Re: Hardening off

**D* G* <g*@gmail.com>**

When I ran my nursery, I had 20K square feet of annual production and we'd
do a 10-15 F DIF program with them.  In other words to hold them at a
salable height and slow growth, I'd start running the ventilation fans
around 5:30 - 6 in the morning to drop the temperature down 10-15F from the
night time temps.  I'd try to hold that temperature as long as possible
until sundown when I'd let the night temperatures go higher than the day
ones.  The "DIF ferential" temperature between night and day was a
determining factor for plant height but the cold temps also hardened off the
plants quite nicely.  That thermal shock and sustained low day temps did
several physiological things to the plants - one of which was to harden them
off.

You can tell the tomato and pepper plants that don't get hardened off
properly - they have an interesting silver sheen to the leaves and a reduced
plant yield.  We used to treat our commercial tomatoes this way for a few
growers and in their ongoing tests to find a replacement grower our tomatoes
always had the highest and earliest yields because of temperature controls
(we were also the most expensive - if I have to get up at 5:30, somebody had
to pay for it) :-)   But we never lost them as customers simply because of
the hardening off (and a few other things we'd do to boost performance and
plant health) our competitors didn't do.  Those extra early crops more than
paid the difference.

So imho, hardening off is not strictly necessary but you can change the
performance of the plant by doing it properly.

On Tue, Aug 16, 2011 at 10:34 PM, Peter Garnham <editor@hamptons.com> wrote:

> I start thousands of seedlings indoors under lights, then harden them off
> in
> a small plastic-covered hoophouse. I drape 50 percent shade cloth over the
> top of the house, ventilate it in warm temperatures and close it up at
> night
> o
>

-- 

Doug Green
Editor-in-Chief, SGF Publishing
One million readers a month can't all be wrong
http://www.douggreensgarden.com/about.html <http://www.simplegiftsfarm.com>
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