"Staycalm" wrote in message
u...
I was just wondering is there anyone who is able to grow tomatoes in a cool
climate nearly all year?

I don't have experience in full-size greenhouses just cloches and little ones
for seed raising but I am looking at a bigger one for exactly the reason you
are. Take this as 30% practical and 70% theory. Corrections are welcome.

You get several benefits from a greenhouse, warmth so you can grow warm season
plants in not warm seasons, some frost protection, sun control and maybe
humidity and pest control.

The first is pretty obvious, you have a warm air trap, the radiant heat of the
sun goes in and most stays in, they don't call it the greenhouse effect for
nothing (duh!).

The second doesn't work as well as you might think 'cause the clear panels
radiate heat out on cold clear nights just like they take it in during the
day. To get over this you will have to blanket at night and uncover during
the day which is some work. Or you can add tubs of water to increase thermal
mass. The water takes in heat through the day and gives it out at night, I
can grow frost sensitive plants near my concrete verandah or water tanks using
this system, as both have good thermal mass.

The third also involves blanketing or painting with whitewash that can be
washed off later. In the winter this is not an issue for sunloving plants
like tomatos but in the summer you can get sunscald or overheating with a
clear covering.

Which brings us to one of the big drawbacks. Many plants that didn't come
from tropical jungles don't like heat and high humidity, they get fungal
diseases very eaily if you don't have air circulation. Most of my tomatoes
turned to crap this year because of the wet summer. That's what you have in a
closed greenhouse, a big fungus cooker. You need air circulation and some way
to control it (windows etc) and the time and energy to do the controlling.

You would think that you could keep insects out but this isn't as easy as it
sounds and in some cases (eg aphids) they will go crazy in a few days due to
the ideal conditions of warmth and humidty. This leads greenhouse people to
spray for fungi and insects.

I went to the space-age giant greenhouse at the local tech college where they
teach horticulture. This thing has electric windows, fans, water sprays, and
automatic ice-cold beer. It's all controlled by a computer via analog/digital
interfaces to the equipment and to thermometers and other sensors. Very
geeky! But there was very little growing in it. I asked the teacher why not
and he explained they were having software problems and it kept killing
everything.

How hard would it be to have a greenhouse of some sort over the garden bed?


Not terribly hard. Hoops of 40-50mm polypipe anchored on iron water pipe
driven into the ground. Some bracing. Your cover of choice over the top.
This is the tricky part. Clear plastic film needs to be fastened so that when
the wind blows it doesn't tear. And even UV stabilized it only lasts a few
years. Unstabilized maybe only a year or two. There are fabrics that are
semi-transparent that are tougher but you don't get full sun. Rigid plastic
sheet and glass last much longer mostly (how about a nice hailstorm) but are
very expensive and need a much stronger and more rigid frame which compounds
the cost.

My idea is to start small and experiment under my local conditions before I
spend too much. I would love to have warm season veges all year round and
reduce reliance on the supermarket but I am prepared to punt it if it's too
hard or requires too many chemicals. Those who have been down this track tell
us all about it.

David