Hardening-off, a new techique

digit(ID/WA)May 5, 2013

I recently learned that some horticulturalists advise, and ~ maybe ~ some commercial greenhouses practice, hardening-off of plant starts. How might that be done in a greenhouse? Well, it all seems to be a temperature thing.

You can imagine that a greenhouse with its furnace and air-conditioning, has pretty good control of the interior temperature. It may be run at a range of between 60o and 80o during a normal 24 hours. Turning things down to 45o and 65o may be easy enough during early spring. The plants are then off to the retailers where they will often be sold and kept outdoors.

I don't have "pretty good control" of much of anything. I do try to maintain my heated greenhouse at 60o to 80o but this year moved plants from the steadily filling greenhouse to the new shed-attached hoop house. The little 800w heater in there could keep things about 12o warmer than outdoors, overnight. If it was 27o outdoors, it was 39o in the hoop house . . !

That happened once. The little heater was capable to keeping the interior warm to above 40o other nights. I was happy enuf with that altho' I checked the remote thermometer every morning, well before sunrise. There is now a bigger heater here in the house that can sub for the 800w out there

Many of those plants went on to unheated protection under plastic in the yard. Some things are now out in the open during the days. Some of the cold hearty plants are already out in the garden. Hardening-off has been so much easier this year!

Shade is important, protecting the plants from the wind is important but pulling them out into the open anytime it is above 45o isn't worrisome. I should have set up some simple shelter with a dinky heater years ago!


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david52 Zone 6

Ah, Steve, you're thinking like I'm thinking - but I'm thinking more about heat and drying winds than cooler temps.

These last three years, I've been moving my tomato plants from shade-clothed greenhouse, where the humidity is 80-90%, temps are mid-80's, and maybe a slight breeze, out directly to the garden. And these last three years, within a week along come 20-30 mph winds, with the 85F temps, but with only 5% humidity. The plants just can't soak up enough moisture from the ground to compensate, and the plants never recover - stunted the rest of the summer. I'd thought maybe it was that old virus coming in early off the desert, but now I'm thinking more that its just the dry wind.

So this year, I'm going to put them out on the east-facing front porch of the house - so they'll get strong morning sun, bit of a breeze to sturdy them up, and most importantly, be out in the dry air for 10 or so days before I plant them out.

Peppers don't seem to be that bad. They go outside, face the same dryness and wind, the leaves get all wilty, but they recover.

This post was edited by david52 on Sun, May 5, 13 at 12:13

    Bookmark   May 5, 2013 at 12:11PM
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Some of these things are made tender by a spoiled life indoors. Hot house plants. They cannot handle much of anything - certainly nothing extreme.

The eggplant has been the same route: 1) south window, 2) heated greenhouse, 3) somewhat heated hoop house, 4) unheated hoop house.

Today, I brought the eggplant out and sat them where they were only in the sun about an hour and then spent the day in the shade. It was breezy but above 70o during the afternoon. The leaves curled a little but not like in other years. Eggplants are such pansies!

It has been much easier on the plants this year to go from the 60o overnights; to the 45o overnights; to the semi-shaded daytime outdoors.


    Bookmark   May 5, 2013 at 11:13PM
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