"Janet Baraclough" wrote in message
...
The message .com
from "Gardening_Convert" contains these words:

I would just like to understand why we are always told to harden plants
off over 2 weeks.

We have put plants out without or with very minimal hardening off after
being in the conservatory and they have been fine

Some half-hardy or perennial seedlings need very little hardening
off, especially if they are natives or were started under unheated glass
and experienced chilly nights. Peas and brassicas are pretty tough for
example. But tender, exotic annual plants (like tomatoes) will collapse
or change leaf colour and just stop growing if they are planted out
too soft without careful hardening. Such short-term, tender seasonal
plants don't live long enough to recover properly from an early
setback.

To my thinking the two-week hardening off period is that last two
weeks on the calendar when a frost *might * happen (or not). You can
start putting tender plants out in the day two weeks before the last
frost date, but it would be foolhardy to plant out very vulnerable
tomatoes or courgettes when there's any chance at all of frost.

Janet.
If a plant can grow in warm still conditions, some plants as Janet has said
will set about growing up without investing in the strength structures and
cell wall thickness, when you suddenly expose them to real life they can't
cope, by doing it gradually they get the message and put some effort into
being able to survive wind and cold. I am sure there are scientific words
for all that!

--
Charlie, gardening in Cornwall.
http://www.roselandhouse.co.uk
Holders of National Plant Collection of Clematis viticella (cvs)