By: John Weeks, Ettingers Landscaping, Montoursville PA

With its beginnings in the 1980’s the rain garden concept is an environmental initiative where water in the form of rain or snow that falls on your property is captured to reduce flooding and pollution problems. This water is then utilized to create a sustainable landscape and thus providing multiple benefits. Numerous ecological benefits may occur from creating a mixed naturalistic landscape that functionally reduces run-off water and any pollutants or contaminants that it may be carrying. At the same time naturalized plantings reduce the need for the intensive maintenance practices.

Flowering perennials, ornamental grasses and shrubs (native as a first choice) are utilized to create and environment attractive to birds, butterflies, and other wildlife that expands the biodiversity of your garden. Creating a mosaic of grasslands, wetlands, woodlands, shrubby areas and ponds will maximize wildlife value.

Humans seem to have instinctive attraction and fascination with water. How to gather, transport store and release rain water in a environmentally sustainable design provides new opportunities for the landscape designer.

The water cycle begins as water evaporates from the oceans, condenses into clouds which are transported by air currents and then deposited in the form of rain, hail or snow. It then makes its way back to the ocean, evaporates into the atmosphere or infiltrates into the ground. Roofs, roads, sidewalks, parking lots, patios, etc. are all examples of sealed surfaces that do not allow water to infiltrate into the ground where it falls. This prevents the natural process of filtration and purification and also reduces the potential to replenish ground water and our underground aquifers. At the same time the high rates of run off may lead to erosion, flooding and the carrying of containments into our streams, rivers and lakes.

The purpose of the water-sensitive landscape is to reduce or eliminate the amount of excess run off leaving the property or site and in so doing, pollutants held within the water are also contained within that landscape. Commercial and municipal sites are utilizing permeable paving and green roofs on any increasing frequency to facilitate water retention.

Green roofs and simply roofs that have a layer of vegetation added to them. They reduce the amount of water run off and the rate of run off. They provide winter insulation, summer cooling and sound insulation. A typical green roof consists of a waterproof base layer, insulation layer, root repellent layer, a drainage layer, a geotextile filter mat, the growing media and finally the vegetation. Structurally the building must be able to support the additional weight of the green roof and be absolutely waterproof.

GREEN ROOF INFORMATION

 
CHRRA Center for health Research & Rural Advocacy
Geisinger Health System, Danville, PA.

1. Is the roof in an exposed or sheltered location?
2. How will the plant be affected by wind, sun, heat, cold, desication?
3. Plant Selection
1. Herbaceous perennial offer color, texture, and variability, however they require a minimum of 4”of growth media increasing weight. The media must maintain a high level of nutrients and moisture thus promoting weeds. Most are not evergreen and have limited longevity.
2. Harden Succulents

The primary plants used for roof gardens. They survived drought and wind the best. Sedum, Sempervivum, Talinum and Jovibarba are the best choices. Sedums have the best survivability. There are over 600 species of sedum and are diverse in their visual interest. They are long lived and self-propagating or rerooting. They grow in 4”or less of substrate. By selecting proper varieties, you can have flowering from March through October.

1. Grasses

May add a vertical dimension, motion and different texture to the roof garden, however, they require a deeper medium (more weight), increased maintenance and may present a fire hazard. Some options include Andropogon, Bouteloua, Carex, Sesleria and Sporobolus.

1. Thymus, Origanum, Salvia and Allium all can work on garden roofs.
2. Bulbs

Dwarf varieties of iris, allium, tulips, daffodils, grape hyacinth and crocus should work.

1. Can the building’s construction handle the additional 15 to 24 pounds/sq. ft. of a green roof?
2. Is the growing medium lightweight, porous, free draining and can it still retain water well?
3. Can the medium absorb and supply nutrients, anchor plants, have enough weight to avoid floating when wet or be blown off when dry? Will it retain its volume?
4. Although seeds and cuttings could be used, plugs, vegetated meats or modules are often be used. The kind and amount of media in the container is not good for a green roof situation and may add sufficient weight to exceed the roof’s design.
5. Most roof garden installations take 12 to 18 months to establish when planted with two plugs per square foot.
6. Weeds can be a major problem during establishment and need control.
7. Pre-emergent herbicides may be used to control weed seeds with established plants.
8. The growing media should have sufficient nutrients for the first growing season. A year after planting, a slow release 14-14-14- fertilizer should be applied. After five years, fertilization may not be necessary.
9. A single thorough watering should be done following planting. The media should not dry out for the first three weeks necessary.
10. Spring planting (following the last frost) is the best time for the establishment. Only the initial watering should be necessary.

CHRRA Center for health Research & Rural Advocacy
Geisinger Health System, Danville, PA.