Internodal stretch and your GH temp

One topic I have not seen discussed on the forum is the issue of internodal growth and "stretch".

Usually we try to limit internodal stretch. Plants with greater internodal stretch are lanky and floppy. One of the main factors affecting internodal stretch is daily temperature variations in the GH, the difference between the day temp and the night temp, sometimes called DIF. The greater the DIF, the more internodal stretching occurs. Internodal stretch is lowest when the DIF is negative, meaning night temps are higher than day temps...really not practical for most of us...but by limiting the difference and keeping night and day temps closer together, you can limit the stretch and you won't have floppy, lanky plants.

How do you do this? Most important is the thermostatic control of heat, ventilation, and cooling. But adding thermal mass will blunt the temperature swings in the GH. During the day, heat will be absorbed by the barrels of water, and this heat will be released at night.

What are your thermostat settings? Have you noticed differences in plant stretch in relation to day/night temp swings?

SB

I should mention that while this phenomenon is generally observed, there are differences in how certain plant species might respond.

Oh, and I forgot the coolest thing...

There is another way to limit internodal stretch, and that is to drop the temp for a couple of hours right at dawn. A 2-4 hour cool treatment limits the plants' early morning growth spurt.

In warmer weather, this isn't hard to do at all. Set your ventilation or exhaust system to run from, say, 5am to 8pm, drawing in the cooler morning air. A greenhouse controller makes this very easy. Some have an option for early morning DIF settings in addition to day and night settings.

Has anyone else tried this? SB

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

For those interested, this link gives the response of different plants to DIF.

http://www.ces.ncsu.edu/depts/hort/hil/hil-528.html

Nobody has floppy broccoli or basil?

I think that this year my summer settings will be something like 80*F day, 75*F night.

Ridge vent: +1
Intake shutters: +3
Exhaust fan: +6
Misting: +10

I'll try dropping to 65*F from 5-8am, so the exhaust fan kicks on at 71*F.

SB

What plants are you having a problem with internodal stretching? The article lists several contributing factors.

jb

JB from GW!

I'm not having a lot of trouble... maybe my Jasminum polyantum is a little stretchier than I would like... on another thread here at DG someone remarked that their temps were bouncing from something like the mid 30s to over 90 every day and I just brought it up to see if anyone wanted to discuss. I didn't get many takers... Dmail...

SB

I have only had my greenhouse since Fall and don't have much growing in it right now, but I have heard about internodal stretching and it is a problem for commercial growers. If I had a crop in their right now. I to would have wild swings as there is no heat and the last few days have been sunny and the nights below freezing. Of course by the time I am growing a crop I'll have a heater and a vent system and will hopefully be able to work with plants that are having a problem. I am also thinkign that since most of what I will grow will be perenials, shrubs, vines and trees I amy not have as much of a problem. Seems the annuals and fast growers are more of an issue.

jb

This message was edited May 28, 2010 4:54 PM