Solar Garden Beds

Solar Garden Beds 2014-2015
Linton Springs Elementary School, Carroll County
Guest Post by Anna Letaw, UME Master Gardener

The raised bed is 4’x8’; along the perimeter, 2”-foam insulation goes down into the ground about 18” providing insulation from frost.  The lids have two layers of “glazing”, a specially-designed, fiberglass-reinforced plastic sheeting material, and it has a layer of translucent fiberglass “angel hair” insulation sandwiched in between.  Though the sheeting material admits the full-spectrum of light, the angel hair insulation reduces the amount of light coming through (which, according to Poisson, helps moderate temperature swings).  The plywood ends have a layer of 1” foam insulation.

We have three of these beds and the total cost for the project was about $3,000.  We received two grants, one local and one from Whole Foods, to purchase the materials. 
 Nov. 25, 2014: Just planted: lettuce, beets, kale and spinach
 Feb 22, 2015: Day after snowstorm that dropped 12″ snow.

Feb 27, 2015: Plants are quite happily growing away.

Knowing how well these heat up, I left the snow on top of the lids after the Feb 21 snowstorm.  The next day the snow was off and I had to prop open the lids.  Often, if I got down to the beds by late morning, there would be a cloud of steam escaping as I raised the lids!  I tracked soil, external and internal temps from about mid-Jan through mid-Mar.   Soil temps appeared to range from @35-45F but generally hovered around 40F.  Internal temps were interesting: one min reading was -6 outside and 15 inside, and a remarkable max reading was 49F outside, and 109F inside!  Though the condensation is supposed to roll back into the bed, I found I needed to water the beds periodically, especially as the weather started to warm up.

While this is an interesting project, I found that harvesting lettuce for the school in the middle of winter is not for kids, nor for adults.  These were planted in an intensive manner and I only wanted to harvest the outer leaves so the plants could keep growing.  It was a time-consuming task and though I was dressed for the weather, my fingers had little protection and they got very cold, very quickly.   The greens were sweet until about Mid-May and I harvested about 3 times.  Because of timing and activities, a lot of it ultimately went to waste and I need to figure out better scheduling.

This is one of our cafeteria offerings.  The sign reads:
From Our Vegetable Garden:
STAR Garden Salad Mix
Leaf lettuce, beet greens, kale
and spinach!
Guaranteed to fuel your brain and body
& help make you smarter – all day long!


This is Mid-April.  Note the “solar cone”, same concept as a cloche but made from the fiberglass sheeting.  It did a great job for our tomato!  I started a bush tomato inside and on Apr 15 I transplanted it outside.

This project was based on the concept by Leandre Poisson in his book: “Solar Gardening: Growing Vegetables Year-Round the American Intensive Way”.
You can read more about our Solar Gardening Project here:


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