Temperate Fruit & Orchards > Temperate Fruit Discussion

Zone Pushing - What to grow in unheated greenhouse in 8a

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Nick C:

--- Quote from: All the fruit on June 09, 2024, 03:48:19 AM ---
--- Quote from: Nick C on June 08, 2024, 12:07:03 PM ---You'd be good with hardy tamarillo for sure. I have one in ground under a poly tunnel in 7a

--- End quote ---

No heating? Also where in zone 7a?

--- End quote ---

Just some frost cloth and black garbage can filled with water, no heating. I'm in New Jersey

Plantinyum:

--- Quote from: drymifolia on June 06, 2024, 05:19:41 PM ---
--- Quote from: All the fruit on June 06, 2024, 01:50:54 PM ---How much does such a greenhouse help?Is it like 8b or even 9b?

--- End quote ---

Unfortunately, if you aren't heating it at all then it provides very little protection against overnight low temperatures, but the best way to know for sure is to install temperature sensors inside and outside, and compare them just before dawn.

You will likely find that by the end of the night, the greenhouse is (at best) one or two degrees warmer than the outside temperature.

During the day, it can be dozens of degrees warmer, but once the sun is gone, the extra trapped heat will generally all escape within a few hours.

As an example, here's the ∆°C chart (i.e., how much warmer it is compared to the outside) for my greenhouse today since midnight (currently just after 2pm in my time zone). Overnight it was about 2°C warmer, and has about 150 watts of seedling heating pads and about 100 watts of LED grow lights currently turned on. It would be about half that otherwise.



The 8am anomaly is due to the morning sun hitting the outdoor sensor on the outside north wall of the greenhouse and creating a false reading a few degrees warmer than the air temperature. The sudden drop before 11am was the exhaust fan turning on, and that's still running now. Without that, it would probably be 25+ degrees warmer inside (and my plants would be cooked).

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Wright after i build mine, i monitored the temperature differences between inside and outside, trough the first winter, before i planted my tropicals. The result was that i had a stable 4 degree C positive difference on the inside. Sometimes it was les, sometimes it was more, but 90% of the time the difference was 4 degrees. Thats without heating, and now after it is heated, the gh equals to zone 10- 11, and i am in zone 7.
For a passive greenhouse, the place and how it is build is also important, mine had such a high temp difference, becouse it is on the south side of a building, also i have solid concreete surounding base.


--- Quote from: All the fruit on June 06, 2024, 01:50:54 PM ---Hi everybody,

my friends have a huge greenhose (about 20 000 sq feet) every hobby gardeners dream. Single glass, on an open field near Heidelberg/Germany (teaditionally USDA zone 7b, now 8a. They like exotic fruits and with a little help from me they are starting a non herdy fruit collection. We already have Musa vasjoo, sikkimensis, Musella lasiocarpa, Ensete maurelii, Yuzu, Ichang Papeda, some surviving citrus rootstocks and seedlings, pomegrenades...Wondering if strawberry guava, mountain papaya or hardy tamarillo will grow there

My questions:1:  What else can we grow there? Im especially interested in the super rare and tasty fruits
2: How much does such a greenhouse help?Is it like 8b or even 9b?
3: Any specific care tips for those plants in such a place

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i suggest you to monitor the environment for a winter, just to know what your lowest temperatures are, meanwhile you can plant the more hardy stuff. Mountain papaya is supposedly hardier than regular papaya, i have 3 that are doing wonderful and also setting fruit atm. But i also have 5 regular ones, both are grown in the same greenhouse, i cannot tell you how much hardier mauntain papaya are, as i keep the gh very warm trough winter as i have tender stuff, like the regular papaya.

drymifolia:

--- Quote from: Plantinyum on June 10, 2024, 03:31:31 AM ---For a passive greenhouse, the place and how it is build is also important, mine had such a high temp difference, becouse it is on the south side of a building, also i have solid concreete surounding base.

--- End quote ---

I don't think the concrete base helps much, concrete and soil have similar heat-retaining capacity. Being attached to a (presumably) heated building is why yours maintains such an unusually high ∆ vs outside. Even before you added heat inside, your greenhouse is heated, by the waste heat escaping from that building.

The OP already said this:

--- Quote from: All the fruit on June 06, 2024, 01:50:54 PM ---a huge greenhose (about 20 000 sq feet) every hobby gardeners dream. Single glass, on an open field near Heidelberg/Germany (teaditionally USDA zone 7b, now 8a.

--- End quote ---

Single pane glass in an open field probably has an R value low enough that it reaches equilibrium with the outside temperature within an hour or so, but maybe it lags the outside low by that much time, so it might be about a degree (Celsius) warmer at dawn, if the outside temperature is continuously falling until dawn. If the outside temperature goes flat, the greenhouse will probably match it to within a fraction of a degree.

But I agree, sensors will answer the question quickly. To give a better example than the one I posted above, here's a pretty typical stretch of winter days here in Seattle, in my detached greenhouse that has twin wall 8mm polycarbonate glazing (a much better R value than single pane glass):





The first day was thin clouds, the next day was partly sunny, then it rained for a few days and you can see on those days with very little sun, the ∆ falls to zero.

All the fruit:
Pity. I thought a greenhouse of any kind would make much more difference. But i hope they can increase the effect by keeping the inside dryer in winter and do a lot of passive heat retention and insulation.

Where near Sofia do you live. During my childhood in Sofia such exotic plants would have been impossible to obtain.

drymifolia:

--- Quote from: All the fruit on June 13, 2024, 12:39:05 PM ---Pity. I thought a greenhouse of any kind would make much more difference. But i hope they can increase the effect by keeping the inside dryer in winter and do a lot of passive heat retention and insulation.

--- End quote ---

Is there no way to add heat? A wood stove to use during unusually cold weather, at least? That's a very large greenhouse to heat with electric heaters, so even if you have electrical hookups that would likely be too expensive.

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