Low Impact Development Manual for Michigan - OSEH - University ...

Description and Function
Planter boxes receive runoff from multiple impervious
surfaces, including rooftops, sidewalks, and parking
lots. Runoff is used for irrigation purposes, and the
vegetation in the planter box absorbs stormwater and
releases it back into the atmosphere through evapotranspiration.
Boxes can take any form and can be made out
of a variety of materials, although many are constructed
from wood.
Construction specifications are critical to ensure that
an appropriate volume of runoff from smaller storms
“feeds” the carefully selected vegetation types in the
boxes; however, consistent watering is necessary during
dry periods.
In general, planter boxes must be carefully designed to
accommodate the desired amount of runoff. In addition,
plantings must be carefully selected, and boxes must be
carefully maintained, to accomplish stormwater objectives,
and perhaps, most importantly, to succeed in a
landowner’s overall landscaping objectives.
Stormwater benefits of planter boxes include reduction
in runoff volumes and some reduction in peak
rates of runoff. Boxes which overflow also effectively
reduce peak rates of runoff. Depending on the type of
box selected, evapotranspiration will increase along
with infiltration and groundwater recharge. Water quality
may benefit, depending upon how much runoff is
directed into the ground and prevented from worsening
erosive stream flows.
When well designed, installed, and maintained, planter
boxes are extremely attractive additions to homes,
commercial businesses, and office buildings. In fact,
an essential objective in developing planter boxes is to
enhance overall landscape aesthetics. Boxes are ideal
for buffers around structures, foundation plantings,
providing seat walls, and for defining walkways, patios,
terraces, drives, and courtyards.
Variations
Of all the BMPs listed in this manual, planter boxes are
probably the most adaptable to all types of sites with
all types of site constraints. The infiltration variation is
influenced by all factors which are limiting to any infiltration-oriented
BMP (i.e., bedrock/seasonal high water
table at or close to the surface, very poorly draining
soils, etc., all of which are described in the Infiltration
BMP of this manual). However, both the contained and
flow through variations can be used on virtually every
type of site ⎯ large or small, front yard or backyard,
flat or sloping, shady or sunny.
Contained
Contained planter boxes (Figure 7.42) are generally
traditional planters that have weep holes to drain excess
water from the planter. They effectively reduce impervious
area by retaining rainwater which slows stormwater
runoff from draining into sewers. Contained planters are
used for planting trees, shrubs, perennials, and annuals.
The planter is either prefabricated or permanently
constructed in a variety of shapes and sizes. Planters are
typically placed on impervious surfaces like sidewalks,
plazas, and rooftops. Contained planters may drain onto
impervious surfaces through their base or into an overflow
structure.
Figure 7.42
Schematic of Contained Planter Box
Growing
Medium
Top of soil set 2”
From top of
planter filter
fabric
Weep Holes
for drainage
Impervious
Surface
Source: City of Portland, OR Bureau of Environmental Services
LID Manual for Michigan – Chapter 7 Page 259
12’-18’