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Mulches - Alternatives To Peat And Their Use

Conference On Peat Alternatives Belfast March 21, 1991 Karen Foley 2016

Summary

Mulching has been practised for hundreds of years and a wide range of materials can be used as alternatives to peat. Bark chips and plastic film are two contrasting types of mulch that are increasing rapidly in importance at present.

Mulches can give excellent results when used in the right circumstances, but the outcome will be disappointing if conditions are unsuitable.

Growers should understand clearly what they want to achieve by using a mulch. They should also know the properties and cost of candidate materials so that a suitable choice of mulching material can be made.

INTRODUCTION

A mulch is any material applied to the soil surface to prevent loss of water by evaporation, to suppress weeds, to reduce temperature fluctuations or to promote productivity.

Although mulching is generally regarded as a good horticultural practice, undesirable side effects can also occur, so that mulches must be used sensibly. The value of mulching, like many other horticultural practices, depends very much on local circumstances, such as soil, climate and the type and growth stage of the plants to be mulched. As far as possible, clear specifications should be produced both with the regard to the mulching material and also the way it is used.

It is not surprising therefore that a paper on mulching must contain many qualifiers. For example a peat mulch can be particularly beneficial to rhododendrons and many other ericaceous species (Harig and Witt 1984), but is some circumstances it can be detrimental by absorbing and holding moisture and releasing it again to the air by evaporation. Mulching is an old horticultural practice used world wide and so a wide range of alternatives to peat, both organic and inorganic, are already in use.

Organic mulching material is bulky and costly to transport. Consequently organic mulches are unlikely to be economic unless material is available cheaply or as a local waste product (Rowe-Dutton 1957). Composted bark has become an important mulching material in the last decade but a wide range of other materials are also used. These include organic substances such as spent mushroom compost (Maher 1990), woodchips, pine needles (Paterson et al 1979), leaves, sawdust, straw, grass clippings and corn cobs (Gartner 1978); mineral material such as sand, gravel, stones and granite chippings (Wright 1985), rock wool (Paterson et al 1979) and manufactured materials such as plastic, paper, glasswool, metal foil, cellophane and urethane foam (Greager and Katchur 1975).

Proprietary mulches have also been developed e.g. strawdust consisting of resin impregnated granules of wheat straw. This material is long lasting, sterile and contains a slow release nitrogen fertiliser (Tuefel 1983).

Mulches are used in horticulture for a wide variety of purposes including regulation of soil temperature, light reflection and prevention of erosion, but moisture conservation and weed control are considered to be their most useful properties.

Soil moisture

By providing a protective barrier at the soil surface a mulch reduces water evaporation (Scholl and Schwemmer 1982). Suppression of weed growth also reduces moisture loss through transpiration. This enables the important surface soil layer to remain moister for a longer period than an unmulched soil surface.

Water penetration into the soil may be improved by certain mulches such as straw. This is due to a number of factors including the protection provided by the mulch against rain impact at the soil surface, reduced soil compaction (Ingle 1981), and probably to increased activity by soil fauna.

Where moisture conservation is a major consideration, organic mulches such as bark, straw or wood chips will be preferable to plastic as they tend to retain higher moisture levels (Ashworth and Harrison 1983). However there are large differences between organic mulches in their moisture conservation properties, straw being more effective than manure with hay and wood shavings intermediate (Harris and Yao 1923). The moisture holding properties of any individual material is affected by its physical condition. Finely ground bark with particle sizes up to 25 mm, retains more moisture than coarsely ground bark (75 mm) with a medium grind (50 mm) intermediate (Gartner 1978).

Plastic and other solid synthetic mulches may prevent water penetration and cannot be laid over large areas without some means of enabling water to reach the soil, such as perforating the film. In addition the high temperatures that develop under clear plastic will also tend to reduce soil moisture levels (Ashworth and Harrison 1983).

Higher soil moisture does not always benefit plant growth. On low lying, poorly drained sites or on soils that do not dry out quickly, excessive moisture under mulches during wet springs, may result in root asphyxiation (Agulhon 1975). Impeded drainage and nitrogen deficiency were suggested as the likely causes of the better response of the moisture-loving alder than sycamore and lime to mulches of bark, sewage sludge and press board sheets (Insley 1981).

Weed control

There are many reports of successful weed control with a wide variety of mulching materials. Good results have been achieved with many different kinds of organic material. The depth or thickness of a mulch necessary to control weeds will depend on the type of material used. A depth of about 100 mm when settled is required for straw (Bushnell and Weaver 1930) and about 50 - 75 mm for sawdust (Rowe-Dutton 1976). A deep mulch (100 mm) of hardwood bark chips, sawdust or crushed corn cobs gave more effective control than a shallow mulch (50 mm) of the same materials. Provided a 75 mm layer of bark mulch is properly applied, 95% weed control should be achieved over a three year period (Campbell-Lloyd 1986).

Apart from the smothering effect of mulches, chemicals in the materials used can also affect weeds. Phenols and tannins in coniferous bark and sawdust improved the degree of weed control and reduced cultivation costs compared with chopped bark and straw and a mixture of chopped shrub waste and limestone gravel (Kolb et al 1985). Similarly better weed control was obtained in roses with sawdust than with rockwool (Paterson et al 1979). Although organic mulches can be effective against annual weeds they usually have little effect on established perennials.

Perennial weeds can emerge through deep layers of organic mulch and, if present when the mulch is applied are likely to thrive because of the absence of competition from annual weeds. Opaque plastic materials give excellent control of annual weeds and are more effective than organic mulches against perennials. However, some of the more aggressive perennial species, or those with sharply pointed shoots such as scutch grass (Elymus repens) can penetrate thin polythene (38 micron) film (Davison 1983).

Despite the general efficacy of mulches against weeds, problems can arise with both opaque synthetic and organic mulches. If plastic mulches are torn, accidentally or to assist water penetration, weed growth through the holes will be vigorous (Rowe-Dutton 1976). Even with undamaged plastic vigorous weed growth can occur at the gap around the stem or stake.

Although transparent plastic film results in higher soil temperature than opaque film and crop growth may be enhanced initially (Agulhon 1975), the vigorous weed growth that occurs beneath clear plastic is a severe limitation. Consequently transparent films are little used for mulching of perennial plants. Some organic mulches (bark and sewage sludge) can break down quickly and be reinvaded by weeds (Insley 1981). Finely pulverised grades of bark, in particular, tend to be colonised rapidly (Campbell-Lloyd 1986). Moreover, the weed problem may be increased by weed seeds introduced in certain mulches, such as fresh manure or hay cut when seeding.

Soil temperature

Each mulch type creates its own unique soil temperature regime and big differences have been recorded between organic and plastic mulches. Under organic mulches soil temperatures are lower during the day and slightly higher at night than those in bare soil (Paterson et al 1979). Temperature fluctuations are therefore reduced (Ashworth and Harrison 1983) but organic mulches have less effect on seasonal temperature variation (Bredell and Barnard 1974).

The effect on soil temperature will depend on the depth and thickness of the mulch material. A deep mulch (100 mm) of hardwood chips, sawdust, jointer curls or corn cobs had a better insulation value than a shallow mulch (50mm) (Gartner 1978).

Dark coloured mulches such as black polythene, absorb the sun's rays and may increase soil temperature considerably especially during sunny periods. In a trial in Wisconsin , plastic mulches resulted in significantly increased soil temperatures at 100 mm depth compared with organic mulches (Ashworth and Harrison 1987). Higher soil temperatures were also recorded under black plastic than under bark or hay and the differences were greatest early in the season (Litzow and Pellet 1983). Plastic mulches reduced the degree of diurnal variation in France by raising soil minimum temperatures (Agulhon 1975).

Effect of mulches on soil nutrients and physical properties

Different mulches will affect soil fertility and structure in a variety of ways. In a comparison of nine mulches, including straw and synthetic materials, the soil under bark showed the highest pH, organic matter content and potassium levels (Ashworth and Harrison 1983). Bark mulch also gave a greater increase in potassium, calcium and magnesium than sawdust or corn cobs (Gartner 1978). Spent mushroom compost is a rich source of nutrients, an application of 20 tonnes per acre will provide 36 kg nitrogen, 34 kg phosphorus and 158 kg potassium per acre (Maher 1990).

The application of mulching materials with a high carbon/nitrogen ratio (> 30:1) will result in a depression of nitrification at least initially. Mulches such as fresh sawdust (C:N ratio 500:1) and wheat and barley straw (100:1), normally will require additional applications of nitrogen to compensate for this imbalance, but mulches of young grass clippings (12:1), average grass clippings (19:1) or seaweed (19:1) will not (Wright 1982a).

Plants of Spiraea japonica mulched with conifer sawdust were smaller in size than unmulched plants after six years, but growth of both unmulched and mulched plants was greatly improved with applications of ammonium sulphate (Kolb 1984, Karbe 1984). The growth of rhododendrons was temporarily improved by a mulch of fermented bark while their growth was adversely affected by unfermented bark throughout a three year study period (Harig and Witt 1984). Better growth of trees and shrubs was recorded with a combination of bark mulch plus nitrogen fertiliser than with fertiliser or mulch alone (Whitcomb 1978).

Apart from the effect of mulching material on nitrification, plant growth may also be affected positively or negatively by chemicals in the mulching material. The growth of seedlings of Sitka spruce and Lodgepole pine was improved by the nutrients washed out of a mulch of bracken fern applied to nutrient deficient acid heath soil and removed before the tree seeds were sown (Holmes and Faulkner 1953).

Plant growth and crop yield

In view of the complex effect of mulches on many different soil functions, it is not surprising that many different types of mulch affect plant species in different ways and that no single type of mulch performs best in all situations or for all species (Ashworth and Harrison 1983). Good response in terms of increased plant vigour has been obtained with a wide variety of different plant materials including pine bark (Insley 1981), hay, black plastic, calcined clay (Litzow and Pellet 1983), heavy duty green plastic (Ashworth and Harrison 1983), bark and sawdust (Kolb et al 1983), and plastic and gravel mulch (Werken 1981).

Mulches of black plastic (38 or 125 microns thick) have given consistently good results on woody ornamentals and fruit plants without adverse effect on any plant species (Davison 1982). Average increase in the growth of apples and blackcurrants mulched with black polythene was in the order of 30 - 40% compared with only 10% for a straw mulch. In these trials polythene-mulched crops made more growth than those kept weed-free with herbicides or with hand weeding. However, Whitham (1982) obtained a strong correlation between growth of Eucalyptus and weed control with most mulching and herbicide treatments ested. In this work, mixtures of simazine and aminotriazole gave greater growth than pine bark, grass hay, sawdust, black plastic, scoria, newspaper and hoeing. [*]

The increased vigour of plants mulched with opaque plastic compared with unmulched plants may continue for several years. The weights of shoots on mulched vines were much higher over a five year period than those from non-mulched vines (Agulhon 1975).

In Britain, a mulch or a combination of mulch plus herbicides often gives higher yields of apples, blackcurrants, raspberries and nursery stock than the use of herbicides alone (e.g. Davison and Baily 1980). However, in Ireland there has been a general tendency for fruit crops on herbicide-treated, unmulched plots to outyield mulched ones (Robinson and O'Kennedy 1978).

In some cases the reduction of yield on mulched plots has been attributed to lower air temperatures and increased frost injury (Robinson 1966), but the effect of an organic mulch in reducing soil temperatures during the growing season or in maintaining excessively moist conditions in the soil may also be responsible.

More extensive root systems have been recorded under mulches (Agulhon 1975, Allmaras and Nelson 1971). The total weight of a vine root system in the 0 to 0.60 m soil layer for a mulched plant was 150% higher than for a non-mulched, cultivated plant after one year. Initially plastic film tends to encourage shallow rooting, 92% of the roots of a mulched vine rootstock occurring in the 0 - 30m layer and none in the 0.45 and 0.60 m layer, compared with only 19% of the roots of the cultivated vines in the 0 - 0.30 m layer. The absence of exploitation of the deeper soil layers by mulched plants is normally shortlived.

Further studies with vines in France showed that after three years, the depth of the root system was similar both for mulched and cultivated plants, but that the superiority of mulched plants was due to their more vigorous root growth in the 0 - 0.15 m layer (Agulhon 1975).

Not only do plants respond differently to different mulches but different plant species may respond differently to the same

mulch. Mulching with bark or sawdust significantly increased the growth of Hypericum, Potentilla and Cotoneaster but not of Spiraea, Arundinaria or Geranium (Kolb et al 1985).

Plant establishment

The rapid development of an extensive shallow root system on vines mulched with plastic enabled plants to recover more rapidly after planting (Agulhon 1975). This was attributed to the greater development of surface roots and the better balanced root system of young plants. The establishment of ornamental perennials and shrubs was also improved by organic mulching materials especially bark and sawdust (Kolb et al 1983).

Appearance of mulches

The appearance of a mulch is more important in landscape situations than in field grown food crops or nursery stock. Bark, both chips from softwood and coarse ground and screened hardwood, make decorative mulches (Gartner 1978). Of nine different mulches tested in Wisconsin , bark was considered to be the most satisfactory since it blended with the surrounding soil (Ashworth and Harrison 1983). In this trial, clear polythene, which became muddy and trapped weed growth underneath, and other synthetic mulches which tore, were particularly unsightly.

In prestige situations where cost is not a limiting factor, the moisture-conserving and weed-suppressing advantage of plastic may be combined with the pleasant appearance of natural mulches by covering the plastic mulch with a thin layer of bark or granite chips (Wright 1982a).

Economics

The use of mulches can greatly reduce the labour required for weed control. In Britain , a hand hoeing/forking bare soil regime between shrubs and trees required about 33 man hours per 100 sq m per year compared with 5 man hours for a mulch layer (Wright 1982a). In Germany , cultivation costs were reduced on average by 23% to 40% with bark and sawdust mulches, by 10 to 22% by straw and by 5 to 8% by chopped shrub waste and limestone gravel compared with unmulched controls (Kolb et al 1985). Reducing the thickness of the mulch from 30 mm to 19 mm reduced the cost of the mulching treatment but reduced its effectiveness.

Organic mulches would be used much more widely for weed control if they were not so expensive. Wright (1982b) calculated that the costs per sq m for a 50 mm thick mulch were peat 1 - 1.20, bark 0.6 - 0.7 and coarse gravel 0.9 - 1. The price of black plastic (150 gauge) for a 1 sq m mulch around trees was 0.2 - 0.3 per tree.

The economics of mulching does not depend only on the initial cost but also on the longevity of the material used. Newspaper and a thin mulch of straw had virtually disappeared after six months, but chopped bark, sawdust and black polythene lasted well and were not substantially different after six months (Ingle 1981).

The transport of bulky organic mulches adds considerably to their costs (Insley 1981). About 500 cu. m of mulching material is required per hectare to give a minimum mulch depth of 50 mm. Heavy duty plastic can be handled more easily, but light synthetic mulches are often difficult to lay even in a light wind (Ashworth and Harrison 1983).

Despite the high price of many organic materials, the cost of mulching was recouped in one year in Germany due to reduced maintenance cost and improved plant establishment (Kolb et al 1983). However a comparison of weed control methods in Sweden showed that chemical weed control was least expensive, followed by a combination of chemical treatments and mulching and by mulching alone (Christensson 1982).

Plastic film

New technology has resulted in the increased availability of a wide range of plastic film for mulching (Gilby 1990a). It is now possible to formulate plastics to control or utilise more effectively the heat and light energy from the sun and also the heat energy radiated from the soil. When white coloured plastic is used, more visible light is reflected back towards the crop by the film to aid photosynthesis. On the other hand, care is needed with dark coloured plastic where the surface temperature of the mulch may rise excessively under hot conditions and cause crop injury.

Among the wide range of monolayer mulching films currently available are clear, black, white, black/white and thermic brown and blue films. The properties of these films in comparison with uncovered soil is shown in Table 1 (Gilby 1990b).

Table 1. Properties of monolayer plastic mulches compared with bare soil

Film type  Herbicidal  Soil heating or cooling(-) Heat retention  Film temp Light reflection
Clear - - - + + + + o o
Black + + + + + + + + + + - - -
White + - + - - + + +
Black/White + + + - - - + + + + + + +
Thermic Brown + + + + + + + o - -
Thermic Blue + + + + + + + + + (blue)

+ = greater, o = similar, - = less

Clear polyethylene film (15-50 micron) is used to warm up soil in early spring and enhance seed germination. This practice is most popular in Mediterranean countries, but is gaining popularity in Britain and Ireland now that the process of laying plastic has been completely mechanised. Further improvements are expected in combining mechanical laying of plastic mulch with other operations such as seeding, planting and the placing of irrigation pipes (Castillo Prados 1987).

In contrast to temperate and Mediterranean countries, where clear film is used to increase soil temperatures, black/white film with the white side uppermost is useful in tropical countries to mitigate the effects of high soil temperatures. At the same time weed growth would be suppressed and the exposed surface of the white film would remain relatively cool.

Experiments are in progress in Britain with blue 'thermic' mulching film. This reflects photosynthetically active light at the blue end of the spectrum which is believed to be beneficial for strawberries (Gilby 1990b).

Coextruded combinations of black with white or silver are now available. These have similar energy transmission properties to black films except that the soil temperature tends to be even lower (Gilby 1990a). The reflection of both light and heat results in the film remaining cool, but the plants benefit from additional reflected light. This film can be used to delay the ripening of late-season strawberry varieties to further extend the season.

In addition, coextrusion makes possible the design of multilayer films in which different polymers, pigments or different additives with different wavelength absorption and transmission properties can be incorporated into the various layers (Gilby 1990a). It is possible in this way to be selective about the wavelengths that are either transmitted, absorbed or reflected by the film. The ability to design a mulch to reflect light of any colour is of potential importance in view of the varying response of crops to different wavelengths.

Specifications

In the past organic mulches had to be inexpensive because they were bulky to transport and were often sold without precise specification. Now that there is a growing market for more expensive bark mulches and plastic film with very different properties, more detailed specification is needed. For example, a range of different bark types is available to suppress weeds for several years and improve the appearance of prestige and other situations.

Exact specification is necessary both with regard to how the material should be laid and also to the grade of bark to be used. For example, the ground should be levelled off to a tolerance of 20 mm to remove clods, and edges between the area for mulching and lawn or paving should be profiled down to 75 mm so that mulch depths on all edges are no less than 75 mm (Campbell-Lloyd 1986).

Many different grades of bark are now available depending on source of bark, composting period, degree of grading and wood content. For example one firm is currently selling at least nine grades of bark for mulching, ranging in particle size from 0 - 5 mm for annual plantings up to 45 - 80 mm for large shrubs and trees.

With certain organic mulches, information on the nitrogen content is required as compensatory applications of nitrogenous fertiliser are normally needed if the carbon/nitrogen ratio is above 30:1 (Wright 1982a).

Discussion

Mulches can give excellent results when used in the right circumstances, but the outcome will be disappointing if conditions are unsuitable. With the growing emphasis on reducing the use of pesticides, mulches provide a useful non-chemical means of weed control. Because of their attractive appearance, bark chips are useful for ornamental plantings but plastic is more practical where aesthetics are not of great importance.

The benefits of a mulch are, however, usually much greater than weed control alone.

The improved plant growth and vigour often recorded may be due to the conservation of soil moisture by reduced evaporation and run-off, increased photosynthesis, the provision of a more favourable soil temperature regime, improved water infiltration, increased availability of mineral nutrients, enhanced nitrification, additional nutrients and organic matter derived from a decomposing mulch, or the preservation or improvement of soil structure. In addition, mulches may increase the density and spread of roots by increasing the moisture content of the surface soil.

Where mulches result in decreased plant performance, this effect too may be due to a variety of factors, including reduced nitrification, retention of excessive soil moisture, or the reduction of soil temperatures below optimum for heat-loving plants.

Mulches are used in so many different situations and can affect so many different interacting soil factors that it is not usually possible to identify only one factor as being the main reason for good or bad results.

Literature Cited

  • Agulhon, R. 1975. The mulching of vines. Plasticulture 25 supplement au numero 155 (Mars 1975) de la revue 'P.H.M.- revue Horticole' p 1-16

  • Allmaras, R.R. and Nelson W.W. 1971. Zea mais root configuration as influenced by some inter-row variants of tillage and straw mulch management. Soil Sci. Soc. Amer. Proc. 35:974-980.

  • Ashworth, S. and Harrison H. 1983. Evaluation of mulches for use in the home garden. HortScience 18:180-182.

  • Bushnell, J. and Weaver, W.E. 1930. Straw mulch for early potatoes. Ohio Agric. Expt. Sta. Bimonthly Bul. 143:33-37.

  • Campbell-Lloyd, R. 1986. Mulching - doing it right. Landscape Design 163:75.

  • Castillo Prados, N. 1987. Plasticulture in southern Europe . Driving forces and material requirements. Proc. ECMRA Conf.1987.

  • Christensson, H. 1982. Costs of weed control in ornamental beds in parks. Proc. 23rd Swedish Weed Conf. Uppsala , Sweden 1:58-67.

  • Creagur, R.A. and Katchur, D. 1975. An evaluation of plastic and fibrous materials as mulches for total vegetation control. HortScience 10:482.

  • Davison, J.G. 1982. Black plastic benefits young fruit trees and bushes. Plasticulture 193:35-40.

  • Davison, J.G. 1983. Weed control in newly planted amenity trees. Proc. Symp. on Tree Establishment. Univ. of Bath , 14-15 July 1983 p.59-67.

  • Davison J.G. and Baily, J.A. 1980. The effect of weeds on a range of nursery stock species planted as liners and grown for two seasons. Proc. Weed Control For. Conf. p.13-20.

  • Gartner, J.B. 1978. Using bark and wood chips as a mulch for shrubs and evergreens. Amer Nurseryman 147(10):9, 53-55.

  • Gilby, G.W. 1990a. Speciality horticultural films, based on polyethylenes, for greater control of the growing environment. Proc. X1 International Congress on 'The use of plastics in agriculture'. New Delhi , India . G 67-G 73.

  • Gilby, G.W. 1990b. Personal communication.

  • Harig, R. and Witt, W.W. 1984. Einfluss von Mulchmaterialien/ Substraten auf den Zuwachs von Rhododendron-Hybriden und den Unkrautbewuchs. Zeitschr. fur Vegetationstechnik im Landschafts und Sportstattenbau. 7(3)110-114.

  • Harris, F.A. and Yao , H.H. 1923. Effectiveness of mulches in preserving soil moisture. J. Agr. Res. 23:727-742.

  • Holmes, G.D. and Faulkner R. 1953. Experimental work in nurseries. For. Comm. Rept. For. Res. 1952, 15-28.

  • Ingle, A. 1983. Comparison of mulches in their effects on weed germination, soil nutrient status, soil physical conditions and worm population. Hort. Re. Centre, Levin. Final Rpt Expt No. 46/07.

  • Insley, H. 1981. Roadside and open space trees. Research for practical arboriculture. Seminar Proc. For. Comm. Occasional Paper 10:84-92.

  • Karbe, W. 1984. Mulchstoffe in Pfanzflachen Auswirkung von Pflegemassnahmen. Gartenamt 33(9):617-621.

  • Kolb, W. 1983. Auswirkung von Bodenentseuchung und Mulch auf die Fertigstellungspflege von Pflazenflachen. Gartenamt 32(6)374-376.

  • Kolb, W. 1984. Wirksamkeit der Stickstoffdungungen auf die Kompostierung von Mulchstoffen in Pflanzflachen. Rasen Grundflachen Begrunungen 15(10):1-14.

  • Kolb, W., Schwarz, T. und Trunk, R. 1983. Kostens und Wirkungsvergleich bei die Verwendung verschiedene Mulchstoffe zu Pflanzungen im Rahmen der Bodenpflege. Zeitschrift fur Vegetationstechnik im Landschafts- und Sportstattenbau 6(2): 65-72.

  • Kolb, W., Schwarz, T. und Trunk, R. 1985. Auswirkung von Mulchabdenkungen auf Anwachsergebnis, Pflegekosten und Wachstum von niedringen Stauden und Geholzen. Rasen Grundflachen Begrunungen 16(4):120-126.

  • Litzow, M. und Pellet, H. 1983. Influence of mulch on growth of green ash. J. Arboricult. 9(1):7-11.

  • Maher, M. 1990. The value of spent mushroom compost as an organic manure. Proceedings 8th National Mushroom Conference. Teagasc, Dublin . 29 - 34.

  • Paterson , D.R., Fugus, M.C., Earhart, D.R. and Walker , D. W. 1979. Mulching effects on soil temperatures, weed control, growth and survival of rose varieties. Progress Rpt. Texas Agr. Expt. Sta. PR-3558.

  • Robinson, D.W. and O'Kennedy, N.D. 1978. The effect of overall herbicide systems of soil management on the growth and yield of apple trees. Scientia Horticulturae. 9:127 - 136.

  • Rowe-Dutton, P. 1957. The mulching of vegetables. Commonwealth Bureau of Hort. and Plantation Crops. Tech. Commun. 24.

  • Rowe-Dutton, P. 1976. Mulching is important. The Garden. J. Royal Hort. Soc. 101:135- 139.

  • Scholl, W. and Schwemmer, E. 1982. Verwendung und Untersuchung von Baumrinden und Rinden Produkten. Deutscher Gartenbau 36(8):330-334.

  • Tuefel, D. 1083. Strawdust - an alternative growing medium. Combined Proc. Intl. Plant Propagators' Soc. 33:71-72.

  • Werken, H. van de. 1981. Fertilisation and other factors enhancing the growth rate of shade trees. J. Arboricult. 7(2):33-37.

  • Whitcomb, C.E. 1978. Effects of black plastic and mulching on growth and survival of landscape plants. Oklahoma State Univ

  • Agric. Expt. Sta. Res. Rep. P-777, p.13.

  • Whitham, A.E. 1982. The effects of some methods of weed control on the growth of young plants. Australian Parks and Recreation. August 82, p.41-46.

  • Wright, T. 1982a. Large gardens and parks. Maintenance, management and design. Granada , London . pp 194.

  • Wright, T. 1982b. Mulches and weed control. Landscape Design 140:27-29.

  • Wright, T. 1985. Labour saving in the garden by design. The Garden. J. Royal Hort. Soc. 110(5):225-233.

Further Reading

  • Jacks, G.V., Brind, W.D. and Smith R. 1955. Mulching. Commonwealth Bureau Soil Sci. Tech. Commun. 49.

  • Rowe-Dutton, P. 1957. The mulching of vegetables. Commonwealth Bureau of Hort. and Plantation Crops. Tech. Commun. 24.

  • Rowe-Dutton, P. 1976. Mulching is important. The Garden. J. Royal Hort. Soc. 101:135- 139.

[* Footnote. Since this article was written, the herbicide, simazine, has been banned in Europe under Commission Decisions 2004/141/EC(3), 2004/248/EC(4), 2004/140/EC(5) and 2004/247/EC(6), taken within the framework of Council Directive 91/414/EEC of 15 July 1991. This came into effect on 26th April 2004.]

 

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