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Tuesday, June 4, 2013

Harvesting Rain: Permeable Paths, Patios and Driveways

Brick walkway in Mother Nature's Backyard.  Laid in decomposed granite,
this path is permeable to water

Walkways, driveways and patios are the second largest impermeable feature(s) in many yards – second only to the roof.  We’ve discussed capturing roof runoff over the past three months (February-April 2013).  This month we consider ways to turn other impermeable features into rain-harvesting surfaces. 

Many Southern California homes have walkways, driveways and open patios of poured concrete.  This traditional style has definite advantages: the surface is smooth, hard, durable and relatively inexpensive.  The main drawback (from a water conservation standpoint) is that water runs off concrete rather than infiltrating into the ground.  In addition, older concrete surfaces often develop cracks and chips, making them less attractive and functional.  As water becomes scarce, many of us are rethinking our larger expanses of concrete and asphalt.

There are more options today than ever before, whether you’re planning a new patio or replacing an old walkway.  New materials and methods – and some older methods that are being ‘rediscovered’ - allow us to create permeable surfaces that retain the benefits of older, impermeable surfaces.  The use of permeable surfaces is gaining popularity world-wide, so you’re in good company if you’re reconsidering your impermeable surfaces.

Next month (June 2013) we’ll discuss the topic of garden water use more generally. We’ll even provide a ‘Water Wishes’ questionnaire to help you to define water goals for your garden.    You might want to read that posting before you continue.

Summer is a great time for garden planning.  With many garden chores at a low point, summer provides time to research your options and even install new hardscape if appropriate.  Below we present a brief overview of permeable hardscape.  Much good information on permeable surfaces exists on the internet, providing further discussion, advice and details on installation.  We’ve suggested some of our favorite sites below, but there are many other excellent internet and print resources.

Must I consider permeable options?  
If you like your current impermeable surfaces, consider capturing the runoff in a rain garden or vegetated swale.   Study the drainage patterns; if the walk/patio was properly installed, the water may already drain into your garden.   If water currently ends up in the storm drain, evaluate the feasibility of capturing it using a simple swale or rain garden (see March and April 2013 posts).   Alternatively, you might want to simply cut down on the area.   A smaller patio or driveway – or one that combines both permeable and impermeable areas – may be just the ticket.
Another reason to retain impermeable surfaces is if your soil drains very slowly.  You can easily determine your soil drainage (see March 2013 posting).  Most local soils have adequate drainage; but if your soil drains less than an inch an hour it may not be appropriate for permeable hardscape.  You may want to work with a landscape professional to improve the overall drainage and infiltration in your garden.

Permeable Walkways, Patios and Seating Areas
Walkways, patios and seating areas can be major living areas in our climate.  We’re outdoors most months of the year and patios/seating areas make this possible.   Major walkways and paths – like the walkway to the front door – get heavy foot traffic, while other walkways likely get occasional use.  The first step in re-thinking your impermeable surfaces is to consider their use:

  • How often are they used/how much foot travel per week?   Could they be used more if improved?
  • Are they conveniently located (or are people always using ‘alternate’ paths) ?
  • Are they too small/narrow?  Too large?
  • What is good about them?  What could be improved?
Time spent in thoughtful planning and observation usually pays off handsomely when designing a garden.  Rethinking your garden allows you to seriously consider just how well your garden enhances and supports your lifestyle.   Perhaps you don’t currently have enough space for activities like outdoor dining.   Or perhaps your entry walk is inconvenient – or just plain ugly.   Now may be the time for change.
Hardscape features like seating areas and walkways play an important role in defining how a garden looks.   But they also facilitate the use of garden spaces.    Look critically at your current hardscape – the good and the bad.  What works well?  What is frustrating?   Re-thinking your hardscape allows you to enhance what is good, change what needs improvement and even add new features to make your garden more enjoyable and useable.
Several practical considerations are important when re-thinking your impermeable surfaces.  The most important of these are:

  • Appropriate location: ease of use
  • Safety
  • Appropriate material/design for level of use
  • Local building regulations and ordinances/covenants
  • Cost /ease of installation and maintenance
  • Aesthetic considerations:  style/material should complement and enhance the house and garden
  • Extra points: materials that are locally produced and/or recycled

Locating your pathways/walkways and seating areas for easy use is extremely important.  The most logical location is often the one that appears to be natural: the informal ‘path’ that everyone takes when crossing the front yard;  or the place where lawn chairs end up on summer days.  When planning a seating area consider how it will be used.  If access to electricity, water, the kitchen or shade are important, plan accordingly.   Remember, rethinking your hardscape allows you to re-design it, making walkways and seating areas more convenient.


When considering a permanent patio, major walkway – or anything in the front yard – review your local building codes, ordinances and/or covenants to be sure that your plans conform to regulations.   This is important whether you have a contractor do the actual work or you plan to do it yourself.   The codes/regulations are there for a reason – often related to safety.   Better to design according to code than have to remove a structure built ‘not to code’.

Perhaps the most important planning determinant is the amount and type of use your walkway or seating area will need to support.  All aspects of design – from width and slope of walkways to the materials/installation methods used – impact the suitability and safety of a hardscape surface.  Major pathways and heavily-used seating areas should provide a firm footing and be easily traversed by all – including those with physical handicaps.    Occasional-use paths (such as those providing access for garden maintenance) can be less robust.  The emphasis is on appropriateness and safety for the amount and type of use.

The main walkway to your house must provide safe, easy access.  Check your local regulations – nearly all municipalities have codes that cover specifications for major access paths and driveways.   The same is true for paths/walkways in parking strips and verges. 

A surface that supports high level usage need not be covered with concrete or asphalt.   There are many good permeable options for high, medium and low use areas; the range of materials continues to expand with increasing demand.   The options vary widely in their cost of installation and maintenance; be sure to consider routine maintenance and longevity when choosing a material.  Some materials and designs are best installed by an experienced professional while others can be easily done by the home owner.   That may also figure into an appropriate choice.

Arizona Sandstone and Brick Walkways: Mother Nature's Backyard

Permeable hardscape materials range from brick and stone to organic mulches.  Some materials (brick, stone; some types of gravel, crushed rock and pavers) are appropriate for more formal garden designs while others (bark mulch or decomposed granite) are more informal in appearance.   All other things being equal, choose a material that complements the garden/house in color and design; hardscape features (walkways and seating areas) have a strong visual impact.   

We’ve listed the most common materials used in Southern California gardens – grouped by use level - at the end of this article.  The list covers the costs, limitations and best uses for the different materials.  We hope you find this useful.  You don’t necessarily need to use new; recycled bricks, pavers, concrete chunks and other materials can sometimes be obtained at low cost from Craig’s List and other recycling resources.
Arizona Sandstone in high-use areas of
Mother Nature's Backyard

In Mother Nature’s Backyard we’ve installed several types of walkways.  The more formal – and highly trafficked - central areas of the garden demonstrate the use of brick (lead photo), Arizona Sandstone (rock; photo above)  and ‘urbanite’ (recycled concrete; photo below).  These materials differ in looks and cost, but all provide a firm surface that infiltrates water well.   All contribute to the semi-formal ‘look’ of our central garden area.

'Urbanite' (Recycled Concrete) Walkway set in decomposed granite
Professional mason lays Sandstone Pathway on a base of decomposed granite

Our brick, stone and urbanite walkways were laid on a bed of decomposed granite rather than being mortared in on a concrete base (see above).   This method – sometimes called dry-laid construction – requires an under-layer (base) of construction sand, gravel and/or decomposed granite which provides a firm base that will infiltrate water.  The sand or decomposed granite is also filled between the bricks/stones to hold them firmly in place, making a study and attractive surface.  To learn more about installing this type of permeable walkway or seating area see:

Decomposed Granite Pathway: Mother Nature's Backyard

The lesser trafficked (and more informal) north part of the Mother Nature’s Backyard garden features a path of decomposed granite (photo above) that  also provides a firm, permeable walking surface.   The informal look of decomposed granite complements the ‘natural’ look of this part of the garden.   In areas that are even less frequently accessed (for example, around the rain garden) our garden features ‘stepping stones’  (photo below) and paths of chipped wood mulch.    These surfaces are not as easy to traverse, but still provide useable access during most of the year. 

Stepping Stones of Arizona Sandstone:
Use of single material adds visual continuity

In choosing the hardscape for Mother Nature’s Backyard, our primary consideration was appropriateness for the level of use and safety.  As a public garden, many areas of the garden must be readily accessible – much like a front yard walkway.  For these areas, we chose materials primarily from the high/mixed use list, below.   

A secondary (but important) factor was aesthetics.   Among the appropriate choices, we carefully considered materials that looked nice but were also affordable.  Garden visitors are surprised to learn that our bricks were donated – for the price of hauling them away.   The bricks add a striking visual note to the garden entry and complement the greenery of the foliage; and the price was right.   Another surprise is the appearance of our ‘urbanite’ walkway.  This path has the semi-formal look of native stone at about ¼ the price!  Like us, you might want to use more expensive materials in ‘high visual impact’ areas and lower cost materials elsewhere.    

It’s sometimes difficult to visualize how a hardscape project will look once completed.  Pictures on the internet can be extremely useful and are readily available for many materials.   Visit local gardens and take pictures of ideas you like.  Home landscaping books from the library can provide a wonderful source of information.  If you live locally, we urge you to visit our garden for some hardscape inspiration.   We’ll be happy to answer your questions about pathways and seating areas.

Permeable Driveways

More people are installing permeable driveways than ever before.  There are several options available, most of which require professional installation. The following resources will get you started on the topic of permeable driveways.

Suggested Materials for Permeable Hardscape (walkways; paths; seating areas)
Suggested Materials for High and Multiple Use Areas – These areas include driveways, parking areas, high-use walkways and patios.  All materials provide a firm permeable surface. 
Best Uses
Installation: Moderate/ high
Maintenance:  low/ moderate
Limitations: cost; more complex jobs best done by professional masons
Infiltration:  Low to high, depending on spacing
Best Uses: Tight brick can be used for all residential needs; loose (dry set) brick is good for areas less frequently used.
Decking (wood or wood substitute)
Installation: High
Maintenance: High
Limitations: Expense; usually needs replacing every 15-20 years. Wood substitutes (Trex, etc) are often plastics.
Infiltration:  Moderate to high, depending on gaps between planks
Best Uses: While expensive, decks can provide a beautiful surface for outdoor seating, dining, etc.  Can be combined with other materials.
Installation: Moderate
Maintenance: Low
Infiltration:  Low to high, depending on gaps and degree of slope.
Best Uses: Seating areas & walkways. Easily installed/ repaired; lots of different ‘looks’ -  wide variety of shapes, sizes, and colors.
Porous Asphalt
Installation: High – must be professionally installed
Maintenance: Low. Need to clean out pores with water occasionally. 
Limitations: ?Shorter life than regular asphalt.
Infiltration:  Low to moderate.
Best Uses: Good replacement for current asphalt driveways. Petroleum based and produces tainted run-off.
Porous Concrete
Installation: High – must be professionally installed.
Maintenance: Low. Need to clean out pores with water occasionally.  Limitations: ?Shorter life than regular concrete.
Infiltration:  Low to moderate.
Best Uses: Can be used instead of conventional concrete anywhere around a home.
Stone – Natural, Recycled, or Manufactured 
Installation: Low to high depending on the type of stone and base material.
Maintenance: Low/moderate  depending on plants and/or materials used to fill the gaps.
Limitations: Cost
Infiltration:  Moderate to high, depending on size and spacing.
Best Uses: Seating areas, walkways.  Usually laid on a sand/gravel base; can sometimes be sunken into the soil instead, if soil is well-drained and plants are planted between  stones.
Recycled Concrete (‘Urbanite’)
Installation: Low to moderate depending on source of ‘urbanite’ and base material
Maintenance: Low/moderate  depending on plants and/or materials used to fill the gaps.
Limitations: not quite as attractive as stone – but not bad!
Infiltration:  Moderate to high, depending on size and spacing.
Best Uses: low-cost alternative to stone – can be used in any situation where sandstone or other stone might be used.    If you are replacing old concrete,  recycle the old concrete chunks in your own yard.
Paving Grids / Permeable Paver  Grids / Porous Pavers/ Gravel Cells
Installation: Moderate
Maintenance: Moderate to high (if the grass has to be mowed and regularly irrigated).
Infiltration:  Moderate to high.
Best Uses:  Paving grids can be filled with gravel or crushed rock to form a firm driveway or pathway.  For lower-use areas they can be planted with study grasses.  Grids are plastic, cement or cinder-block.
Suggested Materials for Medium Use Areas (like the part of the driveway that is driven on, but not parked on and the sides of houses; paths that get frequent use) allow a greater flexibility in the materials used. Appropriate materials include all those listed under ‘High and Multiple Use’ as well as those listed below.  Consider using locally-produced and/or recycled materials where ever possible.
Best Uses
Crushed Aggregate (Crushed Rock; ‘Crusher Fines’)    Crushed concrete
Installation: Low
Maintenance:  Low. 
Limitations: May be tough on bare feet/children and some consider it unattractive. Weeds can become a problem.
Infiltration:  High
Best Uses: Makes a compacted walk or patio area - used extensively in Europe. Many grades (particle sizes) & colors. 
Pea Gravel; Small Pebbles
Installation: Low cost for Pea Gravel; moderate cost for pebbles
Maintenance: Low. 
Limitations: Does not compact into solid surface. Weeds can become a problem.
Infiltration:  High
Best Uses: Softer on feet.  Probably best for children’s areas, utility areas, vegetable garden paths.
Decomposed Granite (DG) including stabilized DG       
Installation: Low cost;  more expensive than pea gravel,  mulches.
Maintenance: Low.  Add more DG as needed (every 3-5 years).
Limitations: particles stick to the bottom of shoes.
Infiltration:  Moderate to high.
Best Uses: Casual/natural appearance. Excellent for garden paths, casual seating areas,  side yards.
Installation: Moderate (higher than DG; usually professionally installed);
Maintenance:  low
Limitations: must order large quantity – best for large area; edges can erode
Infiltration:  Little; water runs off the waxy surface
Best Uses: Good for trails, paths in public areas or with moderate use.
Turf Block (grass pavers) - concrete blocks with holes  filled with soil and planted. 
Installation: Moderate
Maintenance: Moderate to high (if the grass has to be mowed and regularly irrigated).
Limitations:  Maintenance
Infiltration:  Moderate to high.
Best Uses:  Drive-over/non-parking areas of driveway; utility areas that get moderate traffic. 

Suggested Materials for Low Use Areas (such as garden access paths) allow for the most flexibility in choices.   Any of the materials used in high- and medium-use areas can be used in low-use areas.   In addition, common mulches make natural, environmentally appropriate choices for these uses. 
Best Uses
Chipped Bark
Installation: Low
Maintenance: Low
Limitations: Needs to be renewed yearly; less easy to walk on than high- and medium-use choices
Infiltration:  High
Best Uses: Casual/natural appearance. Fine grade bark makes a  good  walking surface (medium to large grades can be difficult to walk on – better used as mulch).
Shredded Bark (‘Gorilla Hair’)
Installation: Moderate
Maintenance: Low/moderate
Limitations: Moderately expensive for mulches; needs to be renewed yearly
Infiltration:  High.
Best Uses:  Casual/natural appearance.  A better walking surface than most mulches.  Best in moist and non-windy areas.
Tree Chippings
Installation: Free/low
Maintenance: Low
Limitations: Needs to be renewed yearly; less easy to walk on than high- and medium-use choices
Infiltration: High. 
Best Uses: Casual/natural appearance.  Best for low-use areas like access paths for garden maintenance.   Can be used as a mulch/mulch path.
Rock; Pebbles; Lava Rock
Installation: More expensive than organic mulches
Maintenance: Low
Limitations: Cost; color choice; hard to walk on if used alone
Infiltration:  Moderate to high, depending on spaces between rocks and surface below.
Best Uses: River rock is not a good walking surface – better as mulch in windy, exposed areas.  Can be used as decorative filler around pavers, for walkway edges.
Recycled brick chips, glass chip mulch
Installation: May be expensive
Maintenance: Low
Limitations: Cost; color choice; hard to walk on if used alone
Infiltration:  High.
Best Uses: Excellent as accents in smaller areas, for example around pavers; many colors, sizes
Additional Resources on Permeable Paving


Feel free to add a comment below.   You can also e-mail your permeable hardscape questions to: mothernaturesbackyard10@gmail.com 





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