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Modernization: Which is the right retrofit?

When upgrading your existing greenhouse, be sure to have clear goals in mind to avoid needless spending.

November 12, 2019  By Duane Van Alstine

Not only can flood benches help to reduce irrigation and fertilization costs, they can also reduce incidence of disease. Photo credit: GGS

This is the time of year to begin planning for next year’s greenhouse building projects. While many growers are eager to plan new construction projects and expand, sometimes the best dollar value is achieved by retrofitting and modernizing their existing greenhouse structures.

To ensure retrofits are being installed as efficiently as possible, it’s important for the grower to know foremost what they’re hoping to accomplish.

Typically, reasons for retrofitting fall into three buckets: improving crop, reducing costs, and producing more. In today’s economy with labour shortages throughout North America, there’s often a fourth goal in driving greenhouse improvements: increasing labour efficiency.


The following are problems already faced by many growers, and they can be resolved by simple improvements on already existing structures.

Targeting labour efficiency
One of the biggest expenses for growers today is labour, so it’s vital that an employee’s valuable time is used as efficiently as possible.

Increase automation. Environmental factors including irrigation, fertigation, ventilation, shading and lighting can all be automated with simple or more complex control systems. Rollup sides are another area that can be operated with a motor and connected to your environmental control computer. Any areas in your greenhouse where employees still have to manually adjust the environment takes away valuable time from more important plant care tasks including disease inspection and pruning.

Improve ventilation. Adding more ventilation or just HAF fans to move more air around the greenhouse is a quick and fairly inexpensive way to improve production. If the greenhouse gets too hot in the summer not only will it affect the plants, but it will also affect the employees. Creating a more comfortable work environment will result in a more productive workforce. Most ventilation upgrades require fairly simple installations and will not disrupt production.

Use transportation carts. Double-rail carts on heating pipes span the width of a greenhouse and can dramatically reduce employee travel time while picking and packing. Trolley carts in the main aisle can be loaded and moved from greenhouse to greenhouse, filling it on the way to the shipping area.

Process mapping to redesign layout. When a grower analyzes the lifecycle process within the greenhouse, it may show that changing where aisles are located, or rearranging benching layouts or production zones, could reduce material handling and employee travel time.

Increasing production
More efficient production doesn’t necessarily involve adding more structures. It can be realized in an existing greenhouse with a few simple retrofits.

Installing rolling benches to replace stationary benches is a simple way to increase production without losing any crop production. Rolling benches remove the need for a dedicated aisle between every bench, adding about 25 per cent more growing space and enabling employees to move more efficiently between them.

Flood floors are an excellent option for reducing aisle spacing, packing in more plants per square foot. If there’s enough area to justify it, robots can also be installed for adjusting pot spacing on the floor to make sure everything is being watered as efficiently as possible. Growers should be aware that flood floor installation requires that everything is moved out of the greenhouse, which will cause a disruption in production.

Reglazing the roof is part of the regular maintenance schedule when growing in a poly greenhouse, but even 8mm PCSS roofs, acrylic and glass structures can become damaged or dull. Growers should review their roof glazing and consider the light levels necessary to get more production out of their greenhouse.

Supplemental lighting and shading. If the flowering cycle of your crops can be manipulated by adjusting light levels, then supplemental lighting and a curtain system are ways to get an extra crop out and can even provide an opportunity to better time market readiness for the next buying season.

Improved crop environment
Greenhouse technology has improved and an older greenhouse may not be providing the best environment possible to maximize production.

Increasing ventilation in a greenhouse is one of the simplest and most cost-effective retrofitting methods used to improve the environment for crops. Rollup curtains can be added onto any hoop house or poly end walls and can be manually operated or automated with a simple motor. Hard glazed sides and ends can also be fitted with vents, and in most cases the existing sidewall glazing can be reused. Gutter vents and ridge vents can be added to most greenhouse arches easily and with a little expertise. Adding more ventilation to your greenhouse structure allows better flexibility for your growing environment, reduces humidity, increases airflow and helps to strengthen the plants.

Raising the roof of the greenhouse may help to improve the growing environment. This option can sometimes be more costly than building a new structure from scratch, but it is a quicker process. A qualified greenhouse builder with experience in raising greenhouse roofing should be involved in this kind of project. Modern commercial greenhouses are being built with 16 to 24 feet under gutter heights.

Reduce Operating Costs
Install energy curtains. More growers are choosing to install energy curtains for the improvements they can make to the greenhouse environment and for the significant energy savings. By keeping the heat in through the winter and by shading the greenhouse through the summer, growers can see energy savings of between 20 and 40 per cent when used in conjunction with their other environmental controls. Curtains can easily be installed and are an excellent option for growers looking to retrofit their greenhouse to save on operating costs.

Check ventilation. Over time, the rubber seal around vents may need to be replaced as they can become brittle or malformed due to sun exposure, rain, wind and snow. Vents that aren’t sealed properly will negatively affect their operation and will cost growers money as the heat is directed out of the greenhouse. Roof ventilation in modern greenhouses uses EPDM (Ethylene Propylene Diene Monomer) rubber, which is more durable than other vent rubbers.

Flood benches help to control irrigation and fertilization costs. By recirculating the water, unused fertilizer is available for the next cycle. It’s an environmentally friendly option that also helps to lower disease in the greenhouse by keeping the leaves dry. The savings in water and fertilizer will justify the cost of the benches.

All in all, the kinds of retrofits necessary will depend on the goals of the grower and will differ from greenhouse to greenhouse. Consult professional greenhouse manufacturers to determine what can be done to improve your existing greenhouse as efficiently as possible.

Duane Van Alstine has been in the horticulture industry for 20 years, previously having been the operations manager of a 380,000 square foot facility. In 2011, he left the greenhouse to take on Special Projects for GGS Structures Inc. For more on energy curtains, visit

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