Excess lawn fertilizer and nutrients can be carried by runoff into storm drains.
For more information about lawn care and fertilizer issues:
Disposing of Unused Phosphorus (or other) Lawn Fertilizer:
- Use it in your compost bin or yard waste compost pile. The leaves need the nitrogen to break down and a little phosphorous won't hurt
- Use it carefully on your garden and shrubbery (not too much!)
- If the fertilizer contains pesticides and herbicides DO NOT use it in the compost pile but take these fertilizers to your nearest household hazardous waste collection site. (See the bottom of our lawn care page in the Home and Garden section of this website for help in finding a disposal facility.)
Here is more information on the 2005 MN statewide phosphorous-free lawn fertilizer law.
Lawn Fertilizer Doesn't Just Fertilize Lawns
Lawn fertilizer, especially when applied incorrectly, fertilizes
a lot more than just your lawn. Excess nutrients are carried
by runoff into streams and lakes. The same nutrients that
help grass grow also help algae and pond weeds grow, leading
to algal blooms and excessive aquatic plants that are not
only unpleasant to look at and to swim in, but also affect
food quality and habitat for fish and other organisms. They
also can lead to very slippery rocks.
Does this mean environmentally aware citizens are doomed to
have unattractive lawns? No. By following a few simple recommendations,
you can make sure that you're not contributing excess nutrients
to your streams and lakes.
Shoreland homeowners and businesses should
also consider the water quality and wildlife benefits of a more
natural setting for stream and lakefront property. Suggestions
may be found in the links below.
Responsible Fertilizing Practices
- Start with a soil test. Make sure your
lawn needs fertilizer, and find out how much you should
be applying. The Soil
Testing Laboratory of the University of Minnesota website
provides information on how to collect a soil sample and
where to mail it. Your test results will include recommendations
on what nutrients you should add to your lawn.
- Choose the correct product.
If you had a soil test, be careful to read the labels and
buy the correct fertilizer. If not, consider using phosphate-free
fertilizer (and therefore phosphorus-free). WHY?
Lakes and streams may be phosphorus limited. When excess
phosphorus from lawn fertilizer and other sources enters
streams and lakes, algae and other plants have all they
need (read more about the role of
phosphorus in your watershed below).
- Some cities, like Minneapolis MN, have enacted ordinances
limiting the use of phosphorus fertilizer in efforts to
protect water quality. More information about this ordinance and a
lawn fertilizer reduction experiment
can be found at Lake Access.
When you buy fertilizer the package will be labeled with three numbers.
The first number indicates total nitrogen (N), the
second indicates phosphorus (called available phosphate (P2O5) and the third, soluble potash (K2O).
Look for a middle number of zero, which indicates phosphorus free fertilizer.
- Apply the product correctly.
The following tips are taken from "Mugaas, R.J., 1995.
Responsible Fertilizer Practices for Lawns
University of Minnesota Extension, Publication #FO-06551-GO
- Fill granular fertilizer spreaders on a hard
surface where any spills can be easily cleaned up. NEVER
wash off fertilizer spills into the street or other hard-surface
areas where they can easily enter storm sewers and ultimately
surface water areas. Wash off granular fertilizer spreaders
over turfed areas to prevent runoff of fertilizer from hard
surfaces. Fill and clean liquid fertilizer applicators over
turfed areas for similar reasons.
- Close the gate on the fertilizer spreader
when crossing hard-surface areas or go back and sweep
up the material. Reuse it another time or put it back
into the spreader.
- Try to use a drop spreader, which is slower but more
precise than a rotary type spreader near surface
water. Next to shoreline areas, apply fertilizer around
the perimeter of the property with a drop spreader to
create a safety zone. The rest of the area farther away
from the shoreline can be fertilized with a rotary spreader.
Since the perimeter has already been done with the drop
spreader, it is not necessary to hug the shore because
fertilizer may get into the water. The same kinds of precautions
should be taken when using liquid fertilizer.
- Avoid getting fertilizer into natural drainage
areas or pathways on a property. These areas may not necessarily
be hard-surface areas, but they can carry fertilizer directly
into the surface water before having the chance to infiltrate
into the surrounding turf/soil area.
- Leave grass clippings on the lawn area to
decompose and recycle nutrients back to the turf area.
They should not be blown or raked into street gutters
or onto sidewalks and driveways where they may be carried
with runoff water to surface water. Nutrients released
in water through decomposition may cause undesirable algae
and vegetative growth.
- NEVER apply nitrogen fertilizers to water
resources directly or to frozen ground.
The Role of Phosphorus in Your Watershed
Phosphorus (P) is relatively sparse in natural soils and exists
primarily as the phosphate molecule that tends to stick to
soil as water moves through it. Therefore, in the absence
of human-caused impacts, P concentrations in the surface and
groundwater that flows into streams and lakes tends to be
very low and so usually regulates the potential amount of
algal growth in the system. In pristine parts of the world,
there is also very little phosphorus in precipitation and
in the dry portion of atmospheric inputs referred to as dry
Human activities lead to increased inputs of P in streams
and sometimes in groundwater and even in atmospheric inputs.
The most obvious sources are from municipal wastewater (sewage)
treatment plants and from industry and are called point sources
that are regulated by monitoring loads at the ends of their
discharge pipes and setting strict limits. Diffuse, or non
point sources, are much more difficult to measure and to control.
Agricultural fertilizer-P is a major source of phosphorus
pollution in streams throughout the US.
The major sources of P to most urban streams
and lakes are non point, are all controllable to a large extent
by homeowners and/or local community agencies and typically
- soil-P from erosion (construction sites, road
banks, shoreline disturbance, lawns & gardens)
- road runoff (street sweepings of crud that accumulates between
- roof runoff
- lawn clippings
- excess lawn fertilizer runoff
- sewage from leaky sewer lines or from improperly constructed
or maintained on-site septic drainfields
Lake internal inputs
Over long periods of time, urban lake sediments become greatly
enriched in phosphorus and then release a portion back into
the water. This internal release can occur sporadically and
may exceed annual inputs from surface waters.
In productive, moderately deep lakes that stratify
thermally in summer and become anoxic (no oxygen) in their
hypolimnetic bottom waters, large amounts of this historically
deposited phosphorus is released from the sediments into the
water. It can then be mixed into sunlit surface waters during
windstorms and fuel algal blooms. Turbulence from the wind
can also resuspend high-P sediment from shallow areas, as
can boat and jet ski wakes. This latter source is worsened
when the shoreline and nearshore zone submergent and emergent
vegetation (weeds) have been removed since they stabilize
the bottom sediment and act to dissipate wave energy.
How well do lawns filter runoff? Dig deep for the answer
Source: John Barten, Water Quality Mgr. Hennepin Parks. Written
for Focus 10,000-Minnesota's Lakeside Magazine
Nutrient Movement from the Lawn to the Stream?
Are lawns really a significant source of nutrients to urban
surface waters? Do enough nutrients find their way to urban
streams to cause water quality problems? You may think you
know the answers to these questions, but chances are the issue
is more complex than you thought. Explore this clearly written
article that tackles the current research and trends surrounding
Practice of Watershed Protection, Center for Watershed Protection (Article #4)
Where does the phosphorus in my watershed go?
Supplement what you've learned about nutrient movement in
your watershed with this short video presentation by the city
of Golden Valley.
Lakescaping for Wildlife & Water Quality,
by Carrol L. Henderson, Carolyn J. Dindorf, and Fred J. Rozumalski.
St. Paul, MN: Minnesota Department of Natural Resources, Section
of Wildlife, Nongame Wildlife Program c1998. Available for purchase at the