Martin,
We have a 20x36 hoophouse near Kansas City, Missouri that is divided lengthwise down the center by a partition made of clear roofing panels. It runs East to West and the South side is heated with an outside wood furnace that kicks on at 50 degrees F. We added a dropped plastic ceiling to both sides last winter as well as an inside layer of plastic all around the sides and ends.
Enough heat radiated from the heated South side to keep the unheated North side from going below 30 degrees about eighteen inches off the floor where the elevated trees sat in tubs. The three large ones were about four feet taller than the soil level in the pots. They were purchased in the fall of 2005 and Spring of 2006.
These larger trees did fine last winter and also the previous winter. I had some die back from small trees I bought from Jon last fall when they started growing early and then we had temps. in the teens. Hollier and Unknown Pastilliere both suffered greatly and I was concerned I might lose them, but after a double dose of fertilizer as recommended by Jon in a post or two, they have both taken off and are now about three feet tall. Hollier is a single stem and Un. Pastilliere has about six long branches. I am trying to decide whether to cut the Pastilliere back or just let it go. It is quite space consuming with limbs going so many directions.
I was told that each layer of plastic provides the added protection equivalent to one zone. We are zone 5b (-10 to -15 F) and gain two zones inside the hoophouse because we have a layer of poly over the top of the hoop (12ft) and a dropped ceiling that is seven feet high. That is equivalent to Northern Arkansas. With radiant heat from the South side moderating the North side where the trees are, it performed more like a 9b zone. Also, the large hoop affords more area for heat absorption than smaller ones. The 9x16 (6 ft. tall) hoops we used to have were the same temp. inside as it was outside except when the sun was shinning. The greatest benefit at night with them was the wind protection, which was substantial. Idential crops outside were killed when those inside were fine. Didn't have figs then, just veggies. I do not know how a fig tree would do in a small greenhouse that really heated up during the day and then dropped substantially at night.
This year, fruiting is later than last year because we had a lot of very cold temps. after an earlier warm up. Everything is at least two weeks later outside the hoop and inside was no different. This year I picked the first breba Italian Honey on June 11. It was a little green tasting, and mildly sweet. The next one was just shy of 2 oz. but dry and not good at all. The next one was left to soften and was sweet and fairly tasty as was the rest of the breba crop. However, last years' breba crop was much better. This years main crop started about the middle of July and it has a more coarse texture with lots of crunchy seeds. It has to be absolutely soft to be good and they are splotched with brown when ripe. That didn't happen last year. Last years' main crop was much better tasting also.
Aug. 3, I picked the first Violette de Bordeaux. It had a breba crop that was tasteless and so I removed all of them. This main crop fig was good; sweet, with a lot of texture. The first main Hardy Chicago was picked August 5 and was similar to the VdB. I prefer the Italian Honey over the dark ones despite the ugly brown splotches covering most of each fruit.
With the early ripening of figs in the hoop, they also finish earlier. Others were picking ripe figs for weeks after mine in the hoop were done last year. I fully intended to plant the three larger trees in the ground in the hoop this Spring but the unusual weather and other factors kept that from occurring. My new goal is to have them in ground shortly after all the figs are done ripening. In-ground figs should have more growth and thus more figs - a very good thing to have.
Elizabeth