Dealing with heat issues in the desert...

Discussion in 'Plant Problems' started by Rusty Trichome, Jul 27, 2008.

  1. Rusty Trichome

    Rusty Trichome Registered+

    Below is what I do for my soil grow during our hot summer months in the southwestern desert. I have never grown hydro, so am unable to verify any of this for anything other than soil grows.
    My flowershed is an outdoor shed approx 8' x 12' x 8' tall, of which a quarter if it is for growing. (no, it's not a metal shed)

    In my humble (sometimes) opinion, "must keep temps below 80" is a guideline, especially appropriate for beginners.
    Being anal about it is truly unnecessary. Ambient temps inside my outdoor growshed (2 x 400w HPS's) often reach the low 100's. This is including having the window A/C unit on 'high'.
    Does it slow the growth...? Yes, a tad. Delays harvest about a week or so. However the yield is there and the quality is there.

    First technique I learned
    ...quit hanging the thermometer by the canopy top. Was too depressing and stressful. All of my temps listed are ambient room temp, taken from the side of the grow, about 5' off the ground. I use the 'back of the hand' method of determining canopy temps. If it's not too hot for me after a minute or so, they'll be fine. (change hands often when doing this, or go around with one hand tanned, one hand not tanned)

    Window A/C units.
    When using a crappy window unit A/C, and it's real a vent or window, just a crack. (the higher the vent, the better) Trapped, heated air doesn't cool very well.

    Never overfeed when hot.
    ...don't feed full-strength nutes all at once. Split it up into a couple of 'light' feedings equaling the same nute intake per week as recommended by manufacturer. Example...Instead of giving once-weekly nutes at 2 tsp per gallon, give 2 feedings at 1 tsp per gallon. (I give mine on mondays and thursdays) On the other days, I add either plain ph'd water, or micronutes, per my schedule. (Fox Farms) The strongest additive I put in the potting soil prior to use is worm castings and michorrizae fungi. I steer-clear of manures. (not so during the winter months)

    Never spray with the lights on. Each drop of water sitting on the leaf acts just like a magnifying glass, and it will burn the leaf tissue. Flowering ladies prefer the lower humidity anyway. Spraying will also increase possibility of mold. You'd be amazed how long a drop of water can remain sandwiched between two leaves. Be careful watering on hot-muggy days, as it will increase your humidity levels, which can also increase chances of mold.

    Ditch the intake fans unless it's hooked-up to an A/c unit.
    You can add all the intake fans you want to add, and they will never work like having a strong exhaust, placed high to remove nothing but the hot air and cannabis scent. The suction caused by having the exhaust on, pulls-in the exact same quantity of air that's going out. (physics - nature abhors a vaccuum)

    Stagnant air traps heat and provides no fresh oxygen or CO2.
    I usually have two dedicated 'oscillating budfans' which I keep on 24/7. One on either corner of the front of the grow. Both are pointing at a slight up-angle, but one is only for the space between lamp and canopy, the other blows 'thru' the plants, providing fresh air to soil, and removing any stagnant heat. Obstructions (unnecessary shit in the room) can and will trap heat.

    Lamps and plexiglass.
    I don't have a cool tube set-up, but when it's just too hot at canopy top, I do hang a 3/8" plexiglass sheet horizontally above the ladies, (just below the lights) to block the direct heat from the lamp.
    If nothing else works to keep the temps within 110, I break-down and raise the lights a bit. If it's still over 115, I'll shut the HID's off, and turn on some 23w CFL'S (soft white) to keep the light schedule on target. I don't know if this is a benefit, but it makes me feel better.

    This is all I can think of right now, but if y'all have any questions...fell free ask.
    • Like Like x 8
  2. should

    should Registered+

    Thanks for the thread rusty, ill have to try some of those techniques... its sad looking at the thermometer and seeing high 90s :(
  3. lunarose

    lunarose Registered+


    I have the same problem this time of year in my greenhouse. I have been reading about smartpots and think I'll probably give them a try next year since they are suppose to help keep the roots cooler.

    Another tactic that has worked for me is to cut a piece of that weed blocker fabric with a hole in the middle for your plant and then cover it with a layer of straight perlite.
  4. Rusty Trichome

    Rusty Trichome Registered+

    My pleasure.
    Keep in mind, I do not recommend anyone purposely raise the temps in their growroom to these extremes. These are methods to help keep temps reasonable enough to get quality results from a very harsh enviornment. :thumbsup:

    Would put some more thought into the SmartPots. Thoughts does the pot cool the water, or at the very least, not retain ambient heat? The water will act like an insulator, collecting external heat. Or at the very least, not let the heat escape. Also, cannabis doesn't much like being fed from the bottom. At least mine didn't. (no fresh water to upper root zones, and conditions that virtually guarantee root rot in the lower root zones)
    I'm a bit doubtful the cloth and perlite are necessary, but...If it works, stick with it. A fan blowing across the pots will circulate air and should cool the roots just fine. (unless your greenhouse is sitting in the middle of an asphalt parking lot, lol)
  5. lunarose

    lunarose Registered+


    Thanks for the heads up on the smartpots I had posted asking about them and had not gotten any answers.

    I have a nice 20" fan running in there now and that has really helped.
  6. Opie Yutts

    Opie Yutts Registered+

    Wow, I didn't realize even growing weed in 115 degrees was even possible.
  7. Rusty Trichome

    Rusty Trichome Registered+

    Me either, till I was forced to make it work. :jointsmile:

    It's not something I look forward to every year, but at least I don't panic when temps start to rise in the spring. If my wifes church friends would quit coming over unannounced, we could move the flower room indoors too, lol. Oh well...they're good people. Gotta take the good with the not so good.

    We have two seasons here, (summer and winter) with two week grace periods between them. Now, I'll almost regret the cooler temps. It's actually cheaper on electricity trying to cool the flower room in summer, than it is to heat it during the winter. ($100.00 per month more during winter)

    I might be doing a 4 month veg this winter, tho. If I can swing it, I'll just take my MH light out to the shed, and keep 'em on 24/7. Gotta heat the room anyways, might as well do it with HID lumens. :thumbsup:
  8. painretreat

    painretreat Registered+

    Dealing with heat issues in the desert....

    RT-thank you so much. I've been waiting to read something like this. I get snow and heat; little in between and the heat with a grow is making me nervous as heck. pr :thumbsup:
    • Like Like x 1
  9. Rusty Trichome

    Rusty Trichome Registered+

    My pleasure. Anything I can help with, just ask away. :thumbsup:
  10. darrenlayo

    darrenlayo Registered

    Am having major heat problems myself. Only on my second grow and have just set myself up another tent for starting my seedlings and veg. I have a 1.2 x 1.2 x 2m tent laying down on its side with 4 x 200w CFL's in one shade. Couldnt believe how hot these lamps were getting but am mainly putting it down to them being self ballasting. Anyway only planted the seeds 2 days ago. When i checked the thermometer the temp had reached a maximum of 40c/104f. Hooked some decent extraction up straight away and now have it down to 33c/91f. Am growing in soil on 18/4 light and dont have any sprouters yet. Are these high temps gunna stop my seedlings from sprouting?
  11. Rusty Trichome

    Rusty Trichome Registered+

    4 200w CFL bulbs in one hood? Wow. Might need to use the vaccuum to suck-out that kind of heat, lol. Do you have to run all 4 at the same time, or can you unscrew one or two till plants harden-up to the heat? (a week or two)

    Seedlings don't need light till they break the surface. But yes, 91 is likely too warm. Would move 'em asap, or turn-off the lights. (but turn 'em back on when they sprout) 80ish is max I recommend for germinating seeds.
    Have you tried different combinations of lights? Finding out what you can do to lower temps when ambient room temps rise, is a good thing. You can remove one light, or angle the bulb so they are closer together when lit, or further apart, or another fan when necessary. Try different things to see what is the best you can do when it gets hot.

    Every growbox, growcab, grow shed and grow room are different. Different shape, volume, different contents. There is somewhat an optimum set-up for each. You have to fiddle around till you find the best 'cooling' technique for you, and use it when necessary. Tiz a good idea to check the temps in different locations of the growtent, too. Dead spots (trapped, stagnant air)heat up quickly.
    • Like Like x 1
  12. darrenlayo

    darrenlayo Registered

    Thanks. have unscrewed 2 of the bulbs and raised the hood a little. has bought the temp down to 28c/82f. have 10 seedlings all in 11 liter pots and it looks like there is still sufficient light. have 1 sprouter now so hopefully most of them will pull through.
  13. McToker

    McToker Registered+

    Rusty ~ Thanks for the great thread. I guess I was just beating myself up trying to reach that "ideal" temp. We're in the same climate as you but working indoors in a Homebox. We finally gave in an turned off some of the fans scattered around the area, outside the box, and just cranked the A/C down a bit.

    I like your idea about the sheet of plexiglass.



    • Like Like x 1
  14. xRedDUBdeRx

    xRedDUBdeRx Registered+

    Good post. Im west coast indoor grower here and nothing but desert! Will be helpful next spring/summer =P

  15. brainfood33

    brainfood33 Registered+

    This is the most perfectly timed thread I've found so far, thank you so much for this info.

    I'm not in the Desert, quite the opposite in fact as I am in the Northern UK and we rarely even see the sun! lol
    But I do have heat issues whenever I switch on my second 600W HPS in the flower room as the temps climb from the low 80s with 1 light, to the high 90s when both are on.
    This has lead me to limit myself by only using half of the room which really isn't enough for what I need.

    I have a powerful exhaust fan with a carbon filter and plenty of circulation but I've been scratching my head to figure out what I can do to reduce the temp with both lights.

    I was contemplating putting in an intake fan but there are too many difficulties involved with bringing the air in by stealth and this was worrying me.
    But you seem to not rate the value with them anyway?

    My main question here though, is that I usually grow hydroponically and will be doing so when using both lights in the future.
    Why would it be any different for hydro than for soil as you stated in your opening sentence?
    Is it to do with the root systems not having the protection of the soil or do the plants in general behave differently between the 2, maybe more sturdy when in soil?

    Cheers! :)
  16. Rusty Trichome

    Rusty Trichome Registered+

    True, I'm no proponent of using an intake fan, but I do realize there are times that one may be necessary. If you have good exhaust, a simple intake hole, (or two) the same size as the exhaust hole is sufficient.

    I have not had any experience in going hydro, and thusly don't want to represent that these 'techniques' will work that way. I try never to comment on techniques I've never personally tried before.
    The main thing I'd worry about, how to keep the reservoir cooled enough not to harm the roots.

    Have you thought of using a light mover?
  17. brainfood33

    brainfood33 Registered+

    Despite preferring not to comment on Hydro, I think you might have answered the question. :)
    It will be an issue indeed that the reservoir temps will be too high, and therefore very warm water will be feeding the plants continuosly which is not a good thing at all.

    A light mover would be the ideal solution but I'll have to save up for one as I am totally broke at the moment sadly. Can't even buy any green! :(

    I guess another option would be to master the soil grow and ditch the hydro altogether, now that I know that hot temps aren't so scary afterall.

    Hmmm, no reservoir, no buckets, no ridiculous amounts of water, no pumps, no rockwool... its sounding good already!

    Cheers again Rusty.
  18. Rusty Trichome

    Rusty Trichome Registered+

    No problem.

    Altho I've never grown hydro, I have had friends that were mighty proud of their accomplishments using it. I was always under-impressed. They looked great while growing, and I guess it got you high ok, but were lacking in flavor.
    I much prefer my soil grow. To me, it's easier and cheaper, no risk of clogs or fittings coming loose. Others proclaim it's advantages, but it's just not for me.
  19. Obscurus

    Obscurus Registered+

    Excellent thread

    This is a very great thread. It gets over 100 out here in NM during the summer sometimes, and I was definitely concerned about the temperature a lot more than I should have been I guess. I was also keeping the Hygrometer near the canopy of the plants.. I am going to move it and see what the ambient temp is like.

    Thanks for spreading the info!
  20. mojavemama

    mojavemama Registered

    Great Thread!

    I'm a desert grower, but decided to experiment with an indoor-outdoor grow.
    It's labor intensive, but I've found ways to compensate for the lack of humidity and intense sun and heat.

    My girls are all in 3 gallon pots, 5 of which fit into a rolling garden cart. I fill the bottom of the cart with river rock, then add an inch of water to help with humidity.

    Then I wrap each pot in layers of wet newspaper, and lay strips of wet newspaper on the top of each pot's soil. Only the leaves are now showing. I then cover the sides of the cart with shadecloth, so the cart itself won't get so hot.

    The plants have been out every day, in temps reaching 104 degrees, and have done fine, showing no stress. The soil is always cool when I check it.

    About 3 pm, it really gets super hot, so i move the plants into the shade until sundown, when I take them all inside, and put them in my grow room. In the grow room, I have a humidifier that keeps the room at about 60% humidity, and it's also air conditioned, and has a good sized overhead fan.
    I'm now into 12/12 flowering, and still letting the plants stay outside during the day. They are very healthy and happy, in spite of the intense sun and desert heat.

    But like others have already said, never let the soil get too hot or dry. Overwatering is not normally a problem here in the desert. My plants drink about a gallon a day each.

    Here's a picture of some of my plants in the desert sun. You can see they are green and healthy, in spite of the direct sun on them most of the day.

    Attached Files:

    Last edited: May 22, 2009
    • Like Like x 2

Share This Page