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Urban Site Challenges
March 12, 2017
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Preferred Characteristics of Urban Plants
March 12, 2017

Structure and Disease Resistance

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Structure and Disease Resistance

Featured Image: Ulmus spp., Elm

Urban Approved plants must have good structure, require low-to-minimal maintenance, and have no major insect and disease issues. These characteristics mean different things for different plant categories, which are explained below.

Trees

Urban Approved trees must have strong branching that resists wind damage and will not pose a hazard to pedestrian and vehicle traffic, or structures. Urban approved plants should not be prone to disease that causes branch death of large limbs, creating overhead hazards. This is not to say that branch dieback is bad; many trees, like Honeylocust and Birch, will occasionally get diseases that kill smaller twigs on the tips of branches. These small branches, however, do not pose a threat to human safety and property.

It is important to remember that regardless of species or cultivar, all trees require a regular pruning cycle to maintain good structure. While Urban Approved trees have better form than other species, they are not exempt from this fact. Trees typically require pruning every 5 to 10 years, depending on species and growth rate.

Shrubs

Urban Approved shrubs must also be disease resistant, especially to those that damage the ornamental value of the plant. Flower buds must be hardy to our climates and flowering should be reliable with little maintenance. If the plant is known for its outstanding leaves, then it must be resistant to foliar disease. Required maintenance on shrubs must be low-to-minimal, not requiring more than basic mulching and pruning to maintain form. They should not be a plant that becomes unmanageable and overgrown if not annually maintained.

Evergreens

Urban Approved evergreens are meant to be viewed year round, so they must have durable foliage that is not easily killed. All evergreens experience some form of seasonal needle drop each year; this is a normal part of the growing process and cannot be avoided. Similarly, some evergreens change color in winter as they move resources from their needles back into the plant. This discoloration may be considered unsightly by some, but it is a natural part of how evergreens survive. What we are more concerned with is permanent needle death in evergreens, which disqualifies them from the Urban Approved designation. For this reason, Urban Approved evergreens must be resistant to salt spray, winter burn, and foliar diseases.

Perennials

Urban Approved perennials must be relatively easy to establish, flower reliably (when applicable), and require little care in the landscape to keep healthy. Maintenance should consist of cleaning up the dead foliage once or twice per year, watering in heavy droughts, and applying an annual mulch cover. Plants that require special care when it comes to fertilization, pest control, or annual staking and shaping are not eligible for Urban Approved status.