Nantucket Harbor
Island Science

Dreaming of a Green Nantucket

• by Dr. Sarah D. Oktay, Director, University of Massachusetts Nantucket Field Station •

Spring has sprung, the island is filling up with people and warm sunny weather is erasing memories of a long hard winter. This is a perfect time to become aware of how your actions can effect our harbor and ponds. Nantucket’s sandy soils do not grab onto and restrain septic leachate or fertilizer like the rich soils on the mainland. If researchers at the Nantucket Field Station can measure excess nitrate or phosphate in groundwater, marsh water, ponds, and the harbor (and we can), that indicates that you may be flushing money down the drain when you over-fertilize or improperly fertilizer your lawn. Landscapers are now required to be certified to treat lawns using the procedures described in our island’s “Best Management Practices for Landscape Fertilizer Use on Nantucket Island” which can be found in regulations ( which were passed at our Annual Town Meeting in 2012. The complete BMP document including all the committee members and the science that went into the regulations can be found at If you are doing your own lawn maintenance, you should be following the same rules which I will list in detail at the end of this article. All the best management practices are common sense rules that will save you money, reduce tick and mosquito habitat (I am looking at you, over-irrigators) and will ensure that your family has a safe healthy yard to play in while reducing the adverse impacts on our harbors and ponds that promote unsightly and dangerous algae blooms and shade out the eelgrass providing habitat for scallops and other marine life.

Our deep groundwater, located out of the reach of septic systems and fertilizers at a depth of 40 feet or deeper, is very clean and provides a safe drinking water source.  In fact, Nantucket’s location out to sea and away from many mainland sources of pollution like power plants and industrial sites means that our sole source aquifer is safe from most external dangers. But water in the surface parts of the saturated zone around the island (between 0-35 feet or so) in some areas around the island contains evidence of what we flush and put on our lawns.

We can find this evidence when we collect samples of groundwater and measure the contaminants in them. We can also see this contamination when we measure ponds that are downstream of sources.  Instead of exotic dangers like heavy metals or radioactive pollutants, our primary culprits are garden variety hazards such as nitrate and phosphate from leaking septic systems and fertilizer applications.  Wells located only 100-200 feet apart may have very different amounts of contaminants.  Out in the field, we measure nitrate and orthophosphate, which are the more bioavailable (easier to use) nutrient species of nitrogen and phosphorus.  Nutrients are exactly what they sound like: minerals and elements that are needed for growth and normal plant and animal processes in small amounts that, when administered in large amounts, can “overstuff” a pond.  Some of our ponds are having Thanksgiving dinner almost every day!  Pond health is very similar to our health and you can overfeed a pond or harbor by supplying excess “food” in the form of nutrients.  What we try to do is measure where the excess “calories” are coming from and then put the pond on a diet to help it slim down. Some ponds, if they are really “fat” and have stored way too much food, must be liposuctioned by removing the packaged food or fat hanging out in the form of huge algal mats.  But just like removing fat without stopping the intake that got you there in the first place, “liposuction” should be done after the diet is successfully (and permanently) in place.  Not that I am one to be lecturing a chubby pond…who knows, it could be genetic. This summer Hummock Pond will be liposuctioned in the form of harvesting of large submerged aquatic vegetation as recommended by the Nantucket Pond Coalition who have also talked with island conservation groups and the Town of Nantucket’s Water Quality team and obtained a Conservation Commission permit ( A large water based harvester which looks a bit like a boat/lawnmower hybrid will remove some of the plants currently impeding navigation in the pond.

All over the island, groundwater that has been contaminated from septic systems or fertilizers can be 100-1000 time background levels. But in many areas, groundwater levels are refreshingly low, and can be in the range of 0.01-0.1 mg/L for nitrate and phosphate in areas near conservation land or in soil that is effectively filtered the groundwater.  Many homeowners are being more diligent about pumping and inspecting their septic tanks (thanks to the efforts of the Health Department) and reducing unnecessary fertilizer applications so we are seeing reductions in nutrient load in a few areas on island.

Please be proactive and make sure that your landscapers are following the rules, if not, find a different landscaper! If phosphate and nitrate are getting into the groundwater, that is compromising the harbor and ponds and lowering your property value in addition to pouring money down the drain. If you are applying fertilizers yourself, you too must follow the BMPs as they are currently Board of Health Regulations. Save this link to your cell phone so you can remember what is and is not allowed. The BMP regulations apply to professional fertilizer applicators and interested homeowners on Nantucket, excepting commercial agriculture. Landscapers must take a test to be licensed and they reapply for licensure every three years.

Here are some useful fertilizer tips and details on exactly what your landscaper should be using on your lawn from “Fertilizer Application Tips For Homeowners on Nantucket” as developed by the BMP committee:

Fertilizer should be applied for plants to use as quickly and effectively as possible. Excess nutrients will harm Nantucket’s water, therefore only apply soil amendments and fertilizers between April 15 and Oct 15 so that plants can use the nutrients while they are actively growing and not dormant. Do not apply fertilizers before a strong rain that will wash it into water sources and avoid excess irrigation. Avoid wetlands and other areas defined by the Conservation Commission as no-fertilize areas (the Conservation Commission has adopted the BMPs).

On the topic of compost, the BMP reminds us that we are still on Nantucket and our “soil” is different and needs to be treated differently. Many of our amended lawn and garden soils have enough phosphate for plant growth, therefore adding more might harm fresh water ponds and the groundwater. Animal manures and animal-manure-based composts are rich in nitrogen and phosphate; leaf litter composts are less so and are preferred. Native levels of organic matter, OM, are lower here than elsewhere. Compost is important to develop organic matter in soil and is a source of carbon and other nutrients. Compost retains moisture, and hosts beneficial bacteria and insects. The BMP states that leaf litter compost is preferred and to remember that while compost is important for raising organic matter levels, it should be applied slowly. Raising soil organic matter much above native levels can result in nitrogen and phosphorus leaching.

The BMPs also state it is critical to test the soil and see what you need before you add material that will be leached away because the turf or your garden plants cannot use the nutrients (just like overeating adds fat if it the calories are not burned for fuel). Please read all labels when buying and applying fertilizer. Labels list the ingredients as follows: Nitrogen, N, as elemental nitrogen, Phosphorus, P, as P2O5, and Potassium, K, as potash, K2O. All fertilizers whether they are synthetic, organic or hybrids list the amount of the nutrients they contain on the bag, usually as a percent of weight. Also be aware that many fertilizers contain pesticide and herbicides components which is why I advocate that organic pesticide free products be used on lawns in which pets or children may be playing.

The BMP recognized that scientist and soil and plants experts know that nitrogen application limits are needed because excess nitrogen affects marine life. The BMPs state that no more than 3.0 pounds per 1000 square feet of nitrogen can be applied per season for turf. Nitrogen should be applied at two week intervals (or longer) and in quantities of no more than 0.5 pounds per application. In addition, no more than 0.25 pounds per 1000 square feet of quick-release nitrogen is allowed per application. The regulations also state that a single application for trees, shrubs, herbs and other ornamental plantings shall not exceed 0.5 pounds of actual nitrogen per thousand square feet and the annual rate shall not exceed 2.0 pounds of actual nitrogen per thousand square feet.

Phosphate application limits: Excess phosphates affect fresh water life. No phosphorus is permitted unless need is indicated by a soil test. If soil tests show phosphorus is low in the soil, new plantings and moved plantings may receive phosphate. In a nutshell: keep excess phosphorus from lawns, gardens and farms out of the ponds. Our new Best Management Practices (BMP) for the island recommends that no phosphorus be used in any fertilizer unless a soil test shows it is needed. We already have plenty of phosphorus in our sandy soil and excess is not used by the plant and goes straight to the shallow groundwater. Organic fertilizer should also be used sparingly and should contain low phosphorus. Manure may contain a lot of phosphorus so just because something is organic doesn’t mean you should go to town using it. Look at the shampoos and detergents you use and make sure they have no phosphorus.

Effective lawn care can reduce the need for fertilizer. For instance: Let your grass grow longer, 2 ½ to 3 inches long. The plant is healthier and can take up fertilizer more effectively. Long grass stays greener during the heat of summer better. A 3-inch high lawn can take up and use nutrients up to ten times as effectively as a 2-inch lawn. Leave the clippings on the lawn. They equal a pound of fertilizer per 1,000 sq. ft. per year that you do not have to apply. Cut the grass more often. Never remove more than the top 1/3 of the length. Your lawn will be healthier.

Using native plants is a simple way to reduce nutrient inputs to our soils. Site planning and landscape designs incorporating or preserving native plants, which do not require fertilizer, are encouraged. Here are a few native plants that work well on Nantucket:

  • Meadow grasses, including little bluestem and Pennsylvania sedge;
  • Shrubs, including bayberry, inkberry, winterberry, and blueberry;
  • Trees including red maple, tupelo, American holly, and oaks.

Regulations again, which are straightforward can be found here: and the whole BMP is at

The BMP came out of Article 68 which was a regulation/bylaw proposed at the 2010 town meeting as a result of an action items from the Nantucket Harbor Plan that stated that regulations should limit fertilizers inputs into our water. Doug (Smitty) Smith and I brought forward Article 68 and as a result a committee was formed that worked for 2-3 years to develop the BMPs. These are the members of the committee which was comprised of landscape professionals, golf green experts, gardeners, scientists, and conservationists: Lucinda Young, Chair, Peter Boyce, Vice Chair, Lee Saperstein, Secretary, Cormac Collier, Caroline Ellis, David Fronzuto, Bam LaFarge (deceased), Mark Lucas, Wendy McCrae, Michael Misurelli, Richard Ray, Seth Rutherford, Ernie Steinauer, and Jim Sutherland, Administrative Assistant.

Lucinda Young, Chairperson of the Article 68 Work Group wrote an eloquent and effective preface to the BMPs: “The following Best Management Practices Plan (BMP) is broken down into sections that contain comprehensive information on soil fertility and landscape fertilizer use on Nantucket. Sections were drafted by members of the Article 68 Work Group and by landscape professionals of diverse backgrounds and levels of education, expertise and experience. As I read through this document, it strikes me over and over how closely interrelated each aspect of turf and plant dynamics is to soil chemistry, climate, and cultural practices. Reading through the BMP, one section at a time, can be compared to looking at or studying individual trees one by one in the forest. It’s important not to lose sight of the forest, as a whole, but also not to over simplify complex science. The ‘forest’ in this case can be considered not only an individual lawn or garden landscape, but in fact, the whole island. The BMP attempts to explain the complex science of plant and soil dynamics in terms that are accessible to landscape professionals as well as interested homeowners. It reminds us that all is interrelated: climate, water and nutrient cycles, turf, gardens, soil, groundwater, and our ponds, wetlands, and harbors. With the risk of getting lost in ‘the forest’ of the BMP, the following is a summary of key factors that influence correct rates and timing of fertilizer applications to Nantucket’s man-made landscapes.

1- The importance of a soil test in determining and correcting soil pH, nutrient deficiencies, and the amount of organic matter content.

2- Climate: Fertilizers applied to turf or plants when soil temperature is below 55 degrees F are not readily assimilated by plants, and are thus likely to end up in our harbors or ponds, or groundwater, threatening aquatic and human health.

3- The importance of organic matter content in soils and how that influences nutrient availability and ‘builds’ healthy soil.

4- The role of mowing height, not less than 2 inches, and frequency, the one-third rule, in promoting and maintaining healthy turf.

5- The importance of returning clippings to recycle nutrients and increase soil organic matter content.

6- The no-fertilizer option; i.e. natural landscapes where growth is in equilibrium with nutrients from fallen vegetation.

If everyone who applies fertilizers to turf or garden plants on Nantucket applies the information in this BMP to their practices, the threat of landscape-related fertilizers entering ground water, ponds and our harbors should be significantly reduced.”

Parts of this article were previously published here in 2009:

Articles by Date from 2012