Myths debunked: Directing a fan at a stretched out plant in order to strengthen it.

[LJB]

I keep seeing this advice repeated on this forum and elsewhere, usually when people ask about their seedlings stretching out or flopping over.

The cause and affect part is not a myth. Wind will strengthen a stem.

What many growers don't realize is that this happens at the expense of new growth, new shoots, etc. The plant directs energy towards the stem (and away from other parts) in response to you aiming a fan directly at it. It is the same that happens when a plant has to self-repair damage to other parts.

If your plants are stretching, it's for one of two reasons or possibly both.

(1) not enough light intensity. The lamps are either too far away or don't produce enough lumens or a combination of both.

(2) too much heat around the canopy. Plants will create more surface area in order to increase the rate of transpiration in an attempt to cool down.

Plants don't want to be blasted with direct wind. They want fresh oxygen and co2. You need to exchange the air at a constant rate, either cooling within a sealed grow room or bringing in cooler air into a unsealed room.

(edit: I deleted the stupid analogy)

I can predict that this topic and the way I attack it (bluntly) will cause some people to react emotionally. Don't take these comments the wrong way. I'm not (and neither do the scientists quoted below) saying that directing a fan on your plants is going stop them from growing or disparaging your past harvests, however successful they may have been. This post is about science and facts and providing the optimal environment for plants grown indoors as we're attempting to duplicate the systems found in nature.

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Have a look at this study:

Wind-induced plant motion immediately increases cytosolic calcium

Wind is one of the most unusual and more dramatic of the environmental signals to modify plant development. Wind-stimulated crops are also known to experience considerable reductions in growth and subsequent yield. There is at present no experimental data to suggest how wind signals are perceived and transduced by plant cells. We have genetically transformed Nicotiana plumbaginifolia to express aequorin and thus produced luminous plants that directly report cytosolic calcium by emitting blue light. With these plants we have found wind stimulation to cause immediate increases in cytosolic calcium and our evidence, based on the use of specific inhibitors, suggests that this calcium is mobilized from organelle sources. Our data further suggest that wind-induced movement of tissues, by mechanically stimulating and stressing constituent plant cells, is responsible for the immediate elevation of cytosolic calcium; increases occur only when the plant tissue is actually in motion. Repeated wind stimulation renders the cells refractory to further calcium signaling but responsiveness is rapidly recovered when stimulation is subsequently diminished. Our data suggest that mechanoperception in plant cells may possibly be transduced through intracellular calcium. Since mechanoperception and transduction are considered crucial to plant morphogenesis, our observations suggest that calcium could be central in the control and generation of plant form.

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I can no longer find this one on the internet:

"Studies of the effect of artificial wind on growth and transpiration in Helianthus annulu”

E. V. MARTIN AND F. E. CLEMENTS

It says in part that the depressing effects of wind have long been known. Lemon trees shielded from the wind had an increase in yield of from 5 to 7 times, and an increase in tree size by a factor of 3.

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An excerpt from a lecture delivered at St. John's University - Biology Dept.

Plant Positioning Responses (or Guidance Systems)

http://employees.csbsju.edu/ssaupe/biol327/Lecture/positioning.htm

VII. Thigmomorphogenesis
Plant growth response to a mechanical stimulation such as rubbing, wind, raindrops, etc. The termed was first coined by M. Jaffee. Seismomorphogenesis is specifically the response to shaking.

Compared to unstimulated plants, mechanically-stimulated plants: (a) grow more slowly; (b) increase more in diameter. In essence, they are shorter and fatter. This response makes "sense" to minimize the risk of breaking which is especially true for plants in the mountains. As an example, compare plants grown in indoors (houseplants, greenhouse) with those grown outdoors.

This phenomenon is due to ethylene (the triple response) for the following reasons: (a) ethylene concentrations increase in response to mechanical stimulation; and (b) ethylene treatment mimics these effects, i.e., inhibits shoot elongation and induce stem swelling.

mRNA synthesis is stimulated shortly after mechanical stimulation. Four or five genes are activated, one of which is the gene for calmodulin.

 

[CannabisSativa]

There is no silver bullet....you always have to give up something to gain something and vice versa.

 

[alpinestar]

i agree that you shouldn't direct strong wind at the plants
but a fan is still necessary, and low amounts of wind arent going to hurt growth

 

[Hundred Gram Oz]

2 much nitrogen will also make em stech like strech armstrong

 

[GilligansIsle]

All things in moderation. Remember that a plant is a living thing.

Dood

Here on the Island we believe that "All things in moderation, even moderation" is the way to go.

Safe Harbor
Gilligan

 

[Maj.PotHead]

my fans run 24/7 directly on plants from birth to harvest

 

[CannabisSativa]

Fans are also good because you move foliage...which allows the seedlings to get more co2

 

[LolaGal]

Good thing the wind never blows outside.....! My OD plants would surely be stunted and no count!

 

[VerdantGreen]

If your plants are stretching, it's for one of two reasons or possibly both.

(1) not enough light intensity. The lamps are either too far away or don't produce enough lumens or a combination of both.

(2) too much heat around the canopy. Plants will create more surface area in order to increase the rate of transpiration in an attempt to cool down.

Plants don't want to be blasted with direct wind. They want fresh oxygen and co2. You need to exchange the air at a constant rate, either cooling within a sealed grow room or bringing in cooler air into a unsealed room.

i disagree, genetics are one of the main reasons for stretching at the onset of flower, also repotting plants as you start to flower them will encourage stretch, the reasons you state do apply, but imo arent the main reasons for stretch as most people percieve it.

as for co2, the plant will use up the co2 in the air surrounding the leaf very quickly, so a breeze from a fan will help replenish this with fresh air. just the extraction is not necessarily enough to do this on its own.

but you also dont want a hurricane blowing across your canopy.

Imo, blasting your plants with direct wind in order to "fix" stretching is a bit like treating your own high fever with a fan.

sorry, i dont find your analogy bvery convincing at all.
ive never read about people thinking that fans will reduce stretch, just discourage mould, help strengthen stems in general and replenish co2. and of course help keep the canopy cool.

is someone else said - all things in moderation.

 

[alpinestar]

2 much nitrogen will also make em stech like strech armstrong

have you ever tried N deprivation at the onset of flowering?

you can make sat's look like midgets (with a lowered yield of course - it will cut it in half)

 

[somebody041]

hey LBJ, thanks for posting all of your research in an easy to understand manner... and providing urls!

so do you believe that it would be better to omit a fan from a grow? in my clone/mom room i have a small 7" fan blowing in the corner (blowing at the corner, not the plants), a tower fan in my veg room on a speed controller that blows gently on the plants, and another tower fan (same model) that isnt on a speed controller blowing on my flowering plants. all fans run 24/7. i was thinking, maybe only running them 12/12 would be beneficial. what do you think?

 

[AlwaysLearning]

somebody041, No it is not better to omit a fan from a grow. What you NEED are oscillating fans which gently move the air around the grow room. Having just one fan blowing in one directing wont help as much as having overall air movement. You are shooting for each leaf in the room moving gently in the breeze as a fan passes over it. as LJB said, the plants want to breath fresh air. You also need to be exchanging the air in the room every three minutes or so.

 

[somebody041]

makes sense. i will just point the fans at the walls and turn them up to get as much air movement as possible

 

[vancityj]

One of the main causes of stretching, besides lack of adequate lumens, is too much of a temperature differential in the off-cycle; try to have only a less-than-ten degree difference in day/night temp's to avoid excessive stretching.

 

[rasputin]

Well, not much to add here but thanks for getting a discussion going, OP.

All things in moderation.

Ideally you'll have a moderate amount of fanning all of the time. Strike the happy medium and your ladies will love you for it.

 

[LJB]

There is no silver bullet....you always have to give up something to gain something and vice versa.

That is another way to put it.

i agree that you shouldn't direct strong wind at the plants
but a fan is still necessary, and low amounts of wind arent going to hurt growth

I want to give you an idea of the type of responses that prompted the creation of this thread. There have been more than a handful of threads on this forum and others, usually posted by completely new growers. Their seedlings are 2 inches two tall with one leafseat. They ask why this is happening. Several people reply with a variation of, "you need to aim a fan at them, it will make the stems stronger."

Good thing the wind never blows outside.....! My OD plants would surely be stunted and no count!

Ah yes the wiseguy, or in this case, wisegal response.

A careful reading of the original post reveals not a single sentence that says anything close to "if a fan blows on your plants, they will not grow." In fact, I went out of my way to get across that I wasn't making that point.

See here, my last paragraph before the quoted studies:

Don't take these comments the wrong way. I'm not (and neither do the scientists quoted below) saying that directing a fan on your plants is going stop them from growing or disparaging your past harvests, however successful they may have been.

Considering that any human can see that the opposite is true, I and for that matter anyone in a labcoat would have to be real ass in order to publish anything that says "wind blown on plants = zero growth."

i disagree, genetics are one of the main reasons for stretching at the onset of flower

This thread was originally about seedlings, not flowering plants.

sorry, i dont find your analogy bvery convincing at all.
ive never read about people thinking that fans will reduce stretch, just discourage mould, help strengthen stems in general and replenish co2. and of course help keep the canopy cool.

VerdantGreen, I'm attacking the advice given to growers of stretched out seedlings. The analogy applies when those seedlings are stretched out because of too much heat. But really, who fucking cares? I'm not a writer, I'm an amateur botanist.

hey LBJ, thanks for posting all of your research in an easy to understand manner... and providing urls!

so do you believe that it would be better to omit a fan from a grow? ... what do you think?

No. My goal when putting together a room is to achieve the proper ventilation without fans blowing directly on the plants.

Two examples:

Not sure who the true originator is, but I copied the Prawn Connery (planetganja.com) vertical style of stacking two bulbs and arranging several plants on the floor in a circle around them.

There is one fan in the room, it's one of these industrial deals that can be layed flat:

It's on the floor, in the middle of the plants under the lamps aimed up at them. Hung from the ceiling above the lamps on either side of the 4' x 4' room are two six inch exhaust fans. The leaves that are closest to the fan show visible damage from the strong breeze (I know for fact that this is the cause, and not a nutrient deficiency).

At ground level there are two holes, one on each side lined up with the exhaust fans that act as passive intake and they are cut just above the container height.

In my other flowering room with just one 400w HPS and less heat to deal with, I use a single exhaust fan with two passive intake holes just above container height and also have a little fan on the floor that stands no higher than six inches above the containers for some added air movement under the hood.

I don't mind having a little fan blowing or intake holes aimed directly on the bottom of the stems, but it's for a fresh breeze, not for strength.

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I also second the "happy medium" responses without quoting them.

 

[Maj.PotHead]

One of the main causes of stretching, besides lack of adequate lumens, is too much of a temperature differential in the off-cycle; try to have only a less-than-ten degree difference in day/night temp's to avoid excessive stretching.

4sure what J said
also time in veg and in container when flowering is induced rootball = yield
a well developed rootmass will also help reduce stretch. i mean take a fresh rooted clone place it into a 1 gal bag and flip it lol it'll maybe finish 12-14 inch when startn off 3-4 inch tall. a inadequite rootmass in the container will cause uneeded stretch


alpinestar ---> if you cut N out at the onset of flowering you should wind up with a plant that yellows half way through flower. hence reason why yield is comprimised by approx half

proper way to cut N out during flower is to cut back on N dossage during the first 2 wks for indicas 3 wks for sats.

my veggn plants get 20ml Pure Blend Pro Grow during veg
1st wk of flower they only get 1tsp approx 10ml 2nd wk they get 1/2 tsp approx 5ml by end of 2nd wk they get NONE

i start plants in flower at 20ml Pure Blend Pro Bloom
i find my plants respond nicely to at end of 1st wk flower 1/8th tsp powdered koolbloom and bump to 30ml PBP Bloom
the bump in PK help onset of flowers on my clones faster 10-12 days pinky sized 1's

indicas will stretch 2-3 times average so a 1ft plant onset of flowering could finish 3ft normally between 2-3ft

sativas can and i've seen 3-5times size i've had 1ft plant in 1 gal bag end up 5ft or more just had 1 easy 6ft

 

[BurmeseDragon]

I prefer great exhaust, dust with fans is an issue as well as spreading other air born particles. Air filters are good at cutting these back, but not if you blow them all over the place.

 

[3dDream]

I did an experiment with a 200 cfm fan blowing on my plants. I did not notice any benefit either.

 

[LolaGal]

i just hope some newbies don't see this thread and think it is OK to leave the fans out of their grow... It's not OK! Must have fans newbies!