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Nutrition, Soils, Fertilizers and Compost

The Basics of Plant Nutrition and Fertilizers

Although a general principle of sustainable landscaping is to lower inputs, sometimes it is necessary to use fertilizers in a landscape. When to apply fertilizer, where to apply it, and how much to apply are the keys to benefiting the landscape while impacting the environment as little as possible. The goal of any fertilization program is to provide nutrients needed by plants to sustain healthy growth and as defense against insects, weeds, and diseases. There are seventeen macronutrients (required in relatively large amounts) and micronutrients (required in relatively small amounts) that required by plants. Nitrogen (N), phosphorus (P) and potassium (K) are most critical with nitrogen being required in the largest amounts. N, P and K are identified in their percentages by weight in the analysis on the fertilizer label.

Note: All chemicals should be applied according the manufacturer's recommendations on the label. Remember: the label is the law.

Nitrogen (N) in plants is critical to amino acids, proteins, and chlorophyll. It is required in very large amounts and is very mobile in the soil, making it the nutrient that requires replenishment most often. Plants deficient in nitrogen will have characteristic yellowing (chlorosis) of the leaves starting with the older leaves. Chlorosis will start at the leaf tip and progress down the leaf midrib, and growth will slow due to reduced protein synthesis and photosynthetic enzyme activity. Nitrogen deficiency may also mimic herbicide damage. Over-fertilizing with N can also cause a decline in plant health exhibited in excessive shoot and leaf growth, reduced root growth, low plant energy reserves, and increased susceptibility to environmental stresses and some diseases. Because it is a mobile nutrient, excess nitrogen can leach through the soil and into the ground water. From there, it is carried to drinking water sources in the form of nitrates, and into lakes and streams where it reduced water quality for aquatic wildlife.

Phosphorus (P) plays a significant role in respiration - the production of energy-rich compounds in plant cells called ATP and ADP. It is also important to the development of nucleic acids, enzymes, and phospholipids. Phosphorus promotes early plant vigor and stimulates early root growth. A phosphorus deficiency is noted by a dark, greenish-purple color change to foliage, especially in the leaf margins. Contrary to nitrogen, phosphorus moves very little in the soil, binding tightly to soil particles. Because of this, soils that are high in phosphorous will sustain plant growth without additional applications of phosphorus fertilizers. Leaves and other organic yard wastes are the primary sources of excess phosphorus in surface waters which causes algae bloom. If left on hard surfaces such as driveways, sidewalks, and gutters, phosphorus can leach from these wastes into the storm sewer system and eventually into surface waters. Therefore, it is important to rake, remove and compost grass clippings, fallen leaves, and other yard waste from hard surface areas.

Potassium (K) is important in enzyme activation, transpiration, osmosis, and the opening and closing of the stomates on plant foliage. Potassium deficiency symptoms include mottled or chlorotic leaves with small necrotic spots at the leaf tips and margins. Chlorosis starts at the lower leaf margins and progresses upward. Plants with potassium deficiency may also have poor drought tolerance and weak stems. Potassium is held on the surfaces of soil particles and moves little in most soils; however, it can gradually move out of the root zone in very sandy soils. Soils naturally high in potassium do not require supplemental fertilization.

Soils (FUTURE)

Compost (FUTURE)

Fertilizers: The do's and don'ts

Do... Don't...
amend soil with a slow release fertilizer prior to laying new sod; apply fertilizer to plants during dormancy;
amend soil with peat and compost for improving soil structure; apply fertilizer to impervious surfaces including frozen ground;
remove yard waste including fallen leaves and grass clippings from gutters and other hard surfaces; apply fertilizer directly or inadvertently in or near surface waters;
follow all instructions for application of fertilizers listen on the label of the product; forget to use safety equipment such as dust masks, eye protection, gloves and rubber boots when applying fertilizer;
work on a hard surface when filling fertilizer equipment so spills can easily be cleaned up; apply fertilizer after late in the growing season as it may encourage new plant growth that will be killed off when the cold months arrive;
know and understand how your fertilizer equipment works; direct grass clippings into the street when mowing;
shut valves and gates when not fertilizing; apply fertilizers unless absolutely necessary; have your soil tested; target areas that need specific amending;
leave a buffer zone of natural, unmanaged vegetation between landscapes and the shoreline of a lake, river, wetland, stream or pond. forget to know how to get help fast in the event of an accidental inhalation or spill.

To calculate how much fertilizer you will need for a given area, see Calculating Fertilizer Rates from Soil Test Recommendations.

Some plants, such as herbs, typically require little if any fertilization. Grown for their essential oils that provide flavor and fragrance to food and products, herbs that are fertilized produce foliage that tends have lower levels of these oils. Thus, their taste and fragrance is decreased. Landscape and non-turf grasses also do not usually require applications of fertilizers since excess nitrogen will cause the grasses to become floppy and not maintain their upright characteristic. Nutrient requirements should be determined by having the soil tested and observing the foliage color. If the leaf blades are not their normal healthy green color, the plant may need an application of nitrogen or one of the other essential nutrients, or it may indicate a lack of oxygen in the root zone due to poor drainage or excessive irrigation. Cool soil temperatures can also reduce nutritive uptake.

Organic Fertilizers (FUTURE)

Inorganic Fertilizers (FUTURE)

Salt Tolerant Plants

Salt has been used as a de-icer on sidewalks, roadways, highways, and driveways for many years. The salt used is usually sodium chloride (NaCl), a combination of elements that are not beneficial to plants. De-Plants located along de-iced hardscapes often suffer a certain amount of salt damage due to spray from passing vehicles, snow removal, and leaching. According to Professor Carl Rosen of the Department of Horticultural Science, salt leaches into the plant's root zone where it blocks the plant's physiological mechanism to absorb water. The result is a condition called "physiological drought" in which water molecules are held tightly to salt ions. Symptoms of physiological drought include stunting, stem and bud dieback, leaf burn, discolored foliage, and premature leaf drop.

Homeowners can prevent these conditions by using less salt and targeting areas of high-risk such as slopes and hills, and sharp curves. Salt should also be mixed with an abrasive material such as sand and users should wait to apply salt until after snowfall and snow removal. There are also alternatives to salt that are less damaging to plants: calcium chloride, magnesium chloride, etc. For a complete list of de-icing alternatives, see Delahaut and Hasselkus' online article, Salt Injury to Landscape Plants, from the University of Wisconsin Extension Service. Once warm weather has set in, salt levels in the soil can be reduced significantly by watering the areas well to leach salts from the root zone.

When planting herbaceous plant materials along walkway or driveway where salt is used to de-ice in winter, it is important to select plants with high tolerances to salt.

Herbaceous plants with high salt-tolerance

Scientific name Common name
Aquilegia micrantha Cliff columbine
Calamagrostis acutifolia 'Karl Foerster' Karl Foerster reed grass
Dianthus pulminarious 'Allwood' Helen Allwood pinks
Dianthus x 'Little Boy Blue' Little Boy Blue pinks
Dianthus gratianopolitanus Spotti pinks
Lotus corniculatus Bird's foot trefoil
Machaeranthera xylorrhiza Common woody aster
Schizachyrium scoparium Little bluestem
Waldsteinia fragarioides Barren strawberry

Herbaceous plants with moderate salt-tolerance

Scientific name Common name
Artemisia schmidtiana 'Silver Mound' Silver mound festuca a
Festuca 'Elijah Blue' Elijah Blue festuca grass
Hosta spp. Hosta
Hemerocallis 'Stella d'Oro' Stella d'oro daylily
Hemerocallis fulva Tawny daylily
Helleborus orientalis Lenten rose
Heuchera micrantha 'Palace Purple' Palace Purple coral bells
Oenothera caespitosa Evening primrose
Sedum spectabile 'Autumn Joy' Sedum 'Autumn Joy'
Sphaeralcea coccinea Prairie mallow
Yucca glauca Soapweed


Clemson University Cooperative Extension, "Groundcovers", HGIC 1100, Marjan Kluepfel and Bob Polomski, Home and Garden Information Center. October 1999.

Colorado State University Cooperative Extension, online information, "Salt Tolerance of Temperate Zone Plants", April 13, 1997.

Rosen, Carl, Professor and Interim Head, Department of Horticultural Science, email correspondence, May 31, 2002.

Texas Natural Resource Conservation Commission, "Mulching and Composting", GI-036, September 1996.

University of Minnesota Extension, "Composting and Mulching: A Guide to Managing Organic Wastes", BU-3296-GO, Carl Rosen, Thomas R. Halbach, and Robert Mugaas. Revised 2000.

University of Minnesota Extension, "Soil Test Interpretations and Fertilizer Management for Lawns, Turf, Gardens, and Landscape Plants", BU-1731-GO, Carl Rosen, Peter M. Bierman, and Roger D. Eliason. 1998.

University of Minnesota Soil Testing Laboratory.

University of Minnesota Extension, "Making Compost", INFO-U publication #277, David Whiting and Mark Doneux. Revised 2000.

University of Minnesota Extension, "Structures for Backyard Composting", FS-5553-GO, Robert J. Mugaas and Thomas R. Halbach. Revised 1998.

University of Minnesota Extension, "Simple and Successful Vegetable Farming: How to Keep Your Soil Healthy", FO-7620. 2000.

University of Minnesota Extension, online publication, "Calculating Fertilizer Rates from Soil Test Recommendations".

University of Missouri-Columbia, "Growing Herbs at Home", agriculture publication G06470, David H. Trinklein and Ray R. Rothenberger, Department of Horticulture. Reprinted August 15, 2000

University of Nebraska Cooperative Extension, "Ornamental Grasses in Nebraska Landscapes", G96-1310-A, NebGuide, Donald Steinegger, John Fech, Dale Lindgren, and Anne Streich. Revised May 1999.

University of Wisconsin Extension, "Salt Injury to Landscape Plants", A2970, K.A. Delahaut and E.R. Hasselkus. 1999.

Zimmerman, Bruce, "Salt Tolerant Plant Material", Hort-Pro Online Magazine, M.K. Rittenhouse & Sons Co., December 6, 2001.

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