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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Tuesday - April 28, 2009

From: Rogue River, OR
Region: Northwest
Topic: Planting, Shrubs, Trees
Title: Shallow topsoil on rocky substrate in SW Oregon
Answered by: Jackie OKeefe

QUESTION:

I want to plants some shrubs and trees. Trouble is I can't plant very deep. I have mostly rock within 5 inches. Please help.

ANSWER:

Thank you for sending your question to us at the Lady Bird Johnson Wildflower Center. Since our mission is to inform about and promote the use of our native plants, we will point you to some resources and ideas that help you find native, well-adapted plants for your soils, topography and climate.

Okay, so you don't have a lot of topsoil. There are native species which have adapted to thrive on stony, thin-clad ground. And there are other considerations. Some are physical parameters – light, slope, moisture, exposure, wind. Others are choices – height, form, plant features like flowers, berries or thorns. Are you trying to create a screen? Do you want winter foliage or light penetration? What kinds of wildlife might find cover or forage in your landscape? Since shrubs and trees are long-term additions to the landscape, think about the long-term size and characteristics of your choices and remember the acorn thing (mighty oak trees...some things get really big).

A partial "fix" for your soil depth issue, especially if you are on a slope, is to raise and level the ground by creating small terraces. The raised end of the terrace allows you to increase soil depth, and prevents unchecked erosion. As the shrubs and trees grow more extensive root systems, they become part of the stabilizing mechanism. (When adding a new soil horizon, it is important to cultivate and mix the existing soil with the added layer so the plants roots transition into the lower soil layer.)

To search for appropriate plants, go to our Native Plants Database, select Oregon, and run a couple of searches on shrubs and trees, narrowing to your light and moisture requirements. The search results will give you a list of possible plant choices, and the individual plant descriptions should help further narrow your list. Additionally, by clicking the USDA plant symbol just below the plant name and taxonomic description, you will be taken to the USDA database, where, by clicking on Oregon on the Distribution map, you will reach a county-level map of the plant's known distribution. There are also local organizations in your area that can give you good advice on selecting specific species for your particular site. Here are some web links:

Some native plant nurseries for Oregon

Some native plant activities in your area w/The Nature Conservancy

Native Plant List of local wholesale grower Althouse Nursery

 

Running a search on trees and shrubs for Oregon, here are a few possible choices:

Ceanothus velutinus (snowbrush ceanothus)

Quercus garryana (Oregon white oak)

Prunus virginiana (chokecherry)

Spiraea splendens var. splendens (rose meadowsweet)

Vaccinium ovatum (California huckleberry)

Juniperus communis var. saxatilis (common juniper)

 

 

 


Ceanothus velutinus

 

 


Prunus virginiana

 


Spiraea splendens var. splendens

 


 

 

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