Happy Urban Dirt

Is your yard uneven or sloped but you want to build a greenhouse? This may not seem like the “ideal spot,” but building a greenhouse on a slope actually has several benefits that you won’t get by placing it on level ground.

Below is an excerpt from Biointegrated Farm by Shawn Jadrnicek and Stephanie Jadrnicek. It has been adapted for apply on the Internet.

(Photos courtesy of Shawn Jardnick unless otherwise noted.)

Building a greenhouse on a slope: leaving the level ground

When I started building greenhouses, I always followed the standard recommendations for the correct location of the house: choose a level place and carefully level the area so that the water drains and moves away from the greenhouse. Eventually, the water flowing back into the greenhouse creates a swampy mess. If water flows through the greenhouse, it removes valuable heat as it passes from the inside to the outside.

This is the skeleton of the first greenhouse I built on a sloping site – in a steep garden on my father’s property. The greenhouse slopes in two directions: 8 percent from back to front and 2 percent from right to left. Water flows from the highest corner (top right corner of the greenhouse) to the lowest corner (bottom left corner). Terraces outside the greenhouse and raised beds inside, placed in contours, snail-paced water flow and allow water infiltration.

My clear thoughts changed when my father asked me to build a greenhouse for him. I agreed to this venture, choosing the perfect spot for the greenhouse near his house. It was close enough to the house to easily run electricity and sewage.

Using the angle finder, I checked to make sure distant trees wouldn’t shade the greenhouse in the middle of winter, when it needed the sun the most. After making sure I had chosen the perfect spot, I happily announced the results of my site analysis to my father.

Design considerations when creating a greenhouse on a slope

However, like many design problems, the sweet spot presented me with a perplexing problem that forced me to change my perspective on the “right way” of doing things.

Sometimes bureaucratic red tape forces you to change your mind, such as a required setback at the edge of your property. Safety may also be an issue – for example, an overhead power line.

Whatever problem arises, solving it will push you into uncharted territory. In the case of my father’s greenhouse, this unknown territory was a garden with steep terraces.

How to build a greenhouse on a steep slope?

To make matters worse, the ground sloped in two directions, falling generally to a single point at one corner of the greenhouse. This seemed like an impossible obstacle, but slowly a viable solution emerged. With a bit of effort, we figured out how to place the base of the greenhouse on one plane (albeit at an angle).

Once this problem was solved, the next problem to solve was how to deal with rainfall. Water flowing off the roof and hitting the ground would naturally flow down the slope, which could cause erosion. We compensated for this by combining terraces with a sloped greenhouse. The terraces slowed the flow of runoff and allowed water to infiltrate rather than destroy the landscape.

Although the system wasn’t perfect, it worked. And that brought an significant question to my attention. If I could build a greenhouse on a sloping site where runoff was a problem, could I somehow apply the slope and runoff to my advantage? In tiny, can the problem become a solution?

Installing a sloped greenhouse system

My job at Clemson University provided the perfect scenario for testing greenhouse systems. We wanted to build a modern greenhouse and relocate some older existing greenhouses to a suitable area closer to other farm buildings. The lessons I learned building my father’s greenhouse convinced me that greenhouses could be built on a slope to capture more winter sunlight and apply the slope to collect rainwater.

The chosen location was slightly sloping towards the west and connected to the parking lot, office, harvest area and market building. The site required complete landscaping and a water management system to keep the parking lot and buildings arid. While working on the greenhouse plans, I spent several additional days developing a comprehensive plan to capture and apply water leaking from the buildings and parking lot.

The inclined surface compared to the horizontal surface shows the percentage enhance in the amount of sunlight reaching the inclined surface compared to the horizontal surface. Solar radiation on a tilted surface shows that as the slope increases, the amount of direct solar radiation a site receives also increases. Analysis carried out using a calculator on the website www.pveducation.org.

Sloping the land towards the south catches sunlight and water, but too much slope causes erosion. So I chose a slope of 1%. This gentle slope – dropping 1 foot in 100 feet – catches a bit more sunlight. However, it is not steep enough to cause the seeds and soil to be washed away.

Creating a slope

To create the slope, we collected dirt from areas that would become water-holding ponds. Due to the natural west-facing slope of the land, we would have to move a huge amount of earth to create a perfect south-facing slope. To reach a compromise, I decided to create a two-way inclined platform, grading the land towards the southwest and maintaining the existing western slope.

Because we were building five greenhouses over a immense area, we built cascading ponds to accommodate two slope directions. The dam of each pond became a path to the entrance or between the greenhouses.

We placed the ponds on the south end of the slope to capture the airy reflected from the greenhouses during the winter. Rainwater flowing from the greenhouse flows down into the ponds. The sizes of the ponds are adapted to our climate; therefore, rainwater alone is enough to replace natural evaporation and keep the ponds filled.

Orienting the greenhouse on a slope

The finished greenhouse platform slopes south from B to D and A to C at 1 percent and from B to A and D to C at 1 percent. Water flows into a reflecting pond on the south side. The greenhouse arches will be attached to metal pins along the edges. Sturdy landscape fabric installed in the beds prevents weeds from entering.

In winter, the angle of sunlight becomes smaller, and this effect is greater the further north the property is located. An east-west orientation is always best for a greenhouse of any size or shape because it maximizes the capture of solar energy. The east-west orientation prevents low-angle sunlight from reflecting off the greenhouse plastic instead of entering the interior.

However, placing multiple greenhouses in an east-west orientation is challenging because each greenhouse can cast a shadow on its neighboring greenhouse. The effect of winter shade increases as you travel north, requiring even greater distances between greenhouses.

40 degrees latitude is the point at which an east-west orientation is the only choice that makes economic sense. If you build multiple greenhouses in an area south of 40 degrees latitude, you can place them in a north-south orientation without losing an economically significant amount of solar radiation. The north-south orientation allows for much closer spacing without worrying about shadows, and that’s what we opted for at Clemson.

Greenhouse orientation matters

When building greenhouses on an inclined platform, position the platform towards the south. This way, the greenhouses will absorb more solar energy, and rainwater collected on the south side will reflect more airy into the greenhouse in winter.

The orientation of the greenhouse relative to the slope affects how water will drain into the pond. If your greenhouse is located in an east-west orientation on a south-facing slope, you must direct water that runs off the north side of the greenhouse around the greenhouse and into the pond. If your greenhouse is oriented north-south, water runs down the sides of the greenhouse and straight down into the pond.

Greenhouse on a slope: building a platform

Building a sloped greenhouse platform requires planning and grading. In tiny, the process is as uncomplicated as determining the direction and percentage of the slope of the land, calculating the amount of soil needed to change the slope, then setting up grading stakes and actually moving the soil.

Featured Video: Greenhouse Tips and Ideas with Shawn Jadrnicek



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