Temperature Fluctuations in "Cold House"

rzeles

All,

I live in NJ-Zone 6B I believe, and recently purchased the SpringHouse™ Portable Greenhouse Kits to overwinter my pines and maples.

I also purchased one of those remote electronic thermometers at Lowe's for $12 that enables me to remotely monitor the temperature in the greenhouse from inside the house (quite cool).

Although I am keeping the front and back windows open on the greenhouse, the temperatures greatly fluctuate from 29 F to 60+F. I think this is primarily because it is facing South, however, I have no other spot in which to place it.

The question is, will this constant freezing and thawing kill the plants. I am not concerned about the pines as much as the Trident and Jap Maples.

I thought I saw something indicating the thawing and freezing is not a good thing.

I will browse through the posts again, however, any expert thought on this. If I have to move them all to a shed or garage I will, but, this will be a pain.

Thanks.
Ron

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Candy_J_Shirey

Ron -

I also have a "cool" greenhouse (in zone 5B), and struggled with the temperature adjustments for a few years. My greenhouse also faces south but it does not have the fluctuations that you record. My greenhouse is a permanent one with much of it (the bottom 4-6 feet) underground. It is heated with natural gas and stays at 35F +/-3F from December to March.

In the past, I have kept it at 45F and had tridemts and Japanese maples leafing out in the beginning of February. Also lost a couple of nice white pines, because (I suspect) it did not have the dormancy that it needed.

It is my understanding that the freeze/thaw cycles are not dangerous by themselves but the danger lies in your temperatures not allowing a complete dormancy for your trees.

-Candy

cray13

I have one of those remote thermometers as well and have noticed that they are not always accurate. If the temperature unit outside in your cold house is placed in a location where it will get direct sunlight it can report greatly exaggerated high temperatures. I discovered that placing the unit under a shelf or otherwise keeping it shaded from sunlight gives a much better reading.

Just thought I'd share my experience. Your temperature fluctuations may not be as bad as you think.

Dav4

Personally, I would try to reduce the daily warm-up, if possible. Is there a way to reduce the heat gain by blocking some of the sunlight from entering the greenhouse...maybe by using burlap or something similar? I'd try to keep the daily highs at 45F or less.


Dave

Candy_J_Shirey

Dave -

Have you ever overwintered pines and maples at 45F? If so, what was your experience?

In my experience, this is not cool enough to enduce a good dormancy in white (or red) pine or Japanese or trident maples. My pines did not survive. The maples came out of dormancy in early February and were weakened.

-Candy

Dav4

45F isn't the temp I reccomend to overwinter trees; it's the upper limit of what I think they should be exposed to during dormancy. I've overwintered tridents, white pines, black pines, junipers and an assortment of Acer palmatum cultivars in my unattached garage. My goal has been to keep the temps in the 30s F or lower from December until the end of March...easier said then done. I've found that once the day temps consistently pass 45F and the trees have met their dormancy requirements, the maples start to wake up first, followed by the others. Also, no problems meeting dormancy requirements here.

Dave

rzeles

All,

Thanks for the replies. All good thoughts.

We are having very mind weather the last week or so in NJ, (50's during the day), thus, I hope this will be the anomaly.

I put a brown tarp over the top in an effort to create some shade. (common knowledge would assume a dark tarp will actually attract heat, we'll see).

I actually moved some of the pines to a bench with a plastic sheet as I do not want to take a chance. Moved some of the maples into my unheated garage. Temps are in the 40's the last few days in the garage.

Let's hope for some cold weather!

Thanks.
Ron

rockm

You are finding why overwintering a a greenhouse--even an unheated one--isn't the best way to handle hardy temperate trees. At 45 degrees, or higher, plants are in danger of breaking new growth and a number of fungal and disease problems.

At any rate, the fluctuating temperatures even 30-63 are far to warm to overwinter pines and/or maples. Pines and maples should be more than OK in your area outside with only mulch and a windbreak.

Greenhouses trap heat and that's NOT what overwintering is all about. Overwintering is about keeping an evenly cold--but not too cold ---above 20 but below freezing--usually does the trick--temperature at the root zone of the plant.

Greenhouses are simply too efficient at trapping heat in areas above Zone 6 (or so) for even "cold" greenhouse overwintering.

Placing a tarp of ANY color over the greenhouse will reduce the heat inside, as greenhouses have to trap heat to conserve it. If it doesn't get through the glass, it isn't trapped. Any radiational heat from a dark colored tarp will be of little consequnence inside the structure.

I'd just move the pines outside, mulch them, let them be. The maples might also be moved to a sheltered spot in the yard and mulched in. MAKE SURE THEY ARE OUT OF ANY DIRECT SUN. DIRECT SUN IS THE ENEMY OF OVERWINTERING PLANTS.

I'd save the greenhouse for tenderer species like pomegranate, serissa, etc.