Groundwater Protection - Water Wise Lawn Fertilizing
In some parts of the City, we see nitrate levels in groundwater on the rise. Nitrates in groundwater come from two main sources, septic tanks and lawn fertilizer.
Why is Nitrate a Concern?
Nitrate in drinking water is a health concern for infants - it disrupts the blood's ability to take up oxygen. Nitrates can also degrade surface waters like streams, and increase plant growth that depletes oxygen in Budd Inlet.
Fertilize with Care
If you want to fertilize your lawn, it's important to pick the right time and use the right amount of an organic or slow-release fertilizer for long-lasting results that also protect our water resources. Follow the tips below, and download our printer-friendly fact sheet on fertilizing your lawn for groundwater protection.
Pick the Right Time
For a spring application, wait until mid-May or early June when heavy rains have passed so that less fertilizer will leach away. Later fertilizing also helps avoid a growth surge when the lawn is already growing vigoriously-you won't have to mow as often. In the fall, September or early October is also a good time, before the heavy rain starts.
Pick the Right Product
When fertilizer nutrients are in slow release forms, they are available to plants over a longer period of time and less nutrients are wasted or lost as pollutants. Look for products that are:
- Organic; or
- Made from sulfur and/or polymer-coated fertilizer, isobutylidene diruea (IBDU), Methylene Urea, and Ureaform; and
- Have at least 50% Water-insoluble Nitrogen.
Choose the Best N-P-K Ratio
You'll see numbers like 8-3-1 or 32-3-3 somewhere on the back of the bag. The first number tells you what percentage of Nitrogen (N) is in the product. Look for a product that has a balance close to the 3-1-2 ratio.
Use the Right Amount
Follow these three steps:
Step 1: Measure your lawn. Pace off the approximate width and length of your lawn in feet and multiply those two numbers. This calculation will give the square footage of your lawn.
Step 2: Read the bag. Many fertilizer bags are formulated to treat from 2,000 - 5,000 square feet or more, so you might not need to use the entire bag.
Step 3: Use about 1 pound of nitrogen each time you fertilizer, 2 to 4 times per year. If you mulch mow, grass clippings add about 1 pound of nitrogen, so subtract an application or use 3/4 a pound of nitrogen each time.
To figure out how to get 1 pound of nitrogen on your lawn do the following calculation. Look at the first number (also known as the N number) in the N-P-K ratio on your bag. Divide 100 by this number. This number will tell you how much of the fertilizer needs to be applied to 1,000 square feet to supply 1 pound of actual Nitrogen. So if the first number is 8, then 100 divided by 8 is about 12, so you'll need 12 pounds of that product to cover 1,000 square feet. Note that for most solid fertilizers, 1 pound equals about 4 cups of product.
Need more information?
Contact Victoria DeCillo, Groundwater Protection, at 360.753.8463 or via email.
Contact Public Works