In this era where low maintenance and drought drive a number of design decisions, hardscape is one of the primary defining aspects in the landscape.  The project budget, the available materials, and the knowledge and quality of the installer are the only limits.  Hardscape includes walls to terrace slopes, provide privacy and define spaces; steps and walks or paths to direct traffic patterns; courtyards, patios, terraces, decks and plazas to serve both large and small gatherings; and fencing to provide protection, privacy and spatial definition.  All of these are part of the common landscape design palette.  Current trends for the higher budget plan might also call for outdoor fireplaces, grills and kitchens; fountains and pools; sport courts and playgrounds; sculptural elements; architectural screens; pillars and trellises or arbors.  Some clients want it all and can afford to pay for it while the average client is more budget conscious and will need to pick carefully among the design elements and the materials used to complete the job.  Hardscape elements form the structure of the landscape around which the plants, which tend to grow and change over time, become the ornamentation.  Thus anything that isn’t directly related to plant growth such as plants themselves, soil amendments, mulches and irrigation tends to be considered hardscape.

For the purposes of this article concentration is on the generally flat hardscape planes that tend to direct water and replace planted spaces.

In the interest of designing a water conserving, low maintenance landscape we often eliminate or redefine lawn and other planting areas and add new hardscape instead.  Adding solid hardscape (concrete, stone or brick on concrete and the like) eliminates watering, weeding, mowing, trimming, and mulching altogether.  A solid hardscape provides a smooth surface for ease of snow removal, placement of tables, chairs and other outdoor elements, for dancing, gathering, riding a tricycle or skate board and so on.  This solid hardscape space blocks air and water penetration.  Its impervious nature can cause runoff and potential drainage issues if not handled properly.  One is not allowed to significantly add to the historic drainage escaping the property line.  A landscape design that adds to the imperviousness of the landscape must consider the handling of the additional runoff created by this surface. Planning for the impact created by additional runoff can create opportunities.  Drainage can be directed toward lawn areas or planting beds where plants with higher water needs can be used.  One can direct downspouts into plant beds with the same aim.  A water feature, streambed or pool may be used as an area for runoff direction and collection.  Water quality may also be an issue when dealing with live plants and animals.  One needs to be careful not to use chemicals or other potentially toxic materials on or near the patio or walk where drainage is directed toward delicate plants and especially toward pools with fish.  If the area is large enough one could establish a wetland through which the water could be run before discharging into a water feature.  Wetlands are very effective at treating polluted water and can become an attractive amenity in the right landscape.  Solid hardscape should not be used around and under existing large trees as their roots will be unable to get the air and water they need.

Another type of hardscape which is commonly used and usually less expensive to install is stone, brick, precast concrete step stones and/or pavers laid dry in a carefully constructed bed of sand or sometimes over crusher fines or road base.  If the subsurface is well constructed, the joints are laid tightly and the surface is smooth this type of hardscape provides a solid surface for gatherings of people, outdoor furniture, tricycle riding and skate boarding.  It has the advantage of allowing water and air to penetrate its surface and can be successfully laid around existing trees (be careful of the roots though) and other plants.  The very properties that allow water and air to penetrate also have the potential for seeds of various plants to penetrate and grow sometimes creating an unsightly appearance and adding to the maintenance of the area.  Since this type of hardscape is not laid on top of concrete it also has the potential to heave and shift over time, making a surface that is difficult to sweep and shovel, more difficult to use for activities such as dancing, tricycle riding and skate boarding.  Directing water off this surface is not as important because most of the water will seep into the cracks between the pavers.  

Dry laid stone or larger precast concrete pieces can be installed with wide joints (2-4”) where mat-type ground covers can be grown.  Many people like this treatment as a less hard and formal look in the landscape.  Tables and chairs can still be used on this surface though it is not a satisfactory surface for trikes and skateboards.  One must be sure to keep the weeds out while the ground covers are establishing themselves and periodically thereafter. The upkeep is definitely higher and water may be needed for successful growth of the ground covers.  This surface is more permeable than the tight-jointed hardscapes described previously.  See the picture of a patio of this type established between two solid sets of landings and steps leading to this space.  The stone patio replaced an existing lawn.  The patio has a tightly laid cut stone edge with irregular stones and larger joints in the body of the space where thyme has been planted.  The replacement of lawn with dry-laid stone and low water-using ground covers saved water while providing an informal entertainment area for the clients. (see pictures, before and after)

One of the age-old maintenance and water use problems around the older parts of Denver is the parking strip or “tree lawn.”  This space between the street and the city sidewalk has been a tradition in Denver and, wisely or not continues to be required.  New projects within the City and County of Denver are required to have a tree lawn.   It is believed that the tree lawn creates a more street- friendly atmosphere and separation between the pedestrian space and the car.  Traditionally the city has allowed turf and high canopy deciduous trees in this space.  The city rule actually provides that nothing taller than 18” mature height can be placed on the ground plane of this “tree lawn.”  In many neighborhoods the tree lawn is so narrow that major problems have arisen where large trees have uprooted the sidewalks and grown over the curbs.  Irrigation of this area is difficult at best.  The result is often watering of the street and sidewalk and insufficient irrigation for the turf and trees.  One possible solution to this problem is to eliminate the lawn altogether, add hardscape in the larger places between the trees so that those who have parked along the street can easily get to the sidewalk, and plant low growing ground covers such as vinca minor or shade tolerant varieties of veronica around the trees.  Drip irrigation or netafim could then be used for irrigation.  The lawn would be gone but a feeling of green would be created with the ground covers while paving provides access to and from the sidewalk.  If the trees are very large and mature, the paving may have to be laid dry, on sand, allowing for air and water to get to the tree roots as well as accommodating the possible irregularity of the ground plane.  In wider tree lawns other possibilities exist.  In one instance we designed a curvilinear, dry-laid path system among four existing trees.  Several lower water-using evergreen ground covers were alternated in the spaces between the paths.  The paths were located so that pedestrians could progress from their cars to the main sidewalk and back again with ease.  The paving stones had to be cut and fit to accommodate the roots of the existing trees.  (See picture)  

As far as a sidewalk that has been ruined by the tree roots there may be several solutions to the problem.  One could replace the parts of the walk that are askew with a ramped length of walk creating a continuous flowing walk over the roots.  One could actually build a small bridge across the offending tree roots and ramp to the existing walk level on either side.  If the root area is relatively narrow a large stone or piece of pre-cast concrete could be used for the bridge surface, otherwise a metal or wooden platform might be needed.  The city generally frowns on anything that could be considered a “toe tripper” so care must be taken to create a seemless ramp and bridge combination across the offending roots.  One only wants to take these measures if the tree is worth saving in the first place.  If the tree is in poor health it might be better to start over with a smaller tree whose roots may not cause as much of a problem.

Gail Barry is co-owner of Land Mark Design Inc., a small landscape architecture consulting firm.  She is a registered landscape architect, a long time member of ASLA, an officer in CCASLA, and has practiced in Denver for over 28 years.