Header for Integrated Pest Management of the University of Connecticut

Fertilization of Trees, Shrubs, Vines and Groundcovers

Plants grown in soils with adequate nutrient levels are more likely to survive a stress period (drought, severe winter, insect or disease attack) than plants grown in soil with inadequate nutrient levels. Fertilizer, however, will not overcome poor cultural conditions such as inadequate light; water logged, compacted or droughty soil; poor plant selection; poor site selection, air pollution; misuse of pesticides, etc.

The old adage ‘a little does a good job, a lot more will do a much better job’ does not apply with fertilizers UNLESS a soil test indicates there is a greater need. Plants growing well may not need any additional fertilizer and so should not be applied routinely. This is particularly true when organic material (compost, leaf litter, etc) is applied to the planting. As the material decomposes nutrients are released into the soil and available to the plants.

Fertilization of Plant Groups

Tree Fertilization

Traditionally, trees in the landscape were fertilized by placing the fertilizer in holes that were drilled or punched into the ground. The reason was to place the fertilizer below the competing grass roots. Research has shown that most of the tree's roots are in the upper six to twelve inches of soil. Therefore, the fertilizer placed in holes was below much of the root system. Also, the distribution of the fertilizer was poor because of the limited root contact with the fertilizer.
The root system of a tree can spread one and one half to two times its height. For example, a tree with a height of 40 feet could have a root spread of 60 to 80 feet. This means the roots will spread 30 to 40 feet away from the trunk. This puts a large percentage of the fine feeder roots well beyond the drip line, which traditionally has been the location of fertilizer added by the hole method.

The use of solid sticks of fertilizers that are pounded into the ground has the same disadvantage as fertilizer placed in holes-there is limited root contact.

An improvement of the hole method is to pump a fertilizer solution into the ground using a feeding needle. The pressures used improve the dispersal of the fertilizer. However, the fertilizer material is often placed twelve or more inches below the surface. An advantage to this method is the loosening of compacted soils.

The preferred method of fertilizing is to spread the fertilizer on the surface over the entire root system of the plant. This allows more of the root system to pick up the nutrients and eliminates zones of high fertilizer concentration which can damage the tender feeder roots. Trees planted in regularly fertilized lawns will probably not require additional fertilizer.

Ericaceous Plants

The ericaceous plants (rhododendron, azalea, laurel, Pieris, Andromeda. etc.) are shallow, fibrous-rooted plants that can be damaged by heavy applications of fertilizer. Apply only the lower rates of fertilizer for plants of this group. An important cultural practice that is often neglected for this group of plants is maintaining the soil's organic matter content. This is easily accomplished by adding an inch or two of organic mulch every year or so. If the mulch is composted material which contains some manure, it will not be necessary to apply any additional fertilizer.

Shrub Fertilization

The root system of most shrubs is located in the area under the plant and extends a few feet beyond the spread of the branches. Therefore, the fertilizer should be broadcast in this area. Avoid injury to the plant by keeping the fertilizer a few inches from the stem. The amount of fertilizer to apply is calculated from the table after measuring the area covered by the plants.

Vines

A vine will "travel" a long distance from where it was planted alongside a wall or under a trellis. The roots radiate in all directions from the point where the stem emerges from the ground unless the vine is planted against a building or some structure that restricts the growth of the roots. Stay at least one foot away from the stem when broadcasting the fertilizer. Cover an area at least 10 ft. x 10 ft. (100 sq. ft.) around the stem. If the ground is bare or planted with shrubs, scratch the fertilizer into the soil to a depth of 1/2 to 1 inch. Vines growing in or near a regularly fertilized lawn will probably not require additional fertilizer.

Groundcovers

Determine the area of the groundcover bed. Broadcast the amount of fertilizer evenly over the area. Apply the fertilizer when the foliage is dry to prevent injury. Fertilizer sticking to wet foliage can cause "burning", and it should be brushed or hosed off.

Fertilizers

fertilizer

The Fertilizer Bag Label

All fertilizer containers have a series of three numbers called the fertilizer grade or analysis, which lists the percentage of nitrogen as N, phosphorus as P205 and potassium as K20. For example, a 100 lb. bag of 10-6-4 will contain 10 lbs. of N, 6 lbs. of P205 and 4 lbs of K20. In a 50 lb bag there would be 5 lbs. of N, 3 lbs. of P2O5 and 2 lbs. of K2O.

 A fertilizer containing all three nutrients (N, P205, K20) is referred to as a complete fertilizer. An incomplete fertilizer contains one or more nutrients, which may include one or two of the macro-nutrients and/or one or more of the micronutrients.

The fertilizer label will indicate whether the material is slow-release, meaning the nutrients are released into the soil over several weeks or months, or quick release. There are many commercial fertilizers that are slow-release as well as compost and most organic materials. Slow release materials help reduce, but do not eliminate, the chances of over-dosing the plant. Follow label rates or soil test recommendations.

Compost and manures should be tested to determine the nutrient analysis prior to application. This is done at university analytical labs as well as companies that provide the material.

Substituting Fertilizers

When purchasing fertilizer, it is more important to look at the fertilizer grade/analysis than the brand. Because of this, it is possible to substitute one fertilizer for that of another as long as the ratio of nutrients is the same or similar. For example, 10-20-20 (ratio of 1-2-2) can be used in place of 5-10-10 (ratio of 1-2-2). An important adjustment must be made, however. The 10-20-20 contains twice as much N, P205 and K20 as 5-10-10. Therefore, 10-20-20 should be applied at half the rate suggested for 5-10-10.

Weight of Fertilizer

The tables in this bulletin give fertilizer guidelines in pounds. To estimate small or intermediate amounts of fertilizer, the following fact is helpful: one level unpacked cupful of 10-10-10, 10-6-4, 5-10-10 or 5-10-5 weighs approximately 1/2 pound.

Fertilizer Application Notes

When to Apply Fertilizer

Fall (late September through mid-October) is the preferred time to fertilize woody plants (trees, shrubs, vines and groundcovers) except for materials containing nitrogen. Early spring, before growth starts, is the next best time for all nutrients including nitrogen. Fertilizing from July through mid-September should be avoided unless the plant is under severe stress due to a nutrient deficiency. The new growth that results from fertilizing during this period often does not harden before the onset of winter, and the result is tip dieback of the new growth.

Avoid applying fertilizers during periods of drought. Water is needed to move the nutrients into the plant. There is also the risk of burning the plant roots.

Avoiding indiscriminate fertilizer applications reduces environmental problems that may result from fertilizer leaching beyond the plant root zone and the chance of fertilizer movement off site.

How Much Fertilizer to Apply

When choosing fertilizers for woody plants use the ratio of 3-1-1 or 3-1-2. Nitrogen is the material that is used in the greatest quantity. The fertilizer recommendations in the table show varying ranges of fertilizer to apply. The smaller amount in a given range should supply enough nutrients for maintenance and adequate growth. The larger amount in a given range will result in more growth. This may be desirable for plants that have not reached the desired or mature size. The larger amount is undesirable if the plant has reached sufficient size. Flowering trees and shrubs (crabapple, dogwood, rhododendron, etc.) should receive the smaller amount of fertilizer in a range to avoid lush vegetative growth at the expense of flower bud formation. Flower bud formation is essential if flowering is to occur the following season.

Other factors to consider when determining the amount of fertilizer to use include:

Watering After Fertilizing

Ideally, fertilizer should be applied just before a heavy rain is predicted so that the fertilizer will wash into the soil. Irrigate the fertilizer area with about 1/2 to 1 inch of water if no rain or only a shower is forecast. Measure the amount of water being applied by placing several cans across the sprinkler pattern. It normally takes one to two hours to deliver one inch of water.

Other considerations

Where the tree or shrub has overgrown a walk, a driveway, rock outcropping or other barrier or structure, reduce the amount of fertilizer applied in proportion to the area covered by the walk, etc. Do not use fertilizer containing broadleaf weed killers (herbicides) near or under woody plants.

Fertilizer Recommendations for Trees, Shrubs and Groundcovers
 

Deciduous Trees, Shrubs, Groundcovers and Vines

Evergreen Trees and Shrubs; Narrow-leaf Evergreens, Rhododendrons and Azaleas

Fertilizer

Lbs. of fertilizer per 100 sq. Ft.

Lbs. of fertilizer per 100 sq. Ft.

10-6-4 or 10-10-10

1-2

1/2-1

5-10-10

2-4

1-2

5-10-5

2-4

1-2

Description: treefert.fig

Description: trefert2.gif

Additional sources:

Fertilizing Trees, UMass.

References:

Appleton, B. and K. Kaufman. 2009. Fertilizing Landscape Trees and Shrubs., Virginia Cooperative Extension.

Neal, C. 2000. Fertilizing Trees and Shrubs. UNH Cooperative Extension.

Morton Arboretum. 2011. Fertilizing Trees and Shrubs.

Prepared by: Edmond L Marrotte, Consumer Horticulturist

Updated by: Mary Concklin, IPM, University of Connecticut. 2011

The information in this document is for educational purposes only.  The recommendations contained are based on the best available knowledge at the time of publication.  Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.  The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.



Footer for Integrated Pest Management of the University of Connecticut