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Healthy hedges can be biological corridors

“If we connect tiny isolated natural areas by building biological corridors between them, the species that live there can intermingle and increase their populations.”

— Douglas Tallamy, “Nature’s Best Hope,” 2019

Last week, I discussed Douglas Tallamy’s recommendation to add more native plantings in our landscape in order to support local wildlife and ecosystems. Tallamy argues that native plants are more effective than non-natives in providing food and shelter for local birds and insects.

My red-tip photinia hedge, a hybrid of species that originated in Asia, is a good example of the lack of interaction between a non-native plant and native wildlife. The photinia’s sprays of pretty white flowers attract lots of European honeybees but no native insects, and their red berries don’t supply the nutritional needs of native birds.

Why should I care whether my photinia hedge supports native wildlife? I planted the evergreen shrubs to provide a privacy screen, but if my goal is to increase biodiversity in my yard, I need to add plants that contribute to the food webs and successful reproduction of native animal species. Otherwise, my landscape supports only a few generalist insects and the birds that feed off them.

Increasing biodiversity goes beyond altruistic notions of saving wildlife. Raising the number of native plants and animals enhances the “carrying capacity” of our gardens and landscapes.

We take these services for granted: clean, oxygen-rich air, clean, accessible water, flood control, weather moderation, fertile topsoil, pollination, carbon sequestration, natural pest control, and many others. But without biodiversity, local ecosystems become destabilized, ecological services are degraded, and the quality of life for all of Earth’s inhabitants breaks down.

Tallamy makes a good point when he says conservation efforts are strengthened when people become more familiar with local wildlife. Last week, I provided the website for the National Wildlife Federation’s Native Plant Finder (www.nwf.org/NativePlantFinder/), which provides pictures and descriptions of local native plants and the butterflies and moths they support.

The Audubon Society also has a native plants database that links native plants with local birds they support (www.audubon.org/native-plants/). For example, blueblossom (Ceanothus thyrsiflorus), an evergreen shrub with clusters of pretty blue, purple or white flowers, can attract 18 different species of birds, including native species of chickadees, wrens, waxwings, nuthatches, woodpeckers and warblers, as well as 93 species of native bees and butterflies.

Adding native shrubs to our hedgerows is one of the best ways to increase interactional diversity in our landscapes, in which different plants and animals work as a community. If people worked together in the same way, our hedges could become much more than ornamental privacy screens; they could become what Tallamy calls “biological corridors” that connect our landscapes to each other and to larger wilderness areas nearby.

In my neighborhood, the hedges are predominantly English laurel and photinia shrubs, both non-natives that I have in my front yard. Over the past few years, my photinias have become infected with blackspot, a fungal disease that commonly affects photinias, roses and berry bushes. The fungus is spread from plant to plant by airborne spores, and it overwinters on leaves and in leaf litter. My photinias are particularly susceptible to disease because as the tree canopy has spread in my yard, parts of the hedge no longer get enough sunlight for optimal health. I’ve noticed several photinia hedges in the neighborhood are infected with blackspot.

During late winter dormancy (February/early March) is a good time to prune off diseased foliage on evergreen shrubs, thin out branches to increase air circulation, and apply a natural fungicide to treat the blackspot (avoid applying in freezing temperatures). However, it’s also a good time to rethink my hedgerow design and plantings. I’ve learned that one of the most effective ways to prevent an outbreak of disease or insect infestation is to use different species of plants in my hedge.

I’ve decided to gradually replace the photinia with native evergreen plantings, including blueblossom, tall Oregon grape (Mahonia aquifolium), Oregon boxwood (Paxistima myrsinites), and evergreen huckleberry (Vaccinium ovatum). By using different types of plants, I’ll be able to position the hedge shrubs according to their sunlight requirements. Rather than a straight, flat-topped hedgerow, I’ll create a more natural-looking border for my yard.

Here are tips for planting or transplanting shrubs: Make sure the location and growing conditions in your landscape are right for the plants you want to grow. Space the plants to accommodate their mature size. Soak the plant roots thoroughly before planting and gently loosen the roots so they are free from the rootball. Be sure to handle the plant by the rootball, rather than the trunk or stems.

Dig a hole twice as wide as the rootball and deep enough so the flared base of the trunk is just above ground level. Loosen the soil in the planting hole and rough up the sides of the hole with a shovel so the roots can grow freely. Don’t add soil amendments to the hole; they tend to keep roots from fanning out from the plant.

After making sure the plant is straight, backfill the hole with the soil that was removed, water again thoroughly and apply a thick layer of mulch around the plant, avoiding the trunk. Even if the shrubs are drought tolerant once established, the young plants will need adequate moisture to establish a healthy root system. On the other hand, more newly planted trees and shrubs die of overwatering than lack of water, so use a moisture probe to check the soil past the top few inches and adjust irrigation accordingly.

Our hedges serve us well: they add privacy, block wind and beautify our landscapes. If we grow the right plants, our hedges can provide benefits well beyond the borders of our yard.

Rhonda Nowak is a Rogue Valley gardener, teacher and writer. Email her at Rnowak39@gmail.com. For more about gardening, check out her podcasts at https://mailtribune.com/podcasts/the-literary-gardener and her blogs at www.literarygardener.com.

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My garden to-do list this week

Prune shrubs, fruit trees and grapevines

Transplant rose bushes

Begin sowing vegetable seeds for transplanting: peas, bulb onions, leeks, leafy greens, broccoli, cabbage, radishes, beets

Begin sowing cool-season annual flower seeds for transplanting