Ask an Expert: Steep Slopes Create Landscaping Challenges

Gardening season is upon us and you may have some questions. For answers, check out Ask an Expert, an online question-and-answer tool from Oregon State University’s Extension Service. OSU Extension Teachers and Master Gardeners respond to questions within two business days, usually less. To ask a question, simply go to OSU Extension Website, enter it and include the county where you live. Here are some questions asked by other gardeners. What is your?

Q: I need to remove creeping evergreens on a slope and replace them with suitable ground covers. They should be low maintenance and drought resistant. – County of Klamath

A: One of the challenges many homeowners face when laying out steep slopes is soil runoff. Topsoil on hills can wash away easily, leaving an unattractive, muddy mess. In this case, you might want to consider planting your hillside with ground cover plants. There are many varieties of shrubs and flowers that can thrive on slopes, giving you a better view and reducing the risk of erosion. Just keep in mind that you may need to bring in additional soil and an erosion mat to establish the plants if the existing soil on the hill lacks the necessary nutrients.

Another popular option is to terracing sections of the slope into your lawn to create flat planting areas. Building multiple levels on a hilly property will help you avoid erosion and allow you to add a variety of plants and landscaping elements for a functional and attractive design. Retaining walls can be made of a variety of materials to best suit your space and budget, such as stone pavers, wooden studs, or concrete. However, when considering materials that stand the test of time, stone pavers are recommended. Also, when installing a retaining wall, it is important to add a good drainage system behind the wall to prevent the wall from cracking or even collapsing.

Getting plants to settle on a hill can be tricky, as slopes tend to erode quickly due to drainage issues and soil runoff. If you don’t want to level your slope, adding rocks of various shapes and sizes is another way to hold the soil and allow your plants to establish themselves. Adding natural elements, such as a rock garden, can give your slope a natural landscape look that is both visually appealing and requires less maintenance.

Whichever method you choose to landscape your slope, it’s also important to select the right type of plants for the area you live in and your particular space. For example, deep-rooted plants can help stabilize the soil, ground covers are great for covering up unattractive spots, and ornamental grasses and perennials can be used to add color and texture to your slope.

When selecting your plants, it’s also important to keep maintenance in mind. Plants that don’t require shearing or a lot of annual cleaning can save you time in the long run. Here is some additional information. –Chris Rusch, OSU Expansion Master Gardener

Is this trimmer damaged?OSU Extension Service

Q: From the attached photo, can you tell me what, if anything, I should do about the wound on our dogwood trunk? Also, what do you think could have caused it? – Polk County

A: Trunk injury is typical of damage caused by a lawn mower, edger or other type of collision. The wound seems to be healing, as expected. Dressings are no longer considered recommended as they tend to trap bacteria in the wound. With exposure to air alone, the tree will repair the wound.

I suggest removing the mulch several inches from the trunk of the tree. Also, the irrigation line seems to be too close to the trunk. The trunk does not benefit from soil moisture. The most important place for irrigation is near the tree’s drip line or slightly beyond it. This is where root growth takes place. – Lynne Marie Sullivan, OSU Expansion Master Gardener

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KatsuraOSU Extension Service

Q: What’s wrong with my “Red Fox” katsura tree? The leaves look like they are getting enough water, but the leaves look funny on a few branches. We are in Zone 8, facing east at Junction City. The tree is on a deep root sprinkler system with two tubes and is watered for 22 minutes every six days. – Lane County

A: This is most likely the result of the sudden change from cold and damp to scorching heat. We are seeing a lot of leaves with weird and worse colors right now. – Pat Patterson, OSU Extension horticulturist, retired

Q: I have potted camellias and the soil pH is fairly neutral. I would like to lower the pH to 5ish. What is the best way to achieve this goal? – Yamhill County

A: You can change the pH slowly over time, allowing plant roots to adapt easily. OSU Extension has an excellent publication, “Acidifying Soil for Blueberries and Ornamental Plants” which is a detailed guide to doing just that – making the soil more acidic. After reading the post, look for fertilizers for acid-loving plants at your favorite nursery. – Anna Ashby, OSU Expansion Master Gardener

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spider and beeOSU Extension Service

Q: Could you put into words what’s going on with these three creatures – the spider, the bee and the one “waiting in the wings”? – Benton County

A: The spider is a goldenrod crab spider (misumena vatia). They hang out on flowers (including but not limited to goldenrod) and ambush insects. Looks like he got the bee (Apis mellifera) on your sunflower this way and it feeds on it. The other bug “waiting in the wings” is a bit more mysterious. It’s a type of true fly (order: Diptera), but I can’t see enough detail to know for sure what type of true fly it is. Interestingly, there are small flies like the one called zombie flies (Family: Phoridae, Boreal apocephalus) that parasitize and kill bumblebees and bees. Here is a link to a photo showing one of these flies on a bumblebee.

Adult zombie flies stalk adult bees and lay their eggs there. Then the fly larvae hatch and feed inside the bees, changing their behavior and eventually killing them. I don’t know if it’s a zombie fly trying to parasitize the bee that’s already being fed by the spider, but it’s a possibility. – William Gerth, OSU Expansion Master Gardener

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Wet spring leads to small heads of garlicOSU Extension Service

Q: I followed your OSU Extension brochure for growing garlic and the bulbs never got very big. I bought some good cloves and fertilized and watered a little in the fall. The tops rose, without a bulb on them, planted in October and harvested last week. – Clackamas County

A: I’ll let you decide which reason you may be able to correct for next year in the following Garlic Mistakes article. My best guesses would include planting too early. We generally recommend November for planting here in PNW. (I see the OSU brochure says September to November, but conventional wisdom says later is better).

My other guess would be our rainy, rainy, rainy spring. Maybe there was just too much water in the soil to allow for bigger bulbs. I don’t usually dig my garlic until July, so I’m not sure how mine fared this year, but another website says that small bulbs can be related to soggy soils and we definitely had it! Do not abandon. Plant what you harvested this year or get some new bulbs for next fall, because when you pull out a huge bulb with big cloves, there’s nothing better. – Rhonda Frick-Wright, OSU Expansion Master Gardener

Terri S. Tomasini