Using Plastic Mulch to Suppress Weeds in a Cannabis Field

Professor DeBacco


Plastic Mulch Benefits
Long used option worldwide since the 1960’s mainly with annual plants.
Goal is to provide
Weed control
Improved plant growth
Modify soil temperature
Retain soil moisture
Increase yields

Plastic Mulch in Cannabis Production
Good option if starting with clones due to their poor ability for cannabis to initially complete with weed species.
Also, the use of clones does not allow for the use of post emergent herbicides.
In addition plastic mulch can increase the soil temperature allowing for early plants to establish quicker.

Plastic Mulch Challenges
Mulch removal and disposal can be labor intensive and expensive
Cost
Estimated to cost up to $534/ha in horticultural systems with a 2.4-m spacing between bed centers (Velandia et al., 2019).
Disposal
PE mulch also has waste management challenges (Kasirajan and Ngouajio, 2012).



Recycling Plastic Mulch?
About 90% of used plastic mulch used in the United States mostly ends up in a landfill, stockpiled or burned.
It is often not recycled due to limited sites and contamination during usage and the high cost of transport
(Grossman, 2019; Levitan and Barros, 2019).



Before Installation…
Growers should be committed to a drip irrigation method with a fertilizer injector.
Since the soil will be “sealed” under plastic irrigation will very likely be needed.
In addition, side dressing with nutrients is also impeded with plastic mulch so having a fertigation system is advised.
However, soil should still be amended (if needed based on a soil test) before mulch is applied to the soil.



Plastic Mulch Options
Width (how wide will your rows be?)
Common widths are 36 inches to 60 inches, but other options may be available
Texture (slick or embossed)
Embossed plastic has visible patterns on the surface and is more resistant to damage due to punctures, wind fatigue and cracking than non-embossed mulches.
Linear low density, has a slick surface appearance, but may have a line pattern with the goal to reduce the chance of tears occurring while in use.
Thickness
Thickness varies from 0.6 mil to 2 mil or greater.
Be sure to use an adequate strength material. A 1 mil to 1.25 mil embossed plastic is adequate for most applications and is recommended despite potential increase in cost.



Plastic Mulch Color Choices
Most common color option is the traditional black
However, some growers are option for white and white on black, which may be used with either side facing upward, depending on the specific need.
Clear mulch is great for warming the soil, but has limited weed suppression abilities.
Aluminum (or silver NOT gray) reflective mulch reflects solar radiation and research has shown it can repel aphids which can spread viruses.
It can also have a cooling effect on the soil.
Other colors of mulch may affect plant growth in positive ways but more research needs to be done in regards to cannabis.



Plastic Mulch Equipment
Field Prep
Mulch layer (with drip irrigation wheel)

Mulch lifter




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