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The late Fall and Winter growing season is upon us and if you haven’t already, it’s time to take some steps to keep your greenhouse running at peak capacity.  Undoubtedly, one of the most challenging times for growers in the North is the period of progressively shortening days, lower light levels and falling temperatures, so everything that we can do to minimize this season’s effects can keep your bottom line as healthy as possible.  

Best practices of “winterization” should include maintenance of your structure and systems but also include modification of your crop production practices and schedules.  


  1. Inspect, service and test all heating systems.  This includes secondary ventilation systems as well as environmental controllers.  Be sure that your fuel is clean and well stocked.  All heat exchangers, motors, pulleys, etc should be inspected and repaired/replaced if necessary.  Backup heat source(s) should be considered mandatory.

  1. Examine and secure greenhouse glazing/cover. Be sure that glazing material (double poly, poly carbonate, glass, etc) is properly secured and flashed.  A simple hole in the poly, loose glass, or detached polycarbonate will be a constant source of heat loss, resulting in lost revenue and potential damage to your structure.  
  1. Repair or replace flashing around doors, vents, and shutters.  Not only will improper/damaged flashing and weather-stripping cause heat loss, but is also a common access point for mice, rats, and other rodents.

  1. Maintain and service your dehumidification equipment. While most growers do not pay much attention to ventilation systems in the winter, your vents, fans and louvers are critically important to lower wintertime humidity levels, control VPD and provide proper air exchanges.  Failing to lubricate louvers, for example, can cause them to not close properly, allowing several air exchanges per hour.  
  1. Inspect lighting/change bulbs if necessary. For growers using HPS lighting, cleaning bulbs and reflectors is mandatory and replacement should occur before recommended lifespan is reached.  Older bulbs will burn electricity while providing less than optimal lighting and even a small amount of dust on reflectors can diminish light diffusion and intensity.
  1. Utilize C02 for maximum winter growth.  For growers utilizing C02 supplementation, burners or orifices should be cleaned and replaced if necessary.  Any grower not utilizing C02 should consider including it in the winter months.  At a very low cost, simple combustion C02 supplementation can boost yields by up to 20%.


Adjusting your crop schedules.  During the fall and winter months, you must take into account the fact that the shorter days and lower light will cause crop growth to slow down.  When growing sequential crops, such as weekly leaf-greens in an NFT system, a crop that takes 6 weeks from seed to harvest in the summer may take upwards of 8-10 weeks in the winter.  Adjust your weekly seeding rates accordingly to accommodate for this growth shift.  

Don’t neglect root zone temperatures! While ambient air temperatures may be maintained in the proper ranges, cool spots under benching or nutrient solution temperatures that are below ambient air temps will slow down crop growth and affect quality.  Be sure that Horizontal Airflow Fans (HAFs) or Downdraft Fans are properly employed to provide a very even and uniform air temperature within the greenhouse.  Insulate any underground nutrient solution reservoirs and provide nutrient solution heating to keep nutrient temp at or above ambient air temps.  

Provide correct germination and propagation temperatures and lighting.  Always maintain correct germination temperature for your given crop. Far too often, we see growers neglect appropriate germination temperatures and growth suffers.  A 5% slowdown in germination rates can adversely affect uniformity, quality, and overall growth rate for the entire life of the crop.  All propagation systems should utilize bottom heat and appropriate supplemental lighting.  Most leaf crops in seedling stage require at least 17 moles of PAR per square meter per day for proper development.  

Proper light and temperature = proper growth and good crops!

Increase nutrient concentration.  With lower light levels come lower transpiration rates.  Increase nutrient solution concentrations between 20%-40% over summer usage.  

These simple steps should be incorporated into your yearly production cycle.  While each is seemingly small, they can provide tremendous benefit and cost savings to the grower.  Conversely, neglecting these critical items can be very detrimental to your overall crop growth.  Take the time to properly maintain your structure, systems, and crops and they will take good care of you.  Best of luck and Happy Growing!!

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