Anderson, James

Gustafson, David M.

Jaster, Marguerite

Meyer, Mary H.

Olson, Kenneth M.

Pedersen, Brad

University of Minnesota Digital Conservancy

Landscaping Septic Systems 
COLLEGE OF AGRICULTURAL, FOOD AND ENVIRONMENTAL SCIENCES 
Man; H. Meyer, Extension Horticulturist 
Brad Pedersen, Extension Horticulturist 
Marguerite Jaster, Landscape Desig11 Assistant 
Department of Horticultural Science 
James Anderson, Extension Soil Scientist, Department of Soil, 
Water, and Climate 
Kenneth M. Olson, Extensio11 Educa tor, Sherburne County 
David M. Gustafson, Extension Specialist, Onsite Sewage 
Treatment, Biosystems and Agricultural Engineering 
Landscaping near and around septic systems is 
of concern to many homeowners. Whether 
drainfields or mounds, Minnesota septic systems 
must have a minimum of three feet of unsa turated 
soil between the drainfield or point of infiltration and 
limiting soil condition such as hardpan, bedrock or 
saturated soil in order to properly treat sewage. A 
mound system is required if three feet of separation 
cannot be achieved with an inground trench system. 
Mound systems are designed to maximize the 
absorption capaci ty of existing soil (see Figure 1). 
Mound loca tion, size, shape, construction procedures 
and maintenance of the mound all interact in deter-
mining how well the system will function. Placement 
of plants on and near the mound must be done with 
care to ensure a properly functioning septic system. 
Plants enhance the system by removing moisture and 
nutrients from the soil and providing cover to 
prevent erosion. 
Mound Placement 
A rectangular mound rising 18 inches to 5 feet 
above the surface of a relatively flat home landscape 
may be quite noticeable and possibly very unsightly. 
Careful design planning before the mound system is 
installed can help to create a sustainable landscape 
with lower maintenance costs, grea ter environmental 
benefits, and much higher aesthetic value. Mounds 
can be placed to suit individual landscaping and lot 
size needs (see Figures 2 and 3). Properly landscaped 
areas around the mound can serve as privacy barri-
ers, windbreaks for homes and a screen from un-
sightly views. 
As a homeowner considering the placement of a 
septic mound, know your options. The earlier in the 
process that you become involved in expressing your 
preferences, the more options you will have. For instance, 
before the house is designed or built, potential septic 
locations, along with soil borings and percolation 
tests, can give some control over the placement and 
final outcome. County or city ordinances set dis-
tances from wells or lakes, based on the appropriate 
This publication is meant to be used in conjunction 
with the Septic System Owners Guide, PC-6583 
which further explains the site requirements for 
placement and location of a mound system. See 
back page for ordering information. 
Septic tank 
Mound/ 
3-foot separa tion l 
to saturated soil 
Saturated soil 
Illustration by James Kiehne 
Figure 1. Cross section of a mound system. 
state standards and rules (typically 100 feet) or 10 
feet from property lines (PL) or rights-of-way (see 
Figure 4). Additionally, on even a slight slope, it is 
paramount that the mound rockbed be on the con-
tour for proper operation of the system. Soil must not 
be moved to create a different slope, as this reduces 
the ability of the soil to accept the effluent. Once the 
drainfield or mound is determined, protect it from 
compaction and disturbance to ensure proper sewage 
treatment. 
When planning a landscape, there should be an 
invisible or concept line the eye follows around the 
yard (see Figures 2, 3 and 4). Where space allows, this 
line is a graceful curve which represents the division 
between two different types of plant material (turf or 
ground cover versus shrubs) or between plants and 
hard goods (turf, patio or deck). The concept line 
becomes a real bedline where the lawn ends and the 
shrubs begin. If your property is large enough to plan 
UNIVERS ITY OF MINNESOTA 
Extension 
W I 1• 
Figure 2. A and B represent possible placement of mound 
septic systems. 
an unbroken turf area as the first priority, then place 
the septic system beyond the bedline disguising it as 
part of a shrub or perennial area or screening it with 
trees or large shrubs. If your property is smaller, 
blending the mound into the overall landscape is still 
the key. Try moving the focal point from the mound 
to other plants or features. Extending the actual 
berm with additional topsoil at the same height and 
curving the perimeter, then sloping down and away 
can conceal the existence of the system (see Figure 4). 
If the drainfield must be located near a drive, patio, 
or walkway, retaining walls may be used to save 
space, but only on the uphill side of the berm. 
Connect the extended berm to another large fea ture 
in the yard, such as a pool enclosure or other fenced 
area, using retaining walls for transition. ALWAYS 
design with the entire yard or viewing area in 
mind-connect it to the whole picture. 
Guidelines for Planting on and Near 
Septic Mounds 
It is very important that the integrity of the 
mound be kept intact and that soil does not wash 
away. A permanent vegetation cover is required to 
minimize topsoil loss. Open sites are more suscep-
tible to frost, heaving and erosion. Plants trap snow 
which acts as a mulch and prevents erosion. 
• Topsoil on the mound should be a minimum of 6 
inches and a maximum of 30 inches. 
• Use minimal tilling when planting and establish a 
cover as soon as possible to limit erosion. 
• Always wear gloves when working over septic 
systems to minimize your contact with soil. 
• Use plants that do not like water or wet soils near 
the septic system. This will prevent their root 
systems from interfering with the septic system. 
The larger the plant, the more extensive (not 
necessarily deeper) the root system. 
Figure 3. C and D show additional mound system locations. 
• Do not place trees and shrubs ON the mound; 
they may be planted at the foot or on side slopes. 
Frame the mound with trees and shrubs at a 
distance, but use only herbaceous (non-woody) 
plants on the mound itself. Trees should be 
planted a minimum of 20 feet from the edge of the 
mound. Trees known for seeking water reservoirs, 
such as poplar, maple, willow and elm, should be 
planted at least 50 feet from the mound. Shrubs 
should not be planted on top of the mound. 
• Avoid irrigation and fertilization on a mound; in 
fact, never plan to irrigate this area. Use plants 
that can withstand dry conditions. Plants listed on 
the back page tolerate and thrive on natural 
rainfall in Minnesota. 
• Minimize traffic on the mound, both human and 
animal, to avoid soil compaction. Do not exercise 
pets or stake pets on septic mounds. Never drive a 
car or other vehicle across the mound or mow 
when the soil is wet. Compacted soil can lead to 
soil erosion and impedes the flow of air around the 
system. In winter, activity on a mound can cause 
frost to penetrate resulting in freezing problems. 
• Do not plant edible plants, such as vegetables and 
herbs on a mound or drainfield. 
• Annually inspect the mound for animal damage 
such as burrowing and tunneling. Control animals 
at the first sign of tunneling or burrowing before 
damage is extensive. 
• Root barriers (geotextiles impregnated with a long-
lasting herbicide that kills plant roots) have been 
used around mounds. Installation is expensive 
and can be avoided with proper plant selection. 
f ~ B~4ZO b 8 l /lo l .Zf FT 
t Housf 
.sEPTIC SYSTEM 
Jf 
KEY: ::It = FILL OR ADDITIO 
A_;Jtl,;,;. = ~~1g~~~~s~~s 
Figure 4. Model landscape plan for mound septic system. 
0 = TREES A D SHRUBS 
=LAWN 
PL= PROPERTY LI E 
Suggested Plants for Use on Septic Mounds 
Herbaceous plants, such as wildflowers and 
grasses, are good choices for mound plantings. 
Grasses are especially desirable due to their fibrous 
root systems which hold soil in place. Grasses also 
provide year-round cover. 
The following native prairie plants grow well 
on dry soils and would be good choices for a mound 
septic system: 
Wildflowers 
prairie onion (A/lium stellatum) 
pussytoes (Antennaria neglecta) 
butterflyweed (Asclepias tuberosa) 
heath aster (Aster ericodes) 
bigleaf aster (Aster macrophyllus)* 
Pennsylvania sedge ( Carex pensylvanica)* 
prairie clover (Oalea spp.) 
pale purple coneflower (Echinacea angustifolia) 
rattlesnake master (Eryngium yuccifolium) 
wild geranium (Geranium maculatum)* 
prairie smoke ( Geum triflorum) 
oxeye (Helianthus helianthoides) 
rough blazing star (Liatris aspera) 
wild bergamot (Monarda fistulosa) 
penstemon (Penstemon spp.) 
pasqueflower (Pulsatilla patens) 
violets (Viola spp.)* 
Grasses 
sideoats grama (Bouteloua curtipendula) 
blue grama (Bouteloua gracilis) 
little bluestem (Schizachyrium scoparium) 
prairie dropseed (Sporobolus heterolepis) 
June grass (Koeleria macrantha) 
* shade tolerant 
These plants are propagated by seed or plants. 
A combination of both will make a faster cover. Use a 
mulch of clean straw or a cover crop of annual 
ryegrass or oats to prevent erosion while the plants 
become established. 
Low maintenance lawn grasses, such as fine 
fescues, can make a dense cover and only need to be 
mowed once or twice a year. Mow in October and 
late June to reduce weeds. Fescues are traditional 
lawn grasses that tolerate dry soils and shady sites. A 
mixture of fine-textured fescues, such as creeping 
red, hard and sheep's fescues (Festuca rubrum, 
Festuca longifolia, Festuca ovina), in equal proportions 
can be seeded at the rate of 3.5 pounds per 1000 
square feet. Traditional lawn grasses, such as com-
mon Kentucky bluegrass and perennial ryegrass, can 
be planted on a mound and regularly mowed. 
Mowing will increase evaporation from the mound 
and aid in rodent control. 
Perennial flowers, such as daylilies and 
peonies, can be grown; however, extra care must be 
taken to mulch or plant close together so soil will not 
be exposed and erode. Low maintenance plants that 
do not need tending and care (remember minimal 
Figure 5. Pasqueflower is a native wildflower that tolerates 
dry soil conditions. 
traffic on the mound) are best. Enjoy from afar, and 
do not walk on the mound. 
Proper selection and placement of plants best 
suited to the site means that those plants will be 
healthier, more attractive, and have fewer pest 
problems. 
References and Further Information 
Septic System Owners Guide, PC-6583 
Plants in Prairie Communities, FO-3238. 
The publications can be ordered from the 
University of Minnesota Extension Service. Call 
(612)624-4900 or 1-800-976-8636. 
For landscape design publications, refer to 
SULIS URL in Extension site: 
www.sustland.umn.edu 
FO-6986-B 
1998 www.extension.umn.edu 
Additional copies of this item can be ordered from the 
University of Minnesota Extension Service Distribution 
Center, 20 Coffey Hall, 1420 Eckles Avenue, St. Paul , MN 
55108-6069, e-mail: order@extension.umn.edu or credit 
card orders at 800-876-8636 or 624-4900 (local calls) . 
Printed on recycled paper with minimum 10% postconsumer waste. 
Produced by Communication and Educational Technology 
Services, University of Minnesota Extension Service. 
In accordance with the Americans with Disabilities Act, this material 
is available in alternative formats upon request. Please contact 
your Minnesota county extension office or, outside of Minnesota, 
contact the Distribution Center at (612) 625-8173. 
Copyright© 1998, Regents of the University of Minnesota. All 
rights reserved . Send copyright permission inquiries to: Copyright 
Coordinator, University of Minnesota Extension Service, 405 
Coffey Hall , St. Paul, MN 55108-6068. E-Mail to 
copyright@extension .umn.edu or fax to : 612/625-2207. 
The University of Minnesota Ex1ension Service is an equal 
opportunity educator and employer. 


Landscaping Septic Systems

http://conservancy.umn.edu/bitstream/11299/219501/1/Ext_Septic.pdf

Landscaping Septic Systems

Abstract

Similar works

Full text

Available Versions

University of Minnesota Digital Conservancy