Your internodal stretch is caused by the far red of the light spectrum which also is high towards the end of the day. What you are describing of lowering your temperatures in early morning must be a rapid drop in order to accomplish what you are saying. There is also differences in difs....positive difs and negative difs...one is higher night temps and lower day. The other is what actually promotes internodal stretch. Hope this gives you some information, you can also reduce growth with water temperature.

I've been following this temperature difference/internodal stretching dicussion for a while on another thread. Interesting. But I can't help but wonder how the plants manage in places where these temp differentials are a natural occurrence. For example, out in Arizona there are huge day/night temperature differentials. Native plants may have adapted to it, and there are folks who appreciate those plants (thank goodness), but there are others who just must have their old favorites from back home.

Di

Growin,

I haven't noticed that I have excessive stretch, but I may have inadvertently managed it with a low DIF and a temp reduction around dawn without knowing what I was doing. My temp swings may approach 30*F, but I have heard of people with 50*F or more. The few references I have seen regarding lowering the morning temp don't mention anything about the speed of the temperature drop... any references? And is kicking on your exhaust fan (in the warmer months) at 5am generally rapid enough?

Negative DIF possible in the cooler months, but not practical for most of us... seems like mostly a research tool.

SB

SB can you link some of your data? As you know I love to talk about this subject. One other reason plants stretch in a g/h environment is simply they are to close together and don't have adequate growing space. It's a real problem for one who try's to grow too much stock in one space. (personal experience from our 1st year:)
Ideally maintaining a constant temp is the best solution.
Currently we come close. 55 at night and aim for 60 during the day, although 65ish does happen. As spring approaches we will get higher temps during the day. Shade cloth goes on then almost every thing comes out of the g/h and goes outside.

Some plants seem to be more suited to stretch then others.
Delphiniums will stretch while primulas tend not to.

agardenstateof_mind
Most plants in the natural world tend to have adequate growing space. There is always the plant that does better and crowds out the less mature plants surrounding. Survival of the fittest after all. Although looking at a dense forest some trees will grow taller and stretch to receive the most sunlight. Stretching does happen in nature too.

Hi Mylu, how've you been?

This link describing hourly growth rates and cold treatment, interesting reading:

http://www.for.gov.bc.ca/nursery/fnabc/Proceedings/TempAndIntegratedControl.htm

This one below has a chart of the "DIF sensitivities" of different plants. It describes a regimen involving a 8*F drop for 2 hours 30 minutes before dawn.

I'd like to hear your thoughts.

Any hobbyists doing this?

Here is a link that might be useful: Plant DIF sensitivities

SB,

From my experience and education I have seen that the difs should not be more then 10C. You are also creating some potential mildew situations with this dramatic temp difference. The condensation factor will promotes mildew since it prefers swings in humidity. During the summer months internodal stretch is reduce due to daylenght and the amount of dusk dawn being signifcantly less part of the daylight hours. Drawing your fan on in early morning may assist. But top venting allows for cooler air to fall and "hammer" the plants. This hammering only occurs for about 15 minutes and then the temperature is allowed to climb through the morning naturally. What is the crop you are growing?

Hi thegrower,

I don't have a crop per se. I am but a lowly hobbyist. I grow a little of everything, including peppers, toms, lettuce, herbs, but really my GH is turning into a collection of subtropical/tropical plants... Musa, citrus, guava, Heliconias, that sort of thing.

I'm interested in the internodal stretch issue growing plants like Jasminum polyanthum and broccoli. I had a terrible time with broccoli; in fact, I finally tossed them (interestingly, they are 3 out of 3 in DIF sensitivity in that second reference above). My DIF generally doesn't go over 20*F, what's that, about 11C. DIF not as important with woodies, I would guess.

My controller comes preprogramed with the DIF from 6-9am. The example in the manual shows DAY setting at 70F (21C), a NITE setting of 65F (18.3C) and a DIF setting of 50F (10C). All are adjustable, of course, but does that sound about right? That temp drop is greater that the 8-10*F drop cited in the study above.

Thanks. Stressbaby