Mulching with Plastic

WARNING – As there is ongoing research about plastic in soil this page is retained for reference and is not here as a recommendation. We do not use plastic for mulching as we do not want micro-plastic particles in our soil.  We make our own mulches from composted garden waste (Updated 19/04/2020)

Elizabeth Parker

Over the past few years much work has been done world-wide in the horticultural industry on mulching with various different types of plastic. In Mexico during 1992 /93 research was undertaken to determine the effects of temperature and soil moisture under three different plastic mulches and it’s effects on the growth and yields of cucumbers.

It was found that cucumbers grown under all the types of plastic flowered earlier and cropped sooner with an increased yield compared to the unmulched plants. Marketable yields in T/Ha were:

Clear – 63.3,  White – 46.2,  Black – 44.8,  Unmulched – 2 1.6

All mulches significantly increased soil moisture compared with the unmulched bed.

While the soil temperatures were increased by all the plastics the midday soil temperature at a depth of 10cm were highest beneath the clear mulch.

Corroboration of the effects of soil solarization comes from Brazil. Here inside a plastic greenhouse soil  temperatures at 2cm and Sam depth showed an increase of 10C compared with the bare soil outside the greenhouse. At depths of up to 10cm temperatures exceeded 50C or more on several days during 1994/95. At these temperatures plastic mulches might be used as a means of soil disinfectation.

Plastic mulches were used on other research in Malaysia to observe the effects of different mulches on the pests and diseases of peppers. There it was found that white and silvery plastic mulches reduced thripes and delayed virus epidemics.

Over here in Eurpoe the Italians have been using polythene mulch to promote early growth of walnut trees (Juglans regia and the French hybrid NG23xRA). They found the use of polythene mulch promoted stem height and diameter growth.

In Japan reflective film mulching has been used on carnations when the cut f lower yield during the first three months of the harvest period increased from 33% – 107% in comparison with the unmulehed plot. Total yield of cut flowers was increased by 1 5A. It was felt this was because the reflective film had lowered the soil temperature and reflected solar radiation to the low and middle leaves.

Researchers in the USA have been different coloured polythene mulches and have concluded that the coloured ones work better than black. Cucumbers with a red mulch gave an increased yield of 18%, peppers with a silver mulch gave an increase of 22%, squashes with blue or red polythene gave 14% more, however, tomatoes preferred brown and gave 15% more. These coloured mulches usually gave larger vegetables which ripened more quickly. But
beware of yellow polythene as it attracted insect pests.

It might be an idea  to try experiments with different colours and types of plastic mulch on plants in their gardens during the coming season. Have a go and let us know how you get on.

1. “Soil temperature and moisture under different plastic mulches and their relation to growth and cucumber yield in a tropical region.” Fariaslarious J. Orozco M. Guzman S. Aguilar S. Gartenbauwissenscaft 1994 Vol 59 No.6 pp.249-252.

2 “Soil by solarization inside a plastic greenhouse in Santa-Maria, Brazil.” Streck N. A. Schneider F. M. Buriol G. A. Agricultural and Forest Meteorology 1996 Vol 82 No. 1-4

3. “Integrated crop management of hot peppers (capsicum spp) under tropical lowland conditions.” Cos J. G. M. Uhan T. S. Sutarya R. Crop Protection 1995 Vol 14 No.6 pp.445-452

4. “Influence of alfalfa intercropping and polythne mulching on early growth of walnut in Italy.” Pans P. Cannata F. Olimore G. Agroforestry Systems 1995 Vol 31 No.2 pp.169-180

5. “Effect of combination of reflective film mulching and shading on the growth of carnations”. Yamaguchi T. Ito A. Koshioka M. Jarq – Japan Agricultural Research Quarterly 1996 Vol 30 No.3 pp.181-188

6. “The Garden.” Royal Horticultural Society, Dec 1996, Vol 121 part 12 p752

(Reproduced with the permission of B O G Birmingham Organic Gardeners)