Subject: Re: mulches

From: [email-masked] (Edward Gilbert)
Date: 9 Mar 1995 18:23:02 GMT

I am not sure where this came from but I think it is Penn. State.
Article

Mulches

R. R. Rothenberger
Department of Horticulture, College of Agriculture

Mulches provide many benefits to plants. Benefits vary with the
material used, the type of soil, the kind of plant and the
cultural practices used.
     Mulches also may be used to make landscapes more attractive
and usable and to reduce the amount of maintenance work.
Why mulch?
     * Surface insulation 
          a. to conserve moisture 
          b. to modify extremes in temperature 
          c. to control weeds
     * Soil amendment 
          a. to improve soil aggregation and granulation 
          b. to increase water absorption and retention 
          c. to prevent soil compaction and improve aeration
     * Beautification 
          a. to make surface areas more attractive 
          b. to make surface areas more usable for paths, play
and sitting areas 
          c. to make areas easier to maintain

Types of mulch
Many types of material, organic and inorganic, may be used as
mulch. Organic mulches may break down in one season or less or
persist for more than one season. The first type is used
primarily in vegetable and flower gardens or around newly planted
trees and shrubs. They are usually decomposed enough by the end
of the growing season that they can be spaded or plowed under to
improve soil structure. Some common mulches of this type are
listed in Table 1.
     Organic mulches that persist for more than one growing
season are more useful around permanent plants. These are
summarized in Table 2.

A thick mulch provides excellent growing conditions for
rhododendrons as well as many other plants in the home landscape.
(photograph)

     Inorganic mulches may be gravel, crushed stone or some
manufactured product. Most of these materials are not so
beneficial to plants as the organic mulches. Some commonly used
inorganic mulches are summarized in Table 3.
     Though not generally considered mulches, some low-growing
ground cover plants produce many of the same benefits as mulch.
They shade the soil surface, keeping it cool in summer and at the
same time prevent evaporation. For more information on ground
covers, see Guide 6835, "Selected Ground Covers for Missouri."

Using mulches
On the whole, mulches should not be considered a fertilizer. Most
of them release some nutrients as they decompose, but the
fertilizer value is very small compared with the physical
effects. Where mulches are needed, use them for the mulch value
and add fertility as a supplement.
     The effectiveness of a mulch depends on the density and
texture of the material used and the depth of the layer applied.
A 4- to 6-inch layer of most products is needed to effectively
insulate the soil and prevent weed growth.
     In permanent locations a layer of black plastic film can be
used under the mulch to prevent weed growth and make the mulch
more effective. When black plastic is used, the mulch layer needs
to be only about half as thick as in areas without it. If areas
larger than 3 feet wide are covered with black plastic, holes
should be punched in it every 15-18 inches to allow good
distribution of water and air.

Mulching around ornamental plants makes mowing easier and reduces
chance of mower damage to plants. (photograph)

Table 1. Relative value of mulches that break down in one season
or less.

Mulching suggestions
Considering the growth requirements of the multitude of garden
and landscape plants, obviously there is no one mulch that will
be superior in all cases. The following general suggestions
should help in selecting the right mulch.

Bulbs. Among garden bulbs, lilies benefit more from mulching than
any other group. Two to 3 inches of wood shavings, straw, chopped
hay or other lightweight material serve to lower the summer soil
temperature, conserve moisture and give winter protection to the
more tender species.
     Most other bulbs are sufficiently winter hardy but benefit
from mulching for other reasons. Small, shallow-planted bulbs can
be heaved out of the soil by alternate freezing and thawing. This
can be largely prevented by light mulching. Mulches generally
improve the appearance of flowering bulbs growing in a bed of
otherwise barren soil. They offer a background for viewing the
new spring growth and also reduce the spattering of plants with
mud during rainstorms.

Table 2. Relative value of some persistent mulches.  

Evergreens. Plants that most need mulching are evergreen shrubs
and young evergreen trees, especially the broad-leaved types.
Mulches help prevent winter drying of these plants. Winter drying
causes foliage to become scorched and discolored over winter and
may cause the plant to die. Drying develops when foliage loses
moisture faster than it can be taken up by the roots from a dry
or frozen soil.
     Plants which should be mulched in practically every case are
azalea, boxwood, Chinese and Japanese hollies, Japanese andromeda
and rhododendron. Exotic evergreens and those planted north of
their best zone of adaptation should also be kept well mulched
the year around. 
     Coarse mulches should be used: wood chips, bark products,
shavings, chopped corn cobs, pine needles, hedge trimmings or
partially finished coarse compost. Mulches should be renewed in
early winter. A layer 2 to 4 inches deep is adequate in most
cases but can be more or less, depending upon site, soil,
climatic zone and the plant itself. The mulched area should be at
least as broad as the plant itself and preferably broader since
most woody plants have root systems which reach beyond the spread
of the branches.

Fruits. To keep young fruit trees growing well, maintain a
mulched area 3 to 4 feet in radius around the base. Coarse
materials such as hay, straw, wood or bark products are most
useful. The mulch should be removed and piled several feet from
the tree in early November to reduce the chances of mouse injury
in the tree roots. The mulch can be replaced in late March or
early April before new weed growth appears. Grapes and berry
bushes may be kept permanently mulched.
     Strawberries should be mulched preferably with clean straw
or with prairie hay about mid-December. Use enough mulch, loosely
scattered, to barely hide the foliage. In spring when new leaves
begin to grow, remove enough of the mulch to allow the plants to
emerge.

Table 3 Inorganic mulching materials. 

Mulching materials may be mounded up for winter protection of
roses.

Perennials. Most garden perennials benefit from summer mulches
for preserving soil moisture and for reducing soil temperature.
Some of those which most often need winter protection in Missouri
are baby's breath, bellflower, chrysanthemums, delphinium, hardy
gloxinia, hypericum, linum, lupine, oriental poppy, Stoke's
aster, thrift and thyme.
     Some perennials which are normally cold hardy are often
damaged by alternate freezing and thawing of the soil which may
loosen or heave the plants and expose them to drying. Among these
are aconite, coral bells and newly planted peony and plantain
lily.
     A few plants are extremely sensitive to damage by high
summer soil temperatures or drought. Delphinium, lupine, primrose
and Siberian iris are among the most troublesome in this respect.
     Two to 3 inches of straw, hay, wood shavings or partially
composted leaves would be an appropriate mulch for most
perennials. Pine needles or evergreen boughs are also effective.
When using a heavy layer of mulch on perennials, gradually remove
it during the onset of warmer weather in late winter. Heavy mulch
left too long may cause early emergence of weak, tender growth.
Such growth may be killed or permanently marked by freezing.

Roses. Experienced rose growers recognize the improvement in
vigor and appearance of roses as a result of summer mulching. The
mulch layer should be about 2 inches deep and of fairly coarse
material such as unfinished compost, aged sawdust, bark, milled
wood fiber or tobacco stems.
     By mid-November, provide adequate winter protection with a
mound of finished compost, garden soil or coarse peat. The mound
should be about 8 inches deep across the center of the plant.
Mounds should be removed in early spring when overnight
temperatures below about 28 degrees F are no longer expected. If
later, unseasonably cold weather threatens and new, tender shoots
have begun to grow, hasty covering may be needed.

Trees and shrubs. Trees and shrubs that gain most from mulching
are ones with shallow roots, ones which suffer from extended
drought or are otherwise damaged by high soil temperatures.
Flowering dogwood and sugar maple are examples of plants whose
leaves scorch easily in dry weather. Some leaves of birches,
willow and tulip trees often yellow and drop during extended
drought.
     All trees and shrubs should be mulched at planting time to
aid them in becoming established. A mulched area around the base
of trees and shrubs makes mowing easier and helps prevent mower
damage to the plant.
     The material used for mulching is perhaps less important
than the simple fact that the plants are mulched. Most coarse
materials are satisfactory. Avoid materials which form a tight
flake and those too unsightly in the landscape.

Vegetables and annual flower gardens. The primary reason for
mulching vegetable and flower gardens is to conserve soil
moisture. Crops most practical to mulch are beans, peppers, sweet
corn, tomatoes, vine crops and other long-term summer crops with
large amounts of foliage. Long-term crops started in the cool
season, including broccoli, cabbage, cauliflower and potatoes,
will also yield better when they are mulched. Asparagus and
rhubarb should be kept constantly mulched to conserve soil
moisture and reduce weed problems.
     Some of the best mulches for annual vegetable crops are
composts, straw, hay or other materials which will be largely
decomposed at the end of the season.
     Two to 3 inches of straw, hay, wood shavings or partially
composted leaves would be an appropriate mulch for most
perennials. Pine needles or evergreen boughs are also effective.
When using a heavy layer of mulch on perennials, gradually remove
it during the onset of warmer weather in late winter. Heavy mulch
left too long may cause early emergence of weak, tender growth.
Such growth may be killed or permanently marked by freezing.

-- 
Ed Gilbert
Tyrants have always some slight shade of virtue; they support the laws before destroying them.
--Voltaire