Question
QUESTION: Jacob or Jeff,

I have a question regarding shade cloth for greenhouses. I have a 10x16 hobby greenhouse that I want to put shade cloth on to help keep it cool in the hot summer months for my Nepenthes and Tropical Sundews. What % shade cloth would you recommend for a 10 to 20 degree temperature drop? My greenhouse has 8mm triple wall polycarbonate for the covering...if that helps. I also intend to invest in an evaporative cooler to help keep my greenhouse cool. What methods do you guys implement to keep your Nepenthes/Tropical CP's cool in the summertime while they are growing in a greenhouse?

Thank you,

ANSWER: The type of shade cloth you use depends on the light transmission of your polycarbonate covering.  You should get this information from the manufacturer.  Some polycarbonate covering have 60% light transmission.  If this is the case, then you probably won't need any shade cloth.  Last year we installed a high-density polyethylene covering, and we had about 55% light transmission, so we didn't use any shade cloth at all. Ideally you want about 50-60% light transmission.  So your panels are providing 80% transmission, you can safely use a cloth that provides 20-30% shade to give you an effective shade of 50-60%.  We avoid going lower than 50% because that will affect the growth of your plants.  

How you cool your greehouse depends on your budget and your location.  Swamp coolers are best for dry, desert-like areas or if your humidity is less than 40%.  Some growers have used AC units.  We use a combination of box fans and home-made swam coolers.  We have about 5 box fans and two swamp coolers for a single greenhouse.  We also use fan misters. So we have a shotgun approach - misters, fans and swamp coolers.  When the temperature rises to 100?outside, we can keep the temperature down to the low 80s.  

Good growing!
Jacob Farin

---------- FOLLOW-UP ----------

QUESTION: Jacob,

Thank you for the expedient reply regarding my inquiry. You mentioned some growers using AC units. Do you know of a reputable source for AC units for greenhouses?...make and models perhaps??

Thanks,

Derick

Answer
Since we don't use AC units in our greenhouses, you will need to investigate this on your own.  I'm not sure if those growers were using AC units designed specifically for greenhouses, or if they were simply using standard units found at the hardware store.  Always check with the manufacturer to see if the unit is suitable for a greenhouse and damp locations.