makes it susceptible to drought stress. Remove no more than one-third of the blade height at one time. Frequent mowing allows you to leave the clippings on the lawn where they quickly decompose and return nutrients to the soil. Leaving clippings on all season is the equivalent of applying one fertilizer application, but with less effort, less money, and less harm to the environment. Keeping mower blades sharp reduces water loss and prevents disease organisms from entering the leaf blade.

For best results, fertilize your turf when grass is actively growing. Minnesota’s cool season grasses grow in spring and fall. If you only fertilize once, do it in early September when the plants are storing food reserves for winter. If you fertilize twice, it is still best to do both in the fall: mid-August to Labor Day and late October, in the Twin Cities area.

Turf needs one inch of water a week (combination of rain and irrigation) to grow well; sandy soils need an additional one-half inch. When supplemental watering is necessary, adding one-half inch of water at a time ensures sufficient water to the root system, no matter what the soil type.

Since storm sewers are direct pipelines to our rivers, lakes, and wetlands, we need to be careful about what enters them. Keep grass clippings off hard surfaces, where they may wash down storm sewers and add unnecessary nutrients to our water supply. Rake leaves off sidewalks and streets to prevent them from washing away.
Keep fertilizer on the grass and off hard surfaces.

A drop spreader allows better control of fertilizer granules.

A healthy turf is the best defense against weeds, but when weeds do need to be treated, spot spraying minimizes your exposure and the environment’s exposure to chemicals.

Design your landscape to reduce maintenance. For example, where turf is not used for recreational purposes, consider alternative landscapes. For shady areas where grass does not grow well, plant ground covers such as lamium (Lamium maculatum), perennial vinca (Vinca minor), goutweed (Aegopodium podagraria), lily of the valley (Convallaria majalis), or pachysandra, (Pachysandra terminalis). Taller plants such as woodland wildflowers, hostas, and ferns also do well in a low maintenance shade garden.

For sunny natural areas, create a prairie garden with hardy ornamental grasses and wildflowers. In any landscape, plant shrubs to screen out unwanted views, to create restful outdoor "rooms", and to provide food and cover for birds.

Designed properly, alternative landscapes require less long-term maintenance, increase plant diversity, and attract songbirds and butterflies. Such landscapes also provide places to rest and relax in privacy.

Tree Care

Carefully select the right tree for the right place. Start by having your soil tested to determine pH (the relative acidity or alkalinity of the soil). Not only is this factor critical to plant health, it is very difficult to change if the pH is too high. Then consider the tree’s natural environment (hardwood forest, oak savanna, wet areas, etc.) and determine whether similar conditions exist in your urban landscape. In forests, for example, leaf litter returns carbon, nitrogen, and phosphorus to the soils. Leaf litter and woodland plants shade tree roots. The paper birch, native to such an environment, will be stressed when placed on a hot, dry lawn, competing with grass for nutrients and water. Instead, plant it where it will receive some relief from the sun, in slightly acidic soil, and use an organic mulch over the root area.

In the urban landscape, trees face many stresses—low soil volume, poorly drained soils, lack of water, de-icing salts, damage from street improvements.

Stressed trees typically show crown dieback, thin foliage, waterspouts, and are more susceptible to disease and insect attacks. Damaged or constricted roots affect the tree’s stability, making it a hazard. During the landscape development process, improve the site conditions as much as possible and then select trees that can best tolerate urban stress.

Snowy Minnesota winters require the use of de-icing salts which can severely affect a tree’s growth. An obvious symptom of salt spray is witches’-brooming—a proliferation of shoots with short internodes. A less obvious symptom is a slow decline in health. Whether you are planting a tree near a busy road, planning your city’s boulevard trees, or designing a parking lot, select trees tolerant of salt (Table 2). Eliminate the use of salt by substituting sand or reduce its impact by mixing sand with salt. For high-risk or high-use areas, alternatives to salt (sodium chloride) include calcium chloride or calcium magnesium acetate.

Table 2. Trees Tolerant of Salt Spray* and Runoff

Acer platanoides (Norway Maple)
Elaeagnus angustifolia (Russian Olive)
Fraxinus americana (White Ash)
Gleditsia triacanthos (Honey Locust)
Picea glauca densata (Black Hills Spruce)
Syringa reticulata (Japanese Tree Lilac)

*Most severe damage occurs within 60 feet of a road.

From Minimizing De-Icing Salt Injury to Trees, MN Extension publication FO-1413.

For landscape managers, parking areas pose special challenges. Very often surplus construction debris is dumped into the planting pit—not a very good planting medium. A good planting pit will have sufficient soil volume for good root development, adequate irrigation, and good drainage. Table 3 shows the volume of suitable soil (well drained, not compacted) required to sustain a tree in a planting pit 2.5 ft. deep. Also, because the hard surface of the parking area radiates intense heat, plant a ground cover to help cool plant roots.

New housing construction does not have to destroy the landscape. Preserve natural areas with diverse trees, shrubs, and plants around the perimeter of a new development. Protect the natural soils of the area from removal and compaction.

Once the home or development is constructed, then reforest the site. Reforestation should take into account how the landscape will be used, such as areas for recreation, shade, privacy, screening, and erosion control. Include a variety of trees and shrubs selected for the specific site’s growing conditions.

Table 3. Planting Pit Dimensions
Mature Tree Size Required soil volume
Spread of CrownDiameter of trunk (measured 4.5" up from base)
140 sq. ft. 4"200 cubic ft.
320 sq. ft. 8"400 cubic ft.
480 sq. ft. 12"700 cubic ft.
640 sq. ft. 16"1000 cubic ft.
900 sq. ft. 20"1200 cubic ft.
1200 sq. ft. 24"1500 cubic ft.

Adapted from James Urban, "Bringing Order to the Technical Dysfunction within the Urban Forest," Journal of Arboriculture 18(2): March 1992, p. 89.


State laws prohibit the disposal of yard waste as trash so gardeners have two options: deliver yard waste to a community compost site or compost it in the backyard. Backyard composting is an easy way for anyone to recreate the natural recycling of organic matter, while at the same time disposing of yard wastes. Compost incorporated into the soil as an amendment improves soil texture, increases earthworm activity, and adds microorganisms beneficial to plant growth. Since compost adds very little nutrient value to the soil, plants will still need to be fertilized. Used as a mulch, several inches of compost will keep plant roots cool and moist and will discourage weeds.

A variety of structures can be used to contain the composting material, but the ideal size should be 3’ x 3’ x 3’ or more. Any organic matter can be composted: fruit and vegetable waste, grass clippings, leaves, small twigs, etc. Do not add meat, grease, eggs, or dairy products (which attract rodents) or add animal feces (which may contain diseases). To keep the compost pile at the optimum temperature for decomposition (130° -160°), turn the pile frequently and keep it slightly damp. A well-maintained compost pile will not have a foul odor. Such a pile will be ready to use in 2-4 months; a neglected pile will take a year or longer.

To dispose of larger branches, check with your city recycling coordinator to determine the maximum branch size they will accept at the city compost. Branches can be chipped or shredded to use as mulch around existing trees and shrubs. Any wood properly dried for one year can be used for firewood, but municipalities may have special ordinances for elm and oak. Elm and red oak provide breeding places for insect species that carry Dutch elm disease and oak wilt. The disposal of elm and red oak wood may be regulated. Check with your municipality on how to dispose of diseased wood. In general, elm and red oak wood must be debarked, chipped, or buried.

Integrated Pest Management

Integrated Pest Management, or IPM, is the practice of using a variety of cultural, biological, and chemical techniques to reduce pest problems. One goal of IPM is to reduce any harmful impact chemicals may have on the environment—wildlife, soil, and water quality. IPM methods include proper plant selection, biorational and biological pest controls, using traps for monitoring insect populations, regularly examining plant materials for signs of trouble (scouting), and the judicious use of chemical pesticides.

A plant correctly matched to its site is healthier and therefore less prone to insect and disease attack. Know and meet the cultural requirements of any plants. Once you have decided on a particular plant, investigate the characteristics of various cultivars. Much research has been done on plant resistance to pests. Plants can be bred with inherent chemical or growth attributes that make them unattractive to insect feeding or resistant to diseases. For example, honeysuckle witches’-broom aphid feeding, a common problem with older honeysuckle cultivars, results in branch tips with a mass of shoots—at first, merely unattractive, but eventually weakening the entire shrub. Newer cultivars have been bred that are resistant to aphid feeding. Many common plant diseases will cause defoliation which will stress the plant over time, reducing its vigor and winter hardiness. For example, select rose cultivars that are resistant to black spot (Diplocarpon rosae), an important rose disease, and select crab apple cultivars that are resistant to apple scab (Venturia inaequalis), a common problem in Minnesota.

Use environmentally sound controls, such as horticultural oils and soaps, which break down quickly in the environment. Bacteria (e.g. the commonly available Bt formulations), fungi, and nematodes reduce insect populations and are generally referred to as a biorational approach. Controls such as insect parasitoids (e.g. beneficial wasps that lay their eggs on harmful insects, thereby parasitizing them) and predators (such as lady beetles and lacewings) are generally referred to as a biological control. These biological controls are naturally found in the environment, but the widespread use of insecticides kills them. By limiting the use of insecticides and incorporating a variety of plants in the landscape to attract a wide range of insects, these beneficial insects can thrive, keeping harmful pests in check.

Figure 2

Beneficial insect: An adult lacewing

Two other IPM methods—traps and scouting—are excellent ways to limit pesticide use. Insect traps can be used to monitor insect populations before they build up to harmful thresholds. For instance, an apple maggot red ball trap at eye level on the south side of each tree indicates when the apple maggot fly (Rhagoletis pomonella) is active and at potentially damaging numbers (i.e. five flies trapped in one week after July 1). In small orchards, five traps for an average-sized standard tree can actually control or “trap out” apple maggots, so that insecticides need not be used. Also traps alert you to the presence of insects, allow you to determine when thresholds have been reached, and serve as monitoring devices.

Scouting, or the routine examination of landscape plants, helps to determine when pest problems are reaching a critical damaging threshold. Scouting also helps to determine the stage (larva, pupa, adult) of the insects. If damage is noticed before an insect population is firmly established and when the insect is at a vulnerable stage, many problems can be easily thwarted by environmentally kind measures—ranging from hand-picking to hosing down with water to using soaps and oils. Flowering phenology and/or degree-day modeling also aid in determining pest activity and vulnerability. Flowering phenology studies the relationship of flowering to weather conditions and, by extension, to insect activity. Degree-day modeling is based on the number of days the actual average temperatures are above the minimum threshold for particular insect pest activity. Table 4 is a short list of some commercially available environmentally friendly controls.

Table 4. Environmentally Friendly Pest Controls
Control AgentTarget Pest
Green or common lacewings Aphids
Trichogramma wasps Moth and butterfly eggs
Lady beetles or ladybird beetles Aphids, scale, mealybugs
Predatory mites Mites
Nematodes Soil dwelling and boring insects
B. thuringiensis var. kurstakiCaterpillars, Gypsy moth
B. thuringiensis var. tenebrionis Colorado potato beetle
B. thuringiensis var. japonesis*Scarab larvae, including white grubs
B. popilliae*Japanese beetle larvae
Insecticidal soapSoft-bodied insects (aphids, scale, crawlers, mites)
NeemThrips, caterpillars
Horticultural oil Scale, aphids, mites, lacebugs

*Soon to be available
Adapted from Alternatives in Insect Management, MN Extension publication BU-5854.

Landscape managers and gardeners must make decisions on when to apply a pesticide by analyzing their expectations of "perfect" and recognizing the trade-offs involved in seeking the perfect landscape. Damage thresholds are related to both the level of damage a plant can tolerate, called injury threshold, and the amount of damage a manager can tolerate, called aesthetic tolerance. Such trade-offs include potentially harmful effects to soil and water quality, encouraging resistance of pests to pesticides, and possibly killing beneficial insects. By contrast, IPM seeks to maintain a natural balance.

When chemical pesticides are necessary, use the least-toxic one available and only spot spray. Carefully follow the label instructions and wear gloves, goggles, and long-sleeved clothing. Licensed pesticide applicators with access to pesticides not registered for use by the general public must follow additional precautions as indicated on the label. Premixed, ready-to-use products are convenient for urban gardeners and eliminate the problem of disposing of out-of-date, unused chemicals. If you mix your own, make sure to mix only what you need, use up all you mix, and triple rinse the container. For your safety and the safety of others, securely lock up all pesticides.

IPM Strategies at Work

A typical problem with paper birch (Betula papyrifera) trees—the bronze birch borer (Agrilus anxius)—illustrates how IPM theories and practices work. Birch trees naturally grow in cool forests. When these conditions are not met—when the tree is planted in alkaline soil in a sunny yard without a mulch to shade its roots and conserve moisture—it becomes stressed and subject to attack by the bronze birch borer. Symptoms of damage include dieback in the crown, a bumpy limb surface, and D-shaped exit holes. By routinely scouting urban plantings, you will notice such symptoms. If the problem is detected early (less than one-third of the tree is affected), the tree can likely be saved. Only after the dead branches are pruned out and the site is improved is any chemical control of the insect warranted. Good cultural practices come first in managing problems.

The insect (Adelges cooleyi) responsible for the Cooley spruce gall found on the branch tips of Colorado blue spruce and white spruce must also be managed through IPM. While these galls do not harm the tree’s health, large numbers can mar its appearance. Low numbers of galls may be removed. Spraying the galls has no effect on the insects since they are protected by the gall.

If chemical control is warranted due to heavy gall production over a number of years, the insect’s life cycle must be considered. The cycle starts in the spring when feeding by insect nymphs causes gall formation on the spruce. The nymphs mature by midsummer and fly from the gall to an alternative host, either the preferred Douglas fir or another spruce. More eggs are laid and the resulting insects feed on the Douglas fir, but do not cause galls. Later in the summer winged adults fly to the spruce to lay eggs, which produce the overwintering generation on spruce. In this complicated life cycle, sprays must be applied in early spring before protective galls are produced or in the fall when the adults prepare to overwinter. Cultural controls may be all that is necessary to control problems.

Alternative Strategies for Urban Environments

We can achieve a sustainable urban environment by carefully designing the landscape to reduce maintenance and by employing responsible management practices. Our landscapes should emulate the natural environment as much as possible. By engaging in PHC practices, such as encouraging biodiversity, composting our organic wastes, and using IPM principles to manage pests, we can improve the health of our environment and, at the same time, create a beautiful landscape.

PHC Management. PHC is a proactive approach. Design or redesign the landscape to minimize inputs of time, labor, fertilizers, herbicides, insecticides, and fungicides. Select the proper plant for the proper location and meet that plant’s cultural requirements. So often a gardener attributes the decline of a plant to disease or insect problems when the real problem is improper culture. Do not expect sun-loving bluegrass to grow in the shade; instead, landscape with shade-tolerant ground covers. Also, a plant suited to its site requires less maintenance. A healthy plant is better able to resist or recover from insect damage and disease infections. Whenever possible, use plant cultivars that are resistant to known insect and disease problems. Follow the IPM practices of inspecting and monitoring your plants’ health on a regular basis—before problems are out of control.

Biodiversity. Encourage a wide range of plants in the landscape. The naturally diverse landscape maintains a balance that discourages devastating outbreaks of disease or insect attack. Such a landscape also attracts birds and other wildlife, butterflies, and a variety of insects. Welcome insects into the garden, not only as food for wildlife, but because many beneficial insects prey on harmful ones, keeping them within bounds. Many insecticides kill beneficial insects as well as harmful ones.

Figure 3

Composting. Backyard composting is an ecologically sound way of disposing of yard wastes. Using compost as a soil amendment or mulch improves our urban soils, thus improving the health of our plants.

IPM. Trap or scout to determine the presence of pests. Only when insect numbers reach a damaging threshold should they be managed. Instead of routinely spraying for insects, spot-treat problems. Adopt IPM biological and biorational practices such as using soaps, oils, and Bt formulations that target the pest, not beneficial organisms. Use chemical controls as a last resort.

Following these principles promotes a rich and beautiful sustainable landscape, teeming with life, with little adverse effect on the environment.

We cannot expect perfection in our urban landscapes. If we can learn to accept and tolerate certain problems and prudently manage those we cannot, the return will be a healthy, sustainable environment that reaches well beyond our own backyards.


The following Minnesota Extension Service publications are available from your county Extension office or by credit card at 1-800-876-8636 (in the Twin Cities 612/624-4900). Prices and shipping charges subject to change:

Minimizing De-Icing Salt Injury to Trees, FO-1413
Protecting Trees and Shrubs Against Winter Damage, FO-1411
Recommended Trees for: Southeast Minnesota, an Ecosystems Approach, FO-6574
Recommended Trees for: Southwest Minnesota, an Ecosystems Approach, FO-6575
The Right Tree Brochure, FO-6506
The Right Tree Handbook, PC-5976
Ground Covers for Rough Sites, FS-1114
Ground Covers for the Midwest, BU-5777
Growing and Using Annuals and Bulbs, MI-6076
Ornamental Grasses for Cold Climates, BU-6411
Ornamental Grasses for Minnesota, FS-6422
Roses for the North, MR-6594
Disease-Resistant Vegetable Varieties, FO-2412
Alternatives in Insect Management: Biological and Biorational Approaches, BU-5854
Biological Control of Insects, FO-6345
Controlling Pests Around the Home, Non-Chemical Relief from Animal and Insect Pests, FO-3999
Environmentally Responsible Methods of Pest Control In and Around Homes, FO-6269
Lawn Care Practices to Reduce the Need for Fertilizers and Pesticides, FO-5890
Lawn Clipping Management, FO-3915
Responsible Fertilizer Practices for Lawns, FO-6551
Responsible Use of Lawn Care Pesticides, FO-5891
Turfgrass Management for Protecting Surface Water Quality, BU-5726
Watering Lawns and Other Turf, FS-2364
Backyard Composting, FS-3899
Composting and Mulching: A Guide to Managing Organic Yard Wastes, FO-3296
Options for Disposing of Leaves, FS-5570
Preventing Pollution Problems from Lawn and Garden, FS-2923
Structures for Backyard Composting, FS-5553
Guide for Rinsing Containers to Acceptable Standards, FS-6189
Rinsing Pesticide Containers, FS-3771
Understanding Pesticide Toxicity, FS-3947

Vera Krischik, associate professor
Kathyrn J. Bevacqua, sr. lab technician

Photo Credits:
David Hansen (Shade Gardening)
Beth Jarvis (Encourage Biodiversity)
Dept. of Entomology, U of M (Beneficial Insect: Adult




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