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Permeable Landscape Choices

Published:
July 26, 2016
By:
David Jacknin
Permeable Landscape Choices
Stepping stones across gravel form an elegant, easy-to-maintain
If you are thinking about how to surface the patio, terrace at your new home, consider alternatives to hard paving, such as decomposed granite, pea gravel, volcanic rocks, rubber mulch and even oyster shells, which are relatively soft underfoot and won’t disintegrate with use. Permeable materials allow water through their surfaces and work especially well for pathways. From a design perspective “soft materials” make a nice contrast with plants and hardscape, and allow you to create pathways in any shape desired.  They are also softer on the feet and help 

make a smooth transition from house to garden, as shown here in Plan 888-2 by architect Nicholas Lee, where decomposed granite, commonly known as DG, creates an uncluttered surface.

Decomposed granite is made from granite that is ¼ inch in size or smaller. It is a feature of Mediterranean garden design. Decomposed granite can be used for patios and pathways and though relatively impermeable, it is very attractive and the least expensive choice. It's available with a stabilizer mixed in or you can add it yourself. The stabilizer reduces runoff and helps create a stable and beautiful surface. Pea gravel, available in a wide variety of sizes and colors, is very permeable and provides excellent drainage. Because pea gravel is a rounded river rock, it shifts easily and should be used in low traffic areas. Rubber mulch is especially useful in playground applications; a layer of 6 to 9 inches is recommended.

Gravel interspersed with flagstones or other stepping stones is a way to add texture while creating a path 

through a larger outdoor space, as shown here in Mediterranean style Plan 484-8 and Plan 496-1 at the top of this post.

We asked landscape designer Nick Thayer of Late Afternoon Garden Design for his advice on "soft paving" patio materials. He says to “design what you need" while keeping the following points in mind:

-- Take cues from the adjacent architecture and existing color palette.
-- Know your budget.
-- Ask how walkable the material you like is, and is it easy to maintain.

Which material requires less maintenance?
Decomposed granite is the lowest maintenance and lowest cost but least permeable.

Are there other types of rocks that you recommend?
Quarry fines (byproducts of the crushing and washing operations at rock quarries) are used on the East Coast and are good for pathways because the fines stay compacted in place and are comfortable to walk on. [Nick has also used recycled glass and ceramic chips, as shown in this sustainability project in San Francisco, photo courtesy Nick Thayer.]

What are the advantages of permeable materials?
We all live in a watershed. These materials help ground water recharge.

Is it necessary to have a gravel layer below the decomposed granite or pea gravel?
Because soil expands and contracts it is very important to have good base separation. Base rock is ideally 4 to 5 inches thick with a layer of landscape cloth below.

Do you recommend using a stabilizer with decomposed granite?
Yes, it reduces tracking into the house and extends the lifetime of the pathway.  I also recommend a hardscape surface such as a concrete stoop located between the pathway and the house to reduce tracking.  I use PolyPavement  - a good quality stabilizer.

Is there any particular source of pea gravel you recommend?
Make use of locally sourced pea gravel. The color palette usually works well because it is local to your area and the carbon footprint is minimized because the material is nearby.

How about play areas? What do you recommend here?
Pea gravel is good. It should be in a layer at least 3 inches thick. Another choice is engineered play bark.  This is available everywhere and is the least expensive alternative.  A third alternative is recycled rubber matt. This is made from recycled tires and comes in 2’ X 2’ panels or 1’ X 1’ panels that are 1 ½ to 2 inches thick. For matt or crumb rubber don’t use base rock but compact the soil first. 

How about other materials?
Black lava rocks works well with  mid -century  modern architecture.  It replicates the original style. We’ve used oyster shells for bocce ball courts.   

What is your favorite material for pathways?
I like crushed rock, ¼” or smaller. It is very stable. Make sure to have some hardscape between the crushed rock and the house so sharp rocks won’t track onto hardwood floors.

For a collection of plans with courtyards and patios suitable for "soft surfacing" click here.