Growing Hemp on a Green Roof? Is it Possible?

Growing Tomatoes on a green roof is similar in many ways to growing hemp on a green roof.

It is probable that hemp planted green roofs will become a norm in the future.

Hemp is a viable green roof crop with many positive economic and ecological attributes.  For instance hemp is a choice raw material in the making of paper and rope.

But what are the challenges of growing hemp on a rooftop?  There are many.  However, I believe that as in any green roof plant, hemp can be grown across a green roof system with proper consideration given to those challenges.

First, one must be familiar with the hemp plant and its growing requirements.  There are many varieties and cultivars of the hemp plant and each will have its own historically preferred conditions.  So knowing your hemp plant is important.

In addition to understanding hemp's growing requirements you must have a solid knowledge of organic hemp pest control.  I believe all rooftop grown hemp must be treated for pests using only organic integrated pest management (OIPM) principles.

Integrated, organic pest management with an emphasis on cleanliness and exclusion should be the management approach of all green roof operations, hemp or otherwise.  Green roofs are subject to constant winds.  Spraying chemical herbicides and pesticides on a rooftop could potentially expose adjacent neighbors to wind carried toxic compounds.

Irrigation is another issue to be resolved for hemp plants grown on green roofs.  Hemp, as all members of the Cannabaceae, are C3 plants.  C3 plants have evolved photosynthetic systems that are prone to support fast growth but also rapid desiccation potential.  Hemp must not be overwatered yet the plant also requires consistent water supply to its roots.

Before deciding on the best irrigation system for a hemp planted green roof there are other factors to be considered, including; heat tolerance, light levels, flowering requirements and more.  Some of hemp's optimal growing requirements can be addressed with either added mechanical systems or also with plant portability.

Temperatures on a rooftop can reach upwards of 150 degrees F or 66 degrees C.  Hemp won't survive long under those temperatures without a level of temperature mitigation.  Temperature mitigation options can include shade systems such as movable polypropylene screens or planting location strategies which take advantage of existing shade.

Other temperature options can include the possibility of utilizing a portable growing system that can be moved across the rooftop or off the rooftop as necessary.

Of course as with any mechanical system the rule should be; "the simpler the better ".  All mechanical systems can fail.  

Sunlight exposure and shading also have to be factored into flowering requirements.

Green roof winds can also be a serious challenge to fast growing and in some cases tall hemp plants.  Storms can quickly develop and hail or high speed winds may break, damage or topple hemp plants.

Despite all the challenges and considerations a rooftop grower of hemp must take into account, there are potential advantages to green roof hemp cultivation.

Free sunlight, rain, constant breezes and a measurable reduction of vectored pests may be benefits of rooftop hemp farming.

We will look at the many disadvantages and positive aspects of growing hemp on rooftops in future posts.

In the meanwhile, consider the issues associated with growing hemp on a green roof.  Talk with experienced green roof designers and growers.  As hemp becomes more excepted the popularity of hemp green roofs will only increase.