Sunday, January 22, 2012

Winter Greenhouse Systems Part I: Reemay Revisted


How can you grow vegetables in the winter?  Don't you need to burn a ton of fuel to keep the greenhouse hot?  These are some of the questions I often hear when I tell people I work on a farm in the middle of January.   I think one of the most interesting and common misconceptions about winter greenhouse farming is that the greenhouse needs to use a lot of heat to grow food.   The truth is plants are incredibly resilient and creative organisms that find ways to not only survive in cold temperatures, but thrive in changing environments.  Spinach and carrots for example go through a process of converting starches to sugars to adapt to the fewer hours of sunlight during peak winter months.  This produces a healthy plant and creates an even sweeter taste that is more attractive to people.  What I find most incredible about the greenhouse I work in at Stone Barns is that even though the soil is directly in the ground and not in soil pots or benches, the deeper soil levels naturally maintain a temperature roughly in the 45 degree level where as the ambient temperatures can reach below freezing if not heated.  Understanding these basic soil facts allow us to work with earth's natural heat to create an ideal growing environment while maintaining a very low energy input usage.  We are attempting to produce produce that is best suited for the natural environment we are growing in and by keeping the surface levels of the soil just above freezing, we can grow fresh food all winter long.  So how do we keep the soil levels above freezing if the ambient temperature can drop below freezing?  Last year we discussed the benefits of...
Reemay and the sea of white blankets that covers the 1/2 acre greenhouse each night throughout the deep winter months.  This year, as the sole greenhouse apprentice, I had the pleasure of actually cutting and assembling these blankets with some of my fellow farmers and there really is no better way to gain an appreciation for something than by diving in and participating in the whole process (Hats off to all my former winter greenhouse apprentices).  Before coming on full-time as a greenhouse apprentice, I would show up on Saturdays and the reemay would usually already be hanging up on the bungee cords, sometimes I would help tie it up or lay it back down over the beds at night, but I never realized just how much effort went into this process each and every day.  But as with everything, through struggle comes strength and after a few days of fumbling around the system begins to get easier.

Looking back at the cutting  of ten 90 ft strips of Reemay for the 2012 winter blankets, you can see how important teamwork can be.  A job that would have taken many hours alone was turned into a simple a fun project with the addition of a couple of knowledgeable and willing helpers.

Some chalk, scissors, a tape measurer and a pare of sweet lady bug boots and the job gets done in no time.  Setting attainable goals is also an incredibly important part of creating a positive and rewarding work environment.  There have been many times when I find myself setting arduous and unattainable goals for accomplishing more tasks than I will physically have time to handle.  In the end that type of planning only leaves room for increased stress and unmet expectations.  Keeping it simple, manageable and within reason are all important.

Once the pieces were cut, using these bungee cords, featured below, we tied up the long 90ft strips of Reemay while placing a metal wire every 12ft along the bed path.  An integral part to this process,

the metal wires are used to ensure that the Reemay doesn't sit directly on the plants or soil.  As we know, Reemay helps retain heat and also holds in moisture.  Although we want the heat, we don't want to have a major buildup of moisture as this can lead to unwanted fungi, moss and pest problems.

I think the simplest way to understand the positive effect of Reemay is that by putting these blankets over each bay, we are creating a greenhouse within the greenhouse.  We know that greenhouses control climate and retain heat by having an enclosure over the plants.  This is important in the winter because we want to retain as much heat as possible since the amount of sunlight is so low between the winter solstice and the spring equinox.  The placement about a foot above the plants, allows enough heat to circulate between the soil and the blanket keeping the ground from freezing.  Along with the Reemay covers, we have some incredible and technologically advanced 99% efficient automatic heaters by True Leaf that provide both heat and carbon dioxide to the plants and soil.  These heaters turn on anytime the greenhouse ambient temperature reaches below 35 degrees.  This slight adjustment in temperature coupled with the natural 45 degrees underground allows us to use as little propane as possible while maintaining a reasonable temperature for the plants to flourish.


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