How to Build a Rain Garden in the Landscape

This rain garden was constructed on a previously flat property in Water Mill, Long Island NY.

Our project goal was to transform a wide open landscape into an intimate space with detailed retaining rock gardens and a diverse sustainable deer resistant planting.

The first consideration was the root system of a mature oak tree. The excavation zone and the retaining rock garden shape was determined by the root system profile. Retaining was  necessary at the sides of the rain garden but we were able to slope the grade leading into and out of the garden.

The next consideration was the rain garden liner and shape. A heavy duty liner was chosen to be able to withstand the wetland and walkway construction. The liner was extended all the way up to the retaining rock to provide moisture to the lower rock garden plantings as well as providing humidity to the moss areas.

On this project we developed a zig zag walkway to provide access directly through the rain garden. This design provided an easy walking surface with interest that enables a visitor to go right down into the garden. The wood walkway is constructed on top of the rubber liner with padding and cement footings.

Before the garden is back filled we sloped all the property drainage into the rain garden as well as the roof water. Overflow level was established with overflow weep holes feeding several plant pockets and the remaining overflow water is plumbed into the existing roof water dry wells.

Wetland plants require different planting soil. The bulk of the rain garden is back filled with sand 6″ to 12″ below the underside of the walkway (depending on the plants water requirements) with the individual planting pockets amended for each plant. The wetland plants were chosen for flowering time, height, shape with some evergreen perennials for winter interest.

The rock gardens were planted with drought resistant alpines and the remaining landscape was planted with deer resistant plants such as Cephalotaxus, Pinus mugo, Leucothoe, Picea, Cornus, and Magnolia.

The garden paths and walkways were covered with medium fine gravel to provide a comfortable walking surface and to prevent erosion into the rain garden.

Visit the rock garden canyon that Emil Kreye & Son inc. installed at Long House Reserve in East Hampton NY. LONGHOUSE SITE

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How to Build a Stream in Your Garden

To build a stream, site evaluation is necessary. The surrounding topography must relate to the water feature. How would water flow through the property naturally, or, what do we need to change to make a stream look as though it flows through the property naturally.

Grade changes are a perfect opportunity to create new interest features in the landscape. A slope on a property is an asset that should be used properly and not wasted. Digging out a slope to build a waterfall will provide for a larger cascade but additional retaining will be necessary. Sloping the waterfall building area will enable the stream to meander with little cascades and a minimal amount of pooling.

On many waterfall projects retaining is necessary. How we decide to retain an area makes a big difference. Retaining walls divide up space. Often it is preferable to build a retaining wall that looks natural. This style of wall does not chop up the property but becomes part of the landscape. The introductions of plants add interest and intimacy.

Instead of using a conventional retaining wall on a project we can use natural rock ledges harvested and re-installed. This method of retaining enhances the project with many living spaces and plant pockets. The rock ledge appears to have been there before the house.

On flat properties a stream may look the most natural. Each level of a cascade can provide different interests and different planting environments. By building usable places in the garden we can lure a visitor into a unique space. This living wall is always evolving; each visit evokes a different experience.

The most important principle to keep in mind is that streams and waterfalls should fit into the landscape.

STREAM CONSTRUCTION – STEP BY STEP:

  1. Excavate area to the elevation of the pool beam or the edge of the pond.
  2. Stabilize the building area. This is the most important part of the project. Depending on how heavy the rock installation, tamped soil, soil cement or a cement foundation may be necessary.
  3. Slope toward the pond, this will prevent the water from running back under the waterproofing material.
  4. Install waterproofing rubber. We do not recommend using cement because it cracks over time and leaks.
  5. Arrange rocks on the rubber carefully. A poorly placed rock can result in a hole in the rubber, which will cause leaking problems over time.
  6. Arrange the retaining rocks outside the rubber to retain the grade.
  7. Install plantings.
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