Horticulture Tip of the Month: How to Turn Down the Heat

Tip of the month leafFrom The Best of Ask Ed: Your Marijuana Questions Answered

“We are growing in an enclosed room under a single 1,000-watt high intensity discharge (HID) lamp. We are struggling to keep the temperature under 90° F with fans going continually and an open door during lighted hours. We have an air conditioner in the room, but after 30 minutes it just spews out hot air. We’ve read that cooling the roots may be the answer to our problem. What do you suggest we do? Will the plants survive in 90° F conditions?”

High Temperatures will not kill the plants as long as the roots are kept moist. However, it will ruin the flowers, which will be loose and sparse along a stretched stem. Therefore it is essential to keep the room in the low to mid 70′s F (about 24°  C) with unenriched air below 82°  F (27° C) when the air is enriched with CO2.

An easy way to eliminate the heat would be to stop it from getting in the room. An air-cooled light vents most of the hot air created by the bulb. This air never enters the room. It is drawn from outside through a tube, is heated in the reflector and removed through a second tube. It has no conspicuous odor and can be freely vented.

A single 1,000-watt lamp creates about 3,200 BTUs of heat. A room air conditioner (the kind that goes into a window) can be used to move the heat out of the room, either outdoors or to another space, such as a room or hallway. For convenience, a portable air conditioner can be rolled into the space when needed. It vents heat out through a 4-inch tube.

Changing the light cycle so the lights are on at night and off during the day can be a solution. Depending on the area and season, nighttime temperatures may be much cooler than daytime temperatures. Cool outside air could be vented into the space and hot air removed.

There are many reports about cooling or heating roots to counteract above-ground temperatures. If the canopy temperature were 85° F (29°  C), the roots would need to be cooled to 65° F to counteract the hot air. In a hydroponic garden, this can be accomplished using an aquarium water chiller. However, there is a learning curve involved.


51oOAbmb2aL._SX331_BO1,204,203,200_- Ed Rosenthal
From The Best of Ask Ed: Your Marijuana Questions Answered

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