in july in michigan it gets warm, and occasionally gets hot. it feels like heaven compared to summers spent on my native eastern shore, where it felt like you were swimming though humidity, and the sun would often beat down at 98 degrees for weeks on end.
while it might just be warm outside, it gets downright hot in the greenhouse, especially given it’s less than adequate venting system. to cool greenhouses, two normal methods are used. the first is to cover the whole thing in white latex paint. the first summer i worked at the farm we did that, and my boss ended up being covered in more paint than the greenhouse and it took three days up on a ladder to finish it. the theory is that it flakes off during the winter and then is ready to go before spring arrives. of course in addition to the time and mess, i also don’t like the idea of spreading all that paint around the greenhouse even if it is low in toxicity.
the other solution is the use of shade cloth. it comes in various degrees of shade, but 30% is pretty common. it reduces the amount of light that can be transmitted into the greenhouse and does a good job of keeping the house cool. it also limits the amount of sunlight that the plants are getting drastically, which is not really a problem this time of year when we are having 16 hours of sunlight, but if we have several overcast days in a row, you need to pull it off. so one of the major disadvantages of shade cloth, but also an advantage is that you have to pull it one and off. for us the issue of utilizing shade cloth is that it can’t really go over a ridge vent like the one we have in the greenhouse. it puts too much weight on the vent, and also inhibits the ability for it to vent properly.
our not so good solution. shade cloth inside.
we drap the shade cloth over the benches that we normally grow on top of. the shad cloth is not long enough to get all sides, so we make sure that it covers the south side where we get the most intense sunlight.
the plants stay cooler and don’t dry out nearly as quickly, but they certainly are not as cool as they would be if we covered the whole house in shade cloth. because they are growing under shade cloth they tend to be a bit legger than those grow in direct sun, and they tend to be a little weaker, so hardening off is extra important. people actually seem to like these shade grown transplants, because they have so much lush, leggy growth. these get distributed this week, so very soon our greenhouse care needs will be much much less.