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Friday - April 17, 2015

From: Wyndmoor, PA
Region: Mid-Atlantic
Topic: Soils, Shade Tolerant, Grasses or Grass-like, Herbs/Forbs, Shrubs, Wildflowers
Title: Plants for a Shaded Slope in Philadelphia
Answered by: Anne Van Nest


I have a small slope along the North side of my house in a suburb of Philadelphia. A small maple tree grows there but most of it gets no sun at all (a large segment is under the tree). I had the soil tested at Penn State and it is very acidic. Last summer I added nitrogen/phosphate just like it was recommended from Penn State but I think the rain probably just washed it all away. It was very very dense soil. So my questions are 1) how to I prepare such dense soil for planting and 2) what specific grasses/sedges/small shrubs/herbaceous plants do you recommend?


Let’s start first putting together a list of native plants for your area. Take a look at the Native Plant Database on the website and put in the following search criteria: State = Pennsylvania, habit = herb (for herbaceous), duration = perennial, light requirement = shade, soil moisture = dry.  Then select the height you desire. This will generate a list of herbaceous plants. Do the search again for grasses and grass-like plants and shrubs to add to your list. 

The nitrogen that you added last summer is water soluble and has probably leached away. Penn State Extension has information online about the 12 soil regions of the State. Philadelphia is in the Coastal Plain soil region.

Coastal Plain

The soils of the Coastal Plains section developed in coastal sands. These soils usually have a sandy surface texture and are well drained. Because the topography is level, erosion potential is typically low. The soils contain few rock fragments but have moderate root zone available water content due to the coarse soil texture. This region has the longest and warmest growing season of Pennsylvania. Most of the area is occupied by the city of Philadelphia and its suburbs.

Melissa Miles, Philadelphia Sustainable Agriculture Examiner has published an article in about determining your soil type. She says that most soils in Philadelphia are characterized by a heavy clay content and describes a simple test to determine this and how to use the soil triangle.

And to amend your clay soils, The NC Cooperative Extension Service has an Urban Horticulture factsheet on Amending Clay  Soils with many good tips such as “Adding organic soil amendments to the soil lightens soil texture, discourages compaction, adds nutrients, improves drainage and aeration, moderates soil temperature, and provides pore space, which is essential to plant growth. Clay without organic matter is like a flattened deck of playing cards. Adding organic material jumbles the cards, permitting water and oxygen to enter the soil.”


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Plants for soil with basalt outcroppings in Idaho
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