Water and Succession in Mind

Water and Succession in Mind

Site Conditions and Client Desires

The project is new residential construction in St. Paul.  The lot was vacant prior to construction.  Water runoff and management was and is a concern since the existing lot had slopes up to 40 percent in the front and up to 10 percent in the back.  The location also has mature oak and walnut surrounding the property, so tree survival after the building construction and the landscape installation was important.  

The clients desired a low maintenance and accessible design.  They desired a recessed patio off the sunroom in the back of the house for growing kitchen herbs and vegetables.  They had specific plant requests for the yard as well as minimal turf area. 

Water Management Design

The water management design focused on contouring the slopes to capture water from the hard surfaces of home as well as surface water flow through the landscape.  The surface water flows through a series of key-line swales specifically designed to slow water movement and retain water on site.  The swales are installed to change the slope from 10 or 40 percent to 1 percent.  The swale system allows for longer water absorption time and ground water storage, thus increasing groundwater recharge as well as increased water availability for plants.  The key-line swales lead to water infiltration areas (rain gardens) in the back and front yard.  The swale and water infiltration zones are designed to accommodate a minimum 4-inch rain event in the front yard and greater than 4-inch event in the backyard before any water exits the property.

Ecologically Based Planting Design

The plantings are ecologically designed to mimic nature and its different biomes.  The swale and water infiltration areas create different moisture zones throughout the landscape.  Plant species were selected for tolerance of lower moisture zones (dry) and other plant species were selected for tolerance of higher moisture zones (mesic and sometimes wet).  Plants were either directly planted or broadcast seeded with a winter wheat cover crop.   The back yard is primarily seeded and planted with prairie and savanna species, whereas the front and sides yards are seeded and planted with understory and woodland species.  The thermal-mass of structures and landscape features are also used to support marginal plant species such as Japanese maple and flowering magnolia.  Species succession is expected.  The herbaceous perennial plants (grasses and flowers) will migrate as tree shade changes.  The trees and shrubs were selected for the ability to thrive as the landscape matures.  The plant species were also selected based on fruit, flower, and seed production for homeowner use as well as wildlife attraction.

The existing perimeter oak and walnut trees were root pruned once per season two years prior to site excavation.  Root pruning was completed in the excavation zones to reduce stress on the trees once construction began.

Other Design Considerations

A recessed patio was installed in the back yard off of the sunroom.  The terraces will be planted with tender and perennial herbs, spices, and vegetables.  The terraces also allow for additional seating and staging locations.  The recessed patio has a disguised drain system that connects to the rain garden.  

An engineered retaining wall and step system was designed and installed in the front yard.  Care was taken to maximize tread depth and width to accommodate entry railings aimed at accessibility.

The plantings are designed to be ‘self-sufficient’.   Once established the only area that may require additional water will be the turf zone in the back yard and the kitchen garden in the recessed patio.  The landscape is designed to accommodate all plant waste from the plants, so there should be no biomass removal from the landscape.