Fertilizing Landscape Plants             OH 22

Leonard Perry, Extension Professor

The fertilizer needs of plants vary with the kinds of plants selected and the condition of the soil in which they are
grown. General recommendations are provided as a guide for supplying plants with necessary nutrients. A soil test can
supply more specific recommendations. Consult your local Extension office or local lawn and garden dealer for soil
sampling procedures and mailing kits.

Nutrients can be supplied to plants from either organic or chemical fertilizers. The nutrients in organic fertilizers are
generally in more slowly available forms, while those in chemical fertilizers are more quickly available to plants.

A "complete" chemical fertilizer, containing nitrogen, phosphate, and potash is often a practical way to provide needed
nutrients to many plants. The numbers on the bag give the percentage of these three nutrients respectively. For
example, a 5-10-5 fertilizer contains 5 percent nitrogen (N), 10 percent phosphate (P₂O₅), and 5 percent potash
(K₂O). Usually some minor elements such as sulfur and iron, which are needed by plants in very small amounts, occur
in complete fertilizers as impurities.

Some manufacturers supply complete fertilizers with some of the nitrogen in slowly available forms. These release
nitrogen over a longer period of time than the quickly available inorganic forms. The label may refer to this as "organic"
or "slow-release" nitrogen. Superphosphate provides phosphate to plants and is often incorporated into the soil at
planting time to encourage good root growth.

Organic fertilizers include fresh and dried animal manures, blood meal, cottonseed meal, and steamed bone meal.
Pulverized rockpowders, such as rock phosphates and greensand, can be used to supply phosphate and potash.
Because of their low solubility, these pulverized rock powders need to be applied at relatively high rates to supply
plants with adequate amounts of nutrients.

Shrubs, Vines, Ground Covers, Perennial Flowers: Most deciduous and evergreen shrubs, ground covers, and
perennial flowers do best if grown in cultivated or mulched beds. Regular fertilization will increase vigor and flowering.

One to two fertilizer applications per season are needed. Broadcast 1 pound (2 1/2 cups) of 5-10-5 (or a fertilizer
with an equivalent amount of nitrogen) over 100 square feet of bed in early May or mid-October. On sandy soils,
where available nutrients are easily leached away, two applications per year may give best results.

Slow-release or organic fertilizers should be applied in late May or early June after the ground has warmed up.

Garden Roses and Annual Flowers continue to grow vigorously throughout the summer and benefit from a constant
supply of nutrients. Supplement initial soil preparation and/or organic fertilizers by spreading 1/2 cup of 10-10-10 (or a
fertilizer with an equivalent amount of nitrogen) per 100 square feet. Use the higher rates for older plants or when
mulch is used. Also, apply 1 to 1 1/2 pounds of 0-20-20 per 100 square feet. Broadcast the fertilizer in early spring,
but keep it 12 to 18 inches away from plant stems. Complete acid-reacting fertilizers that supply equivalent amounts of
nitrogen in the ammonia form may be substituted. Several azalea fertilizer mixtures are available on the market.

Plants in pots, window boxes, urns, and planters usually require frequent fertilization or the use of slow-release or
organic fertilizers because frequent watering, followed by rapid drying, tends to leach out available nutrients.
Slow-release commercial fertilizers, composted manures, and dehydrated manures are useful in the soil mixture to
provide a steady source of nutrients. A water-soluble fertilizer such as 20-20-20 and similar analyses can be used to
supplement slow-release forms.

Established evergreens, shade trees, and shrubs growing in lawn areas may receive sufficient fertilizer from proper
lawn fertilization. For trees in non-lawn areas, measure the trunk diameter 4 1/2 feet above the ground. Then apply
fertilizer starting 2 1/2 feet out from the trunk to a distance extending 25 percent beyond the spread of the branches.
Use a complete fertilizer such as 10-10-10 or a fertilizer with an equivalent amount of nitrogen. For trees up to 5
inches in diameter, broadcast 1 pound of fertilizer per inch of trunk diameter evenly over the area; for trees over 5
inches in diameter, apply 3 pounds per inch of trunk thickness. Where roads or sidewalks take up a portion of the
area, reduce the amount of fertilizer accordingly. If the rate indicated is in excess of 10 pounds per 100 square feet of
area, apply one-half the amount in two equal portions at 4- to 6-week intervals.

Another method is to put the fertilizer under the soil surface directly into the tree root zone. Use a crowbar or earth
drill to make holes at 18-inch intervals to a depth of 10 to 18 inches. Treat an area starting one-half the distance from
the trunk to the branch perimeter and continue a few feet beyond the branch perimeter. Put about 1/4 cup of
10-10-10 fertilizer or a fertilizer with an equivalent amount of nitrogen into each hole, then fill the hole with water
several times. After the water drains away fill the holes with soil.

Soil pH: The term pH refers to a measure of soil acidity (sour) or alkalinity (sweet). Numbers below 7 are acid; those
above are alkaline. A soil test will include pH. New England soils commonly vary from pH 4.5 to 7.5. Most plants do
best in soils with a pH of 5.5 to 6.5. You may need to change the pH to get desirable growth of plants in your garden.

Adjusting pH: Fertilizers and mulches may lower the soil pH. Most plants (except acid-loving plants) benefit from the
addition of ground limestone. Applying dolomitic limestone, which supplies magnesium as well as calcium, is an easy
way to raise the pH of an acid soil. The amount of limestone needed depends on the soil type and the plants you want
to grow. Your soil test will determine the amount of lime needed. You can apply lime at any time, but it is usually easier
to do it when you are preparing the soil for planting. Lime is most effective if incorporated into the soil rather than
spread on the surface.

The acidity of soil may be increased (pH lowered) when necessary by incorporating large amounts of acid-reacting
organic matter, such as peat moss, shredded sphagnum moss, peat humus, oak, pine or hemlock leafmold, sawdust, or
bark. However, pH may be lowered more effectively by incorporating 2 to 4 pounds of sulfur per 100 square feet.

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Lawrence Forcier, Director, UVM Extension System, Burlington, Vermont. University of Vermont Extension System and U.S. Department of Agriculture cooperating, offer education and employment to everyone, without regard to race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status.

Last reviewed 2003