A. General Guidelines for Compost Application

will also be dependent upon the compost feedstock and texture classification of

the soil being amended. Coarser compost particles (wood based) located on the

soil surface can impede seed-to-soil contact, reducing grass seed germination rate.

Compost should also meet all applicable state and federal health and safety

standards. Sharp objects and fragments (i.e., glass and metal) should be avoided,

man-made inerts should be minimized, and the product should be free of weeds

(Alexander, 1995).

Mulching and erosion control — The type of compost used as a decorative

and/or functional mulch may vary widely since mulches have numerous functions:

agronomic (e.g. reduction of soil temperature fluctuation, reduction of moisture

stress), grounds management (e.g., weed control), and aesthetic. For some, the

aesthetic characteristics of the mulch are the most significant factors; those factors

are the most subjective. An aesthetically acceptable mulch is consistent in appearance, contains no foreign matter, and has minimal odors. In some parts of the U.S.,

dark mulches are preferred, while light colored (cypress) or red mulches are preferred

elsewhere.

The particle size of the product may vary since some end users are accustomed

to fine mulches, and others are accustomed to coarse, woody mulches. Coarser

mulches may be more effective in reducing weed growth, preventing wind erosion,

and allowing the infiltration of surface-applied water (Stewart and Pacific, 1993).

The soluble salt content of the compost mulch may also vary; however, soluble salts

leached from the mulch can cause detrimental effects to more salt sensitive crops,

such as geraniums (Pelargonium sp.). The stability of the compost used may vary

widely, as everything from fine, well-composted materials to uncomposted wood

chips are used as mulch. Composts containing high salt levels, high NH4 levels, or

other phytotoxins should not be used if crops are to be established on the mulched

site soon after application (Alexander, 1995).

To improve the weed control capabilities of the compost mulch, various plastic

products, landscape fabric, newspaper, or even herbicides may be applied before the

mulch is applied. Because a stable compost mulch will readily supply mineral

elements, many plants will not require additional nutrition during the first 12 months

following mulch application. This is particularly true with composts rich in N.

Additional mineral elements, particularly N, may be necessary where less stable or

carbonaceous compost products are used (Alexander, 1995).

Compost used for erosion control should be slightly coarse to coarse. The particle

size may vary widely. If the compost contains some particles 1.3 cm (1/2 in.) in size

or greater, these coarser particles will overlap on the soil surface, creating a stable

mat which resists water and wind erosion. A maximum compost particle size has

not been established; however, very coarse products may be more difficult to apply

and problematic if the slope is to be landscaped or seeded. Fine compost may tend

to be more affected by wind erosion, but may be able to more effectively absorb

moisture. Caution should be employed when using nutrient-rich compost products

in or adjacent to environmentally sensitive areas or where water quality concerns

exist. Only yard debris compost, compost made from uncontaminated wood wastebased materials, or well-stabilized biosolids compost are recommended at this time.



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If biosolids composts are used, they should contain N in a primarily water-insoluble

form, low in nitrates (Alexander, 1995).

Planting backfill mix amendment — Stable composts with relatively high plant

nutrient levels are desired, as such composts may eliminate the need to add fertilizer

during planting. If fertilizers are to be applied at planting, only slow-release forms

are recommended. Where salt-sensitive ornamental crops are planted, up to half the

recommended fertilizer rate should be applied. The soluble salt content (concentration) of compost used in backfill mixes may vary. However, the preferred soluble

salt content of the finished backfill mix should be 3 dS·m–1 or less. Maximum salt

tolerance levels are soil and species dependent. Soluble salts should not be a significant problem with most woody ornamentals. However, care should be given when

bare root, ericaceous, and other salt-sensitive crops are planted. The quality of the

compost used in this application depends upon the specific crop being planted, the

age and sensitivity of the plant, and the type of native soil in which it is blended.

In this application, however, the higher quality the compost, the better (Alexander,

1995).

Soil blend component — Compost used for blending must be moderately to

highly stable and must pass growth screening tests. If the blended topsoil is to be

aged before end use, a moderately stable compost may be used. The use of coarser

composts may necessitate the need to screen the finished topsoil blend. The soluble

salt content of the compost used in the soil blend may vary; however, the soluble

salt content of the finished blend should not surpass the maximum salt tolerance

levels of the crop(s) to be planted in the soil blend. Although not typically a concern,

composts which contain large quantities of very fine particles (passing through 1

mm sieve) may reduce the porosity of the soil blend (Alexander, 1995).

More specific data are needed that compare the effects of particular compost

products on landscape plants. Although greenhouse and nursery research, as well as

field experience, allows for general recommendations to be made, additional research

is necessary in this area of study.

2. Compost Application Methods

The method by which compost is applied is typically based on the compost’s

characteristics, how the compost is being used, the size of the project, and field

conditions. For small planting or mulching projects, compost may be obtained in

bags and spread by hand using a rake. For larger projects, compost may be obtained

in bulk, transported to the site in a dump truck or wheelbarrow and spread manually,

or by using tractor-drawn equipment. Where slopes are being mulched for decorative

purposes or erosion control, or compost is being applied to sites that are difficult to

access, blower type units have been used to propel the compost up to 60 m (200 ft).

Pneumatic blower trucks even exist which can apply product through a wide hose

(over 90 m [300 ft] in length) and apply material around plants and other objects.

A more common method to apply compost for various uses is with a manure spreader

or topdressing unit (Figure 7.1). A manure spreader uses rotating flails (paddles) to

project the compost into the air, whereas a topdressing unit uses a rotating, cylindrical

brush to project the compost down towards the soil surface. Both units may be

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Figure 7.1



Application of a thin layer of compost using a topdressing (brush type) spreader.



calibrated to apply lower rates (0.6 to 1.3 cm; 1/4 to 1/2 in. layer) or higher rates

(2.5 cm; 1 in. layer) of compost; however, the application of higher rates is slow

and may require more than one pass over the site. Side discharge manure spreaders

have been used to apply compost inside planting rows and tractor-trailers have been

fitted with flails to allow large volumes to be spread. Equipment has even been

developed to apply compost to a depth of 1.3 to 2.5 cm (1/2 to 1 in.) over a raised

nursery bed. Often, when rates of 2.5 cm (1 in.) or more are applied, piles of compost

are strategically placed throughout the site and a grading blade, York rake, or frontend loader/bulldozer blade is used to spread the compost. With experience and care,

accurate application rates are achievable (Alexander, 1996).

Continued innovations in compost application equipment will increase compost

usage. Thus, equipment is now available for purchase or rental to allow users to

more efficiently apply compost. Users should remember that the moisture content

and particle size of the compost will affect its spreadability. Standard “box spreaders”

and agricultural or commercial fertilizer/lime spreaders often have difficulty spreading coarse or wet compost (Alexander, 1996).

A guide to estimating the volume of compost required to cover a specific area

is given in Table 7.4.

B. Application Instructions for Specific Uses of Compost in the

Landscape

One of the most useful attributes which high-quality compost products possess

is their versatility. The ability to use compost products in a variety of end uses is

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Table 7.4 Compost Use Estimators

Cubic Meters (m3) of

Compost Required to

Cover 100m2



Cubic Yards (yd3) of Compost

Required to Cover 1,000 ft2

1/4-in. layer

1/2-in. layer

1-in. layer

11/2 in. layer

2-in. layer

21/2 in. layer

3-in. layer



⇒

⇒

⇒

⇒

⇒

⇒

⇒



0.75 yd3

1.5 yd3

3.0 yd3

4.5 yd3

6.0 yd3

7.5 yd3

9.0 yd3



0.7

1.4

2.7

4.1

5.5

6.8

8.2



cm

cm

cm

cm

cm

cm

cm



layer

layer

layer

layer

layer

layer

layer



⇒

⇒

⇒

⇒

⇒

⇒

⇒



0.6 m3

1.2 m3

2.5 m3

3.7 m3

4.9 m3

6.2 m3

7.4 m3



Adapted from Alexander, 1996.



one of the primary reasons why the use of compost in landscape applications, both

professional and non-professional, has grown so dramatically over the past 10 years.

However, to have success in the field, the proper compost products must be used

and the product itself must be used correctly.

Following is a detailed discussion of six common areas of compost use in

landscaping.

1. Garden Beds and Landscape Planters

Probably the most popular use for compost today is in garden bed establishment

and renovation. In this application, the product’s numerous attributes have allowed

for glowing successes from coast to coast. Two important factors that contribute to

the use of compost in planting beds are poor soil conditions on construction sites

once grading is completed, and the necessity of landscapers to be successful in their

planting endeavors, the first time. As a normal practice, builders will scrape soil

from a construction site in order to bring it to the correct grade. They will either

stockpile the soil, and reapply it later, or sell it to a topsoil dealer. Often, when it

is reapplied, the actual topsoil is mixed with subsoil, reducing its quality, or the

topsoil is buried under poor-quality soil when reapplied. In either case, the need to

improve soils around residential and commercial structures exists. When a homeowner or landscaper invests in landscaping a site, they expect that immediate and

positive results will occur, and persist. Therefore, using composts as a soil amendment to help ensure their success is seen as a good investment.

Application instructions — The compost application rate will vary depending

upon soil conditions, compost characteristics, and plant species to be established.

Compost has been successfully applied at a rate of approximately 1.7 cm (Maynard,

1998) to 7.5 cm (Beeson, 1995) (2/3-in. to a 3-in. layer), then incorporated to an

approximate depth of 15 to 20 cm (6 to 8 in.), resulting in an inclusion rate of 10

to 50% by volume. Performing a soil test will assist in determining proper compost

application rates. Typical application rates are between 2.5 to 5.0 cm (1- to 2-in.)

layer, 20 to 30% by volume (Smith and Treaster, 1991). Lower inclusion rates may

be necessary for salt-sensitive crops such as geraniums (Pelargonium sp.) or where

composts with higher salt levels are used. Once the compost inclusion rate is chosen,



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