Care of Ornamental Plants in the Landscape (B 1065) University of Georgia Extension Most established ornamental plants in the landscape require care to stay healthy and attractive. Regular fertilization, pruning, watering, mulching and pest control are all part of a good landscape management program. This publication provides guidelines for the care of established ornamental plants in the landscape. Low-maintenance alternatives to traditional cultural practices are discussed throughout the publication. 2016-06-16 18:23:55.967 2006-06-02 14:27:08.0 Care of Ornamental Plants in the Landscape | Publications | UGA Extension Skip to content

Care of Ornamental Plants in the Landscape (B 1065)

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Reviewed By Bodie Pennisi

Originally prepared by Gary L. Wade, former Extension horticulturist, and Beverly Sparks, former Extension entomologist

    Introduction

    Most established ornamental plants in the landscape require care to stay healthy and attractive. Regular fertilization, pruning, watering, mulching and pest control are all part of a good landscape management program.

    Some plants, such as annual flowers, roses, red-tip photinia and English laurel, are more demanding than others. Annual flowers and roses must be kept well-supplied with nutrients and water at all times, pruned and groomed routinely, and monitored regularly for pests if they are to flower abundantly. Red-tip photinia and English laurel are very susceptible to leaf spot diseases and demand more care.

    On the other hand, plants such as ornamental grasses, hollies and junipers, when properly planted on a good site, require little care once established and are considered good low-maintenance plants.

    Caring for ornamental plants is more difficult when they are not well-suited to the site selected or when they are improperly planted. Azaleas, for instance, prefer a moist, well-drained soil and shade from the mid-afternoon sun. When planted in poorly drained soil or in full sun without the benefit of irrigation, azaleas become stressed, susceptible to attack from insects and diseases, and require more care. Planting too deeply or too shallowly also causes plant problems.

    Today, the concept of low-maintenance landscapes is more popular than ever before. The idea of putting less effort into the landscape without sacrificing quality and beauty is very appealing to a growing number of homeowners and clients of landscape professionals. By applying lower amounts of fertilizer, water and pesticides to the landscape, you not only help the environment but also save time and money. New concepts in low-maintenance landscaping, such as Xeriscaping (water-efficient landscaping) and integrated pest management (control of pests through the selective use of insecticides and encouragement of natural enemies), are proving that it is possible to have a beautiful landscape while saving time, effort and money.

    This publication provides guidelines for the care of established ornamental plants in the landscape. Low-maintenance alternatives to traditional cultural practices are discussed throughout the publication.

    Start by identifying areas of the landscape that require different amounts of care. A recently planted area, for instance, will generally require more attention than a well-established area. The highly visible public area of the landscape is usually an are where optimum growth is desired at all times, while a secluded, private area requires less maintenance. Once this "zoning" is done and the different levels of plant care are established, landscape maintenance becomes much more efficient and effective.

    Fertilization

    Fertilization is an important part of landscape maintenance, particularly in urban areas where much of the native topsoil is removed during development and subsoil deficient in essential nutrients becomes the new topsoil.

    Unfortunately, fertilization is a rather simple cultural practice made complex and confusing by the wide variety of fertilizer products on the market today -- from "general-purpose" garden fertilizer to specialty products, such as pre-mixed liquid fertilizer concentrates, water-soluble crystals, slow-release fertilizers, azalea/camellia fertilizers and rose specials. Plants generally do not care whether a fertilizer is granulated, liquified, encapsulated, briquetted, pelletized or solubilized! They simply want nutrients in any form they can use.

    Fertilizers, however, differ in nutrient content and release duration. The type of fertilizer you select should be based not only on its cost but also on the types of plants being fertilized, the existing nutrient content of the soil, and the type of growth response desired. Liquid or water-soluble fertilizers, for instance, are often used on annuals and herbaceous perennials immediately after transplanting because their nutrients can be absorbed quickly and used by the plant. Woody ornamentals, on the other hand, store food reserves in their roots and do not have an immediate demand for nutrients after transplanting as short-season annuals do. They benefit from slow-release fertilizers that ensure a supply of nutrients as needed.

    To determine whether a granular fertilizer has slow-release properties, look at the analysis on the back of the bag. Nitrogen listed in the form of ammoniacal nitrogen indicates that the product has some slow-release property. If the nitrogen is listed as being derived from urea, urea-formaldehyde, IBDU (isobutylenediurea), or sulfur-coated urea, the release duration of the product will be increased. Some granular slow-release fertilizers last six to eight months after application.

    Other commonly available slow-release fertilizers on the market include Osmocote granules, Osmocote tablets, Jobe's Spikes, Once, Woodace briquettes, Agriform tablets and Milorganite. These fertilizers generally cost more per pound than general-purpose granular fertilizers such as 10-10-10 or 12-4-8, but they also last longer and don't need to be applied as frequently.

    Organic fertilizer sources such as bone meal, cottonseed meal and animal manures can also be used. Table 1 lists the average nutrient content of several organic fertilizer sources. Compost is another good source of slowly available nutrients.

    Table 1. Average nutrient content of various organic fertilizer sources.
    % Nitrogen
    (N)
    Phosphorus
    (P2O5)
    % Potash
    (K2O)
    Blood, dried
    13.0
    -
    -
    Bone meal (raw)
    3.5
    22.0
    -
    Bone meal (steamed)
    2.0
    28.0
    -
    Cottonseed meal
    6.6
    2.5
    1.5
    Fish scrap (dried)
    9.5
    6.0
    -
    Soybean meal
    7.0
    1.2
    1.5
    Horse manure
    0.7
    0.3
    0.6
    Cow manure
    0.6
    0.2
    0.6
    Pig manure
    0.5
    0.3
    0.5
    Sheep manure
    0.8
    0.3
    0.9
    Chicken manure
    1.1
    0.8
    0.5
    Duck manure
    0.6
    1.4
    0.5
    Source: Soil Fertility and Fertilizers. S.L. Tisdale and W.L. Nelson. MacMillan Publishing Co., 1975.

    Which Analysis Is Best?

    A soil test, available through your county Extension office, is the best way to determine which fertilizer analysis is best for your soil. As a general guideline, most ornamental plants will benefit from a fertilizer having its primary nutrients (nitrogen, phosphorus and potassium [N-P-K]) in a 3-1-2 or 4-1-2 ratio. A 12-4-8 fertilizer, for instance, is a 3-1-2 ratio, and a 16-4-8 fertilizer is a 4-1-2 ratio. Research shows that phosphorus, the middle number in the analysis, is held be soils and does not leach with rains or irrigation as nitrogen or potassium do; so it is usually needed in lower amounts. On new sites where phosphorus has never been applied, a complete balanced fertilizer such as 8-8-8 or 10-10-10 is sometimes recommended.

    When Should You Fertilize?

    Research shows that woody plants actively absorb nutrients from the soil during the growing season and require few nutrients during the dormant winter season (see Figure 1). Therefore, apply fertilizer as soon as the plants begin breaking dormancy in the spring, and avoid fertilizing after the first fall frost, which signals plants to begin resting for the winter.

    graph showin relationship between nitrate uptake efficiency of nonbearing prune trees and their growth cycle Figure 1. The relationship between nitrate uptake efficiency of non-bearing prune trees and their growth cycle. Source; S.A. Weinbaum, et. al., 1986. J. Amer. Hort. Sci. 111(2): 224-228.

    How Often Should You Fertilize and How Much Should You Apply?

    The frequency of fertilization depends on the type of plants being fertilized and the type of fertilizer used. If slow-release fertilizers are used, one application should be sufficient for the entire growing season. If general-purpose granular fertilizers are used, two or three applications may be needed, depending on the fertilizer's slow-release properties.

    When general-purpose granular fertilizers such as 12-4-8 or 10-10-10 are used on newly-planted ground covers, annuals, herbaceous perennials and roses, light applications made at four- to six-week intervals are recommended.

    During periods of limited rainfall or drought, reduce the amount of fertilizer applied and the frequency of application in non-irrigated areas. Fertilizers may injure the roots of ornamentals under drought stress.

    Newly-planted ornamental trees and shrubs will benefit from light applications of fertilizer made during the first growing season after transplanting (Table 2). Uniformly broadcast the fertilizer along the perimeter of the planting hole. Avoid using weed-and-feed fertilizers in the vicinity of newly-planted ornamentals because injury from the herbicide may result.

    Newly-planted 1-gallon size plants will respond to 1 level teaspoon of a 12 to 16 percent nitrogen fertilizer or a level tablespoon of an 8 to 10 percent nitrogen fertilizer applied in March, May and July. Small trees, fewer than 4 feet tall, should receive no more than 1 tablespoon of a 12 to 16 percent nitrogen fertilizer two to three times during the first growing season. Larger trees will benefit from 3 to 4 tablespoons of a 12 to 16 percent nitrogen fertilizer. Broadcast fertilizer along the perimeter of the planting hole. Remember that newly trans-planted ornamentals are under stress while they are trying to adapt to their new location and they can be easily injured by over-fertilization.

    Table 2. Recommended fertilization rates for newly planted ornamental plants during the first growing season (use only one of the fertilizers listed at the rate recommended).
    Application rate1/plant
    Application frequency
    Plant type/size
    12-4-8
    16-4-8
    10-10-10
    1-gallon shrubs
    1 tsp.
    1 tsp.
    1 tbsp.
    March, May, July
    3-gallon shrubs
    2 tsp.
    2 tsp.
    2 tbsp.
    March, May, July
    5-gallon shrubs
    3 tsp.
    3 tsp.
    3 tbsp.
    March, May, July
    Trees under 4 feet
    1 tbsp.
    1 tbsp.
    2 tbsp.
    March, July
    Trees 4 to 6 feet
    3 tbsp.
    3 tbsp.
    5 tbsp.
    March, July
    Trees 6 to 8 feet
    4 tbsp.
    4 tbsp.
    6 tbsp.
    March, July
    Application 100/sq. ft
    Application frequency
    12-4-8
    16-4-8
    10-10-10
    Ground covers, annuals & herbaceous perennials
    0.5 lb.
    0.5 lb.
    1 lb.
    Each 4 to 6 weeks
    1tsp. = level teaspoon; tbsp. = level tablespoon; lb. = pound. When using slow-release or soluble fertilizers, follow label recommendations for application rate.

    The quantity of fertilizer applied on established ornamentals depends on the analysis of the fertilizer used, the area fertilized and the amount of growth desired. Nitrogen controls vegetative growth, so application rates are based on this primary nutrient. Table 3 lists suggested application rates for several general-purpose fertilizers.

    DO NOT OVER-FERTILIZE OR FOLIAR DAMAGE MAY RESULT. To increase the application rate, increase the frequency of application, but do not exceed the amount recommended in Table 3 for each application. Optimum growth fertilization rates (three to five applications) are usually used on annuals, herbaceous perennials, roses and newly established ground covers to encourage their spread. Otherwise, low rates of fertilizer are recommended, particularly if you desire a lower maintenance landscape. As the application rate of fertilizer increases, so does the amount of new growth, which requires more water, more fertilizer and more pruning.

    Table 3. Recommended application rates of various general-purpose granular fertilizers on established ornamental plants in the landscape.
    Source
    Application rate*
    1000 sq. ft.
    100 sq. ft.
    10 sq. ft.
    pounds
    cups
    pounds
    cups
    tablespoons
    10-10-10
    10.0
    20
    1
    2.0
    4.0
    8-8-8
    12.5
    25
    0.5
    2.5
    5.0
    13-13-13
    12-3-6
    6.0
    12
    3/4
    1.5
    3.0
    12-4-8
    12-6-6
    16-4-8
    6.0
    12
    0.5
    1.0
    2.0
    4-12-12
    25.0
    50
    2.5
    5.0
    10.0
    5-10-10
    20.0
    40
    2
    4.0
    8.0
    * This rate will supply 1 pound of actual nitrogen per 1,000 square feet. For optimum growth of young shrubs, ground covers and trees, three to five applications are recommended at 6- to 10-week intervals from March to August. Application frequency varies with the amount of slow-release nitrogen in the product, so consult the label for specific recommendations. Established trees and shrubs will benefit from one to two applications during the growing season. Annual flowers and roses should receive applications at 4- to 6-week intervals from March to August. When using slow-release or specialty fertilizers, follow the manufacturer's recommendation on the container.

    To determine how much fertilizer to apply, first estimate the area to be fertilized. This involves estimating the length and width of a bed in linear feet and multiplying the two numbers to obtain square footage (see Figure 2). Few plant beds are perfectly square or rectangular, so square off the rounded areas to simplify your estimate. Trees growing within a bed can be included in the bed estimate or, if they require special fertilization, estimate their canopy area by measuring the distance from the trunk to the drip line or tip of the branches (this is called the radius). Then use the geometric formula for the area of a circle to calculate the area of the canopy: 3.14 x radius2. For example, if the distance from the main trunk to the drip line of a tree is measured to be 20 feet, the area beneath the canopy is 3.14 x (20 x 20) = 1,256 square feet. See guidelines below for additional recommendations on tree fertilization.

    1,200 square feet in the plant bed in the drawing Figure 2. Question ? Approximately how many square feet are in this plant bed? Answer ? 1,200 square feet.

    Guidelines and Precautions When Fertilizing

    • Broadcast fertilizer evenly over the bed area. Make certain the foliage is dry when fertilizer is broadcast over the tops of ornamentals.
    • If fertilizer becomes lodged in the foliage of ornamentals, brush it off before irrigating.
    • It is not necessary to remove the mulch when fertilizing. Broadcast fertilizer on top of the mulch and water it in.
    • Trees growing in turf areas will obtain nutrients from the fertilizer that is applied to the turfgrass. Do not apply excess fertilizer to turf in an effort to feed trees; injury to the turf may occur.
    • When fertilizing trees, broadcast the fertilizer over an area extending two to three times the canopy spread if possible. Research has shown that tree roots grow far beyond the canopy spread on established trees.
    • Do not concentrate fertilizer in holes drilled under tree canopy. Research shows that broadcast application results in better growth.
    • An effective technique for fertilizing annual flowers is to place a slow-release fertilizer such as Osmocote in the planting hole directly beneath the plant. This not only provides an even supply of nutrients to the plants, it also decrease the number of weeds when compared to broadcast application.
    • Plants growing in shade generally require less fertilizer than those growing in the sun.
    • Plants growing in sandy soils generally require more frequent fertilization than those in clay soils due to nutrients leaching from sandy soils.
    • Avoid using weed-and-feed lawn fertilizers that contain herbicides near ornamental plants.

    Watering

    Most ornamental plants in the landscape, once they are established, can go days or even weeks without supplemental irrigation. In fact, over-watering (water too frequently) is a leading cause of problems with ornamentals. Junipers, for example, are extremely drought-tolerant once they are established, but they cannot tolerate extended periods of excess moisture.

    Your best guide for determining when to water is the plant itself. Wilting or a pale grayish-green color are the most common symptoms in plants needing water. Certain plants in the landscape -- such as annuals, herbaceous perennials, azaleas and rhododendrons -- need more water than others. By watering only those plants that need water, you not only will save water, time and money, you also avoid watering plants that do not need a lot of moisture.

    Drip irrigation saves water Figure 3. Drip irrigation saves water in the landscape and is ideal for ornamental plants. Do-it-yourself systems are available at most garden centers and are easy to install.

    To avoid run-off and water loss, apply water slowly to the base of the plant using a hand-held hose, drip or trickle irrigation, micro-sprinklers, or an ooze hose. Do-it-yourself irrigation systems, available from most garden centers, use 30 to 50 percent less water than sprinklers, and they can be attached directly to outdoor faucets.

    The amount of water needed by an ornamental plant depends on the type of plant, the soil type, the amount of existing moisture in the soil, and the time of year. As a general rule, 6 gallons of water per 10 square feet of bed area or canopy area will saturate most soils to a depth of about 12 inches (the area containing 80 percent of the roots of most ornamental plants). Because water moves readily within the plant, you do not need to water the entire root zone. Twenty-five percent of the root area can absorb enough water for the entire plant.

    The best time to water is at night or in the early morning. As much as 30 percent of the water applied during midday can be lost to evaporation accelerated by the sun.

    Hydrogels (water-absorbing polymers), sold in garden centers under several different trade names, are popular products on the market. They absorb several hundred times their weight in water and release it slowly, as needed, to the plant. Research at The University of Georgia shows hydrogels may provide a significant growth benefit to summer annuals in non-irrigated soil.

    Mulching

    Mulches are a vital part of the Southern landscape. They hold moisture in the soil, help prevent weed growth, inhibit certain soil-borne foliar diseases, and insulate the roots of plants from temperature extremes during summer and winter. Mulch also provides a buffer zone between the turf and woody ornamental plants and helps prevent trunk injury from weed trimmers and lawn mowers.

    The best mulch is organic, fine-textured and non-matting. Examples include pine needles (commonly called pine straw in the South), pine bark mini-nuggets, hardwood chips and cypress shavings. Fall leaves are an excellent and economical mulch and add valuable humus back to the soil as they decompose. Pecan hulls, a by-product of the pecan industry, are used successfully as mulch in south Georgia. Grass clippings are not a good source of mulch because they tend to mat down and inhibit the flow of water and nutrients into the soil. They also my introduce weeds into ornamental plantings. Inorganic mulches such as rock, gravel and marble are good soil insulators, but they absorb and re-radiate heat in the landscape, increasing water loss from plants. Limit their use to shady areas of the landscape.

    Apply mulches 3 to 5 inches deep in an area extending beyond the canopy of the plant if possible. A small ring of mulch around the trunk provides little benefit to the plant.

    Organic mulches such as pine straw or pine bark break down and decompose over time and should be replenished at least once a year.

    Avoid placing plastic film under mulches; it prevents water, nutrients and oxygen from reaching the roots of the plant. Geo-textile (landscape fabric) can be used instead of plastic film under mulch. It allows water, nutrients and oxygen to reach the roots of plants and prevents the growth of some weeds. For best results, install landscape fabrics on weed-free ground and avoid getting soil on top of the fabric.

    Landscape fabric Figure 4. To install landscape fabric, roll it out over the top of newly planted shrubs, cut an X in it the size of the plant canopy, and push it down over the plant. Avoid gaps in the fabric by overlapping the strips of fabric 1 to 2 inches.

    Pruning

    Ornamental plants in landscapes are pruned for many reasons. We usually prune plants to achieve or maintain a certain size or form. At other times, we prune to remove old, diseased or damaged wood in an effort to promote vigorous new growth, flowering or fruiting.

    Two basic pruning techniques are used to prune ornamental plants -- heading and thinning. Heading (also called heading back) refers to the non-selective removal of branches; thinning is the selective removal of branches back to a side branch or main trunk. Shearing is a form of heading.

    Figure 5. Thinning (right) results in an open canopy, improved air circulation and natural shape; shearing (left) encourages a dense outer canopy and unnatural form.

    Thinning is best for most ornamental plants because it opens up the plant canopy, increases air circulation within the plant, and results in a natural growth form. Shearing is frequently done on small-leaf evergreens such as boxwood and Japanese holly. Shearing is an efficient pruning technique, but it causes a thick outer canopy and loss of natural form.

    If low-maintenance is your goal, keep shearing to a minimum in the landscape. Once you start shearing plants, you will have to shear them more frequently to keep them looking good. Selective thinning of branches once or twice a season is much less labor-intensive than monthly shearing.

    Two ornamental plants in the landscape that ar

    Status and Revision History
    Published on Oct 1, 2001
    Re-published on Feb 26, 2009
    Reviewed on Feb 16, 2012
    Reviewed on Feb 16, 2016