"Panda" mulch

Could it reduce heat stress?

Last week I was visiting Hamilton on a hot sunny day, and happened to put my hand on the black plastic mulch covering the strawberry mound.  It was hot!

It made me wonder if we’re missing a trick with managing heat in field-grown strawberries. 

Black absorbs sun’s energy and heats up.  White, conversely, reflects the visible spectrum of light and heats up less. 

In the horticulture world, white-on-black plastic mulch (affectionately called “Panda” plastic) is laid with the white side up and the black side down.  The black provides weed control, while the white reflects light…and heat. 

A New England study using white plastic mulch for late spring lettuce (air temperatures ranging from 7-27°C) showed 1°C lower soil temperature under white than black plastic mulch.  A different study in Chile, this one in strawberries, showed that while the average soil temperature under the white plastic was 2°C lower than the black, the peak soil temperatures were 6°C lower.  The soil under the black plastic reached a blistering 42°C!  This was when the outside air temperature averaged 21.4°C and the maximum air temperature was 32°C. 

The cooler soil temperatures under the white plastic would be expected to result in slower plant growth in spring, so it would not be a good strategy for blocks of early varieties aiming for that high spring fruit price.  However, in blocks of day neutrals, and where longevity is more important than earliness, white-on-black plastic mulch could be a consideration.

If this idea is of interest to you, let’s chat!  We could organize to track soil temperatures on side-by-side beds of black and white mulch over the 2026 winter and spring, and find out the effect on fruit size and productivity during the heat of summer.  The colour of mulch could have some implications for thrips management, so a careful evaluation is important.

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