Contributed by Christopher Edwards and Martha Rounds, Green Acton Toxics/Pesticides Subcommittee
To take good care of a lawn or garden in Acton, simply buying an off-the-shelf fertilizer and spreading it once or twice a year can be tempting. This guide offers great information on fertilizing your yard in a way that is better for your property and for Acton’s water supply, birds, beneficial insects, and ecosystems. By using this guide, you will be able to use the right fertilizer in the right amount and only when needed.
Whether you are planting perennial plants, trees, shrubs — or even grass — your vegetation needs 17 essential nutrients. Of all the nutrients, nitrogen (N), phosphorus (P), and potassium (K) are required in the largest amounts. Different types of vegetation require different ratios of these macronutrients, referred to as N-P-K ratios. (Each number in these ratios represents the percentage of the element, by weight, in a fertilizer.) A lawn may thrive with an N-P-K ratio of 3-1-2 or 4-1-2, while a garden might need a ratio of 5-10-11, and blooming perennials might need a ratio of 3-1-2.
These ratios should appear prominently on every bag of commercial fertilizer (if you choose to use one). We’ll discuss alternatives to these later. In the fertilizer shown below, the ratio is 4-3-4, which means 4% Nitrogen, 3% Phosphorus (Phosphate), and 4% Potassium (from soluble potash).
Photo credit: Christopher Edwards
Over-fertilizing Is Bad for Your Garden or Yard — and for Acton
It’s important — for several great reasons — to avoid adding unnecessary fertilizer (and the nutrients it provides) to your soil. First, overuse of nitrogen can lead to burned foliage or grass, development of thatch (in a lawn), destruction of important soil microbes, and breeding of unwanted insects. Although phosphate is often touted as key to lush vegetation, excess phosphate can be harmful; for example, it can lead to deficiencies in zinc and iron, causing your plants can wither and die. Too much phosphorus in your soil can also offer some invasive species an advantage over your grass or plants, meaning you could be preferentially feeding your weeds! So serious is phosphate pollution that Massachusetts regulates when phosphorous-laden fertilizers can be used; see more on this below.
Besides causing havoc in your yard, using too much or the wrong type of fertilizer can damage our fragile local ecosystems, potentially putting humans, pets, and biodiversity at risk. This problem is called “nutrient pollution,” defined by NOAA (The National Oceanic and Atmospheric Administration) as “the process [in which] too many nutrients, mainly nitrogen and phosphorus, are added to bodies of water and can act like fertilizer, causing excessive growth of algae.” The Environmental Protection Agency (EPA) has a good primer on nutrient pollution in the home and in agriculture.
Rainfall and watering can cause excess nitrogen and phosphorus to enter the groundwater beneath your property and to run off into storm drains. This nutrient pollution can migrate to ponds, lakes, and streams in and around Acton. When that happens, a process called “eutrophication” can cause the excess growth of algae and other plant life on the water’s surface. This surface plant life depletes the water of oxygen and sunlight, harming (and sometimes killing) underwater plants, fish, and amphibians. In addition, algal byproducts can be toxic to humans and animals.
Photo credit: Christopher Edwards
Better to Test Than Guess
There is only one way to know whether you need to add macronutrients such as nitrogen or potassium (or phosphorus) to your lawn or garden: have your soil tested. A Massachusetts law requires the testing of soil before any application of phosphorus-containing fertilizer (unless it is used in starting a new lawn). At least 10 other states have testing requirements or restrictions on phosphorus use, as well. If you hire a lawn service to fertilize your yard, be sure to ask them to perform a soil test before applying. If they decline, it’s time to look for a service that will test.
You can buy do-it-yourself tests online, but they don’t approach the accuracy of laboratory-based tests. The University of Massachusetts offers a soil-testing service that is quick, inexpensive, and accurate. See below for more on how easy it is to access and use these tests.
Based on the soil samples you submit, the UMass lab will send you a report on the nutrient composition of your soil and how best to amend it for grass, flowering plants, trees, or whatever you specified when submitting your samples. Here are some of the results from two plots tested in different parts of Acton in 2023:
Since the first results showed fairly low levels of potassium and calcium, and borderline low phosphorous, the lab recommended adding a specific amount of potash, limestone, and bone meal or triple phosphate, respectively. Results from the second plot show that phosphorus, potassium, calcium, and magnesium are optimal or in excess for now, so no amendments would be recommended. Unfortunately, the lab does not usually test for nitrogen in these samples, stating that the results would not predict fertilization needs because of wide fluctuations in weather and humidity. Nevertheless, your lab report will have recommendations about the amount of nitrogen you should add to the soil.
Choose Eco-Friendly Fertilizers
Please abide by the Massachusetts regulation on use of phosphorous-containing fertilizers. There are plenty of phosphate-free fertilizer products for use on your yard and garden, including compost, composted manure, and certain slow-release fertilizers. Soil testing will reveal how and when to use such products, so you or your landscaping service can fertilize more effectively without jeopardizing Acton’s precious water resources, ecosystems, and biodiversity. Please consider using non-synthetic products such as compost, composted manure, and/or commercial fertilizers approved for organic growing. Use of synthetic fertilizers (whose ingredients are derived largely from fossil fuels, and which comprise most of the readily available commercial varieties) can confer multiple harms: leaching of nitrogen and phosphorous into groundwater and waterways; making plants less attractive to pollinators; emitting into the atmosphere significant (and increasing) amounts of nitrous oxide, which damages ozone and can trap atmospheric heat roughly 300 times better than carbon dioxide; and doing little-to-nothing to improve ongoing soil health.
Testing Your Soil: A Step-by-Step Guide
If you’ve never considered testing your soil, even the first step — gathering your sample — might be intimidating. We in Massachusetts have access to the UMass Center for Agriculture, Food, and the Environment, which performs soil tests for a nominal fee. This resource makes the testing process manageable and relevant. You can also purchase tests from private companies; some authorities feel that home test kits are not sufficiently reliable.
If you want a reliable way to test your soil, and are not interested in doing detailed research about the process, simply follow these steps. You will end up with the basic information needed to support soil health in your yard, tailored to the types of plants you are growing.
How to Soil Test Using the UMass Soil Testing Service
The steps below are taken directly from the UMass soil testing site. Before you begin: Don’t test after it rains, or within 6–8 weeks after the application of lime or commercial fertilizers. And of course, for your safety, don’t dig in your yard directly after pesticides have been applied. Better yet, don’t use pesticides.
The supplies you will need include the UMass Soil Testing order form; gloves, if you wish; a clean bucket; a trowel, shovel, or augur; a one-cup measure; a piece of paper (newsprint is OK); a small plastic bag; and a small USPS padded mailing envelope.
As the UMass soil testing site notes, the most important step in soil testing is collecting a representative sample and preparing it for the UMass service. To do this, follow these steps:
- Identify the site you want to test. Soil physical appearance, texture, color, slope, drainage, and past management should be similar throughout the area.
- Collect your samples. You will be digging 10–12 narrow holes that are 6–8 inches deep — or 4–6 inches deep if you’re testing only your lawn. Avoid sampling field or plot edges and other “non-representative” areas. Each time you dig a hole, put a scoop of soil from the bottom of the hole into the clean bucket.
- When you finish collecting your 10–12 samples in your bucket, remove stones, twigs, and other debris. Leave lumps of clay or other non-dirt soil.
- Mix your sample soils thoroughly. You can use your hands or your trowel to get the sample well combined.
- Scoop out one cup of soil and place it on a piece of newspaper or other paper so it can dry thoroughly. Let the soil air dry; don’t use heat to dry it.
- Place your dried soil into a small plastic bag. Discard unused soil, perhaps returning it to the holes you dug earlier.
- Fill out your order form. It will ask you what types of plantings you wish to test for; you can choose multiple types. Write a check (remember those? It’s the only way to pay for this test!) for $20. You can receive results by email (faster) or snail mail (costs $2 extra).
- Place your plastic bag of soil, your order form, and your check in the padded USPS bag, and mail.
You will receive results within two weeks, with information on soil health and ways to improve soil condition.
Resources:
• More on N-P-K here and here.
• More on soil testing here.
• UMass Center for Agriculture, Food, and the Environment’s Soil and Plant Nutrient Testing Laboratory