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www.urban-forestry.com 35 Woody and Herbaceous Plants for Slopes in the Southeastern U.S. This woody plant list was prepared by Arborguard Tree Specialists Vice President & Chief Operating Officer Jamie Blackburn; they are plants that work well for him on slopes in the southeastern United States. Check to make sure they are appropriately heat-tolerant or cold-hardy for your region before considering them. If you would like Blackburn's recommended herbaceous plants for slopes list, send a request to citytreeseditor@gmail.com. As anyone who has ever tried to garden on a slope knows, it can be an arduous challenge. Gravity and drought are almost always working against you, making erosion control and plant estab- lishment difficult. Maintenance becomes more of a headache, as even keeping your balance while working can be tricky. Based on several years of woody groundcover research I con- ducted at Cornell University with Nina Bassuk (see resulting bulletin here), as well as over 20 years of field experience in the nursery, landscaping, and arboricultural industries, I offer here some advice for successfully designing, planting, establishing, and maintaining interesting and functional slopes. As is true for any type of landscaping project, site assessment is critical. Knowing sun/shade patterns, aspect (which direc- tion the slope is facing), soil drainage, soil type, presence of underground infrastructure (especially in urban areas), pres- ence of existing vegetation, and any microclimate effects will help determine any site modifications that may need to be performed and will help guide plant selection. It is rarely recommended to till or amend a slope, as that can increase erosion potential. If soil organic matter is an issue, a simple top-dressing prior to planting of 1 to 2 inches (2.5 to 5 cm) of compost can help. It may also be necessary to divert the water coming from above the slope using swales or drains so that excessive erosion can be avoided after soil disturbance and planting. Jute blankets pinned down to the soil can also be helpful. At planting time, just cut appropriate holes in the jute to allow for planting. Over time, as plants establish, the jute will biodegrade. It is imperative that you start weed-free, and depending on whether you have annual, biennial, and/or perennial weeds, getting the site completely weed-free prior to planting can often take more than one growing season, depending on the time of year you start the project. Both pre-emergent and post-emer- gent herbicides can be extremely helpful in this regard, but use them carefully and according to label recommendations. Plant selection is the next important decision to be made. One important thing to know about any type of ground covering plant is the method by which it spreads. Is it rhizomatous or stolonif- erous? Can it be overly aggressive or potentially invasive? Will it spread by self-seeding? Will it tip-layer itself as its arching stems come back in contact with the ground? If it is to be a mixed planting, do the plants behave in the same manner with a similar growth rate so that one will not outcompete the other? Spacing and installation size is also a factor to consider. Research has shown that installing a smaller size plant from the nursery (i.e. a rooted cutting or a quart or 1-gallon container plant) at closer spacing can achieve cover and therefore weed suppression faster, as opposed to installing larger sizes (i.e. 3-gallon or balled-and-burlapped plants) at farther spacing. On purely utilitarian sites, hydroseeding can also be an option. A list of recommended woody plants that I find work well for slopes in the Southeast US region is included in this article for reference; some of these plants may work for you if they have the appropriate cold or heat hardiness for your region. I also prepared a list of recommended herbaceous plants for slopes which you can request from CT Editor Michelle Sutton at citytreeseditor@gmail.com. Once the site has been assessed and prepared and plants have been selected, planting can begin. It is recommended that all plants be placed out on the slope prior to digging so that spacing and placement can be adjusted as needed. Oftentimes, what made sense on paper in the design process does not make sense on the actual site, so stay flexible! It is sometimes easier to spread a 2 to 4 inch (5 to 10 cm) layer of wood mulch prior to planting, place the plants, and then dig. If you do so, be careful to pull the mulch back from each plant as you dig so that the roots are in contact with the soil and the holes do not backfill with mulch, which will cause the plants to dry out too quickly. This is especially true if using rooted cut- tings or small container plants. Try to smooth out the soil and mulch on the slope as you plant. After planting, make sure to carefully "fluff" the mulch around the crowns of the plants so that the stems are not buried under excessive mulch, which can cause the plants to rot before they become established. As for any kind of new planting, careful watering is critical to establishment. If watering by hand, be sure to use a wand and breaker so that erosion can be avoided. If using a sprinkler or automatic irrigation, be sure that coverage is adequate without causing runoff and that the site is not over-watered. It is imper- ative to keep the newly planted slope well-weeded, likely by hand, during the first two growing seasons. This can be a huge factor in the success of the planting, so be sure to consider it when planning for labor and budgets and schedule. Herbicide use can be very risky after planting, if not impossible. Once plants become established, annual pruning to remove dead, diseased, or broken branches is recommended. For her- baceous plants, cutting back the stems in fall can be beneficial and will give the slope a tidier look for winter and spring. Top- dress with a 1 inch (2.5 cm) layer of compost annually, and refresh mulch as needed, being careful to never let the compost and mulch depth together exceed 4 inches (10 cm), and from piling up against stems of woody plants. Over time, plants may need a hard rejuvenation pruning, especially larger shrubs. —Jamie Blackburn, Vice President & Chief Operating Officer, Arborguard Tree Specialists, Avondale Estates, Georgia