temperature DIF day/night to control stretch

[Nicol Bolas]

So the general rule with most plants is that the higher the nightime temperature compared to the day the shorter your internodes shall be. So like 73 day/65 night with give stretchy plants while 73 day/70 night will give shorter plants and 73 day/76 night shortest of all. This work with tomatoes. does it work with weed? If so it would be a great way for me to help with the lanky sativas i'd like to be growing.

 

[magiccannabus]

Higher or lower doesn't matter as much as the actual difference. So plants that have a 20 degree day/night difference will stretch more than those that have a 10 degree day/night difference.

 

[Nicol Bolas]

exactly
smaller temperature difference = shorter internodes = more efficient use of light penetration = higher yields!
for tall strains at least
Why have I never seen anyone on these boards mention this? Is it too impractical?

 

[inefectualize]

where are you getting your information from? I posted about this a few months ago...here are some quotes

kind of along the lines i was thinking....this is just the abstract, but it talks about the optimal temp drops to shorten internode spacing without impacting vegetative mass...

http://www.ingentaconnect.com/conte...33?crawler=true

this next article talks about the importance in nighttime drops in its role in the transportation of sugars through the plant and how you can maximize harvestable plant matter....pretty interesting stuff...

http://www.crophouse.co.nz/files/Gr...owth_-_view.pdf

I have experience with some very picky high elevation plant species which will quickly die without substantial night-time drops

this quote
Despite the fact that in general there was more growth occurring at night than during the day, our attention was drawn to one particular characteristic of the daytime SER pattern. The peak which occurred at the start of the day period under constant, and positive DIF conditions accounted for up to 20% of the total daytime growth. We reasoned that elimination of that burst of growth at the night/day transition (or dawn in the natural world) could have a significant effect on the total daily amount of stem elongation. Since the growth peak seemed to be enhanced at higher daytime temperatures (and reduced when day temperature dropped) we decided to look at the effects of dropping temperature for various periods at the start of the day.

Choosing our standard 18.3C regime we dropped the air temperature around the plants to 8.3C for either 2,4 or 6 hours beginning immediately at the lights on event (Figure 5). The results were startling. SER dropped rather than increased in the early part of the day but the decline in growth rate did not last until the end of the pulse. It seemed rather that the low temperature shock induced a timing mechanism which temporarily suppressed growth. If cool conditions persisted, the timer was reset so that the growth suppressing effect continued.

Overall the effect of the low temperature pulse was to significantly reduce daily growth. The effects of the low temperature pulses were, however, transitory and had no effect on the overall periodicity of the rhythm indicating once again the very strong relationship between environmental cues and the underlying endogenous rhythm. The cues of light and darkness are of paramount importance. 4 and 6 hour pulses, as we might expect, tended to be more effective than those given for shorter time periods but 2 hours at lower temperature at the start of the day was quite effective in reducing daily stem elongation.

Low temperature pulses given later in the day also reduced stem elongation, but because they did not coincide with the early growth peak they were less effective in limiting stem elongation. This raises the question of when and how temperature drops should be timed to effectively control stem growth.

While temperature pulses or the imposition of day-long low temperature (i.e. negative DIF conditions) are less effective if the low temperature does not start at the beginning of the day period, some useful work in Scandinavia has established that temperature can be dropped before dawn (or a lights on event) and still retain the effectiveness of the negative DIF treatment (Table 2)

Is from here

http://www.for.gov.bc.ca/nursery/fn...atedControl.htm

this next quote is from the same source and talks about the potential role of the interaction of far red wavelength (sunrise) with temperature drops....

In recent months we have conducted several experiments under controlled conditions in greenhouses under natural lighting. The early day growth peaks which may play such an important part in the overall daily stem elongation response in several species seem to be initiated by early morning (pre-dawn) lighting when the spectral balance is shifted to the far-red end of the spectrum (Figure 8). We are now investigating the possibility that temperature interacts with this spectral shift in influencing the elongation response.

The control of temperature and more specifically the DIF technique is clearly a powerful production tool but is it sufficient to produce the carefully graded plants which are the mainstay of the horticulture and forestry industries? In some cases environmental manipulation may be all that is necessary, but increasingly we are looking at DIF as a component in an integrated approach to plant growth control. Chemical growth regulators are used extensively in horticulture and have for many years been the method of choice for controlling excessive stem elongation. When these chemicals are used in combination with DIF, we have found that although the growth regulator effect predominates, DIF still acts and in a manner which appears to be quite independent of the effect of the growth regulator. Chemical growth regulators primarily affect the synthesis of gibberellic acid in the plant. When that synthesis is blocked stem elongation growth is suppressed. It appears from our most recent work that DIF does not affect gibberellin synthesis, although it may very well affect plant sensitivity to gibberellin. In practical terms this means that DIF can be

used in combination with growth regulators in an integrated way to limit stem elongation. This is especially relevant when we consider the mode of action of the new generation of chemical growth regulators (the triazoles) now under trial and consideration for registration. This is because plants are dose-sensitive to these chemicals and the quantity of active ingredient applied to the crop can be varied to provide a graded control of elongation. If DIF is used as the fundamental elongation control strategy, then growth regulators can be used to "top-up" the response as required.

Above all stem elongation control and the ultimate size and stature of plants is not something which, as producers, we can assure with a single treatment (whether that is an application of a chemical growth regulator or an adjustment of temperature). Rather it is an ongoing process of assessment and action which requires careful record keeping, but record keeping of a very specialized kind. In the greenhouse industry the techniques has become known as graphical tracking. To apply it we simply need to monitor crop growth at intervals and determine the definable, low resolution pattern of stem elongation during the production cycle (Figure 9). With this information we can construct a graph to represent the long-term pattern of elongation, and modify it to represent the desired response. During crop production representative plants can be monitored and DIF and/or growth regulators used to give the desired growth trace.

just a couple more quotes

Most flowering plants prefer the same daytime temperature range, but grow best when nighttime temperatures range from 55 degrees to 60 degrees F. Lower nighttime temperatures help the plant: recover from moisture loss, intensify flower color and prolong flower life.

I think this paper is probably where this info came from...

http://www.jstor.org/pss/2437636

and a quote from the paper....

The rate of stem elongation and the setting of fruit of tomato plants, grown in gravel and watered with nutrient solution, is very uniform from plant to plant, from week to week, from season to season, and from year to year, provided they are subjected to the same temperatures. The rate of stem elongation is a sensitive indicator of the effects of different temperatures on the plants, and changes immediately upon change of temperature. The growth rate is not dependent upon the humidity of the air, inasmuch as a decrease in humidity causes merely a temporary decrease, an increase of the relative humidity increases the growth rate only temporarily. When tomato plants are grown in a constant temperature twenty-four hours per day, the optimal temperature lies well above 20⚬C. At 26.5⚬C. a steady growth rate of 23 mm./day is reached when the plants are 30 cm. tall, which rate is maintained as long as the plants are kept trimmed to one stem. Plants grown at lower temperatures have consistently lower growth rates. But plants kept warm during the day (26.5⚬) and cool during the night (17-20⚬) grow more rapidly than any of the other groups (27 mm./day). The lower temperature is only effective when maintained during the dark period. Approximately the same temperature relation holds for fruit development. Fruit set is abundant only when the night temperatures are between 15 and 20⚬; with lower and higher temperatures during the night, fruiting is reduced in amount, or even absent. Artificial light when applied during the cool night period completely inhibits fruit formation. The conclusion is reached that thermoperiodicity in tomatoes is due to the predominance of two different processes at day and at night, of which the dark process has a much lower temperature optimum than the light process. From other work which is discussed, it is suggested that thermoperiodicity is a general phenomenon in higher plants.

 

[magiccannabus]

Interesting, I will study that some. My plants have always seemed to love constant temps, but I'll do some experiments when I get my system going again.

 

[riverrat]

I am seeing this first hand with my current grow, I recently set up this grow and have just now got my temps under control. During first month of flower my daylight vs night temps were on the order of 25 to 30 degrees. I have lots of stretch and long internodes on this grow that I did not have with the same strain on my previous grow where the temp diff was on the order of 10 degrees or so.

RR