In the winter time the north wall gets absolutely NO sunlight. You can make that wall an insulated wood frame wall. My GH's insulated wood frame wall is my house and it actually provide minimal heat. If you use quadruple layer glazing on the roof, east and west walls as I did you can expect a 40 to 60 temperature rise in full sun at solar noon. Heat rises and you need the extra gazing to perform well. The east and west walls get so little sunlight that you either need the 4 layers glazing or an insulated wood frame wall. Since your GH will be needed at equinox we make it quadruple glaze. My front wall will be 3 layer.

As far north as you are it will cost less to bring your plants inside and set them in the corner of your basement and enclose the two open sides and use CFL's, or use a box as in my setup below. It uses 12 CFL' at 18 watts and can hold 16 trees in 5 gallon bucket. It worked extremely well. The beets on the ground floor heated up the citrus tree's roots to about 80 F and the citrus room ran around 75 F-90 F.

If you heat with oil, electric or propane, You can heat with CFL's at about the same costs. Might as well grow citrus trees in the basement.

I got about $50 in organic beet greens and picked huge beets a month after setting them out in april. It pays

you will need to maintain a rootzone temp of at least 55 degrees to avoid leaf drop when the greenhouse heats up during the day. My greenhouse is a simple hoop house. 10x12, wood sided north and south wall, 6mil plastic. We maintain 60 with a small gas heater. It will easily reach 85 plus on a cold sunny day.

joe At 19F outside temperature on a sunny day my inside temperature reach 78F. You and I can expect some where around to a 60F temperature rise on a clear sunny winter solstice day. The main problem is after sunset. The temp drop fast and we have to keep active growing trees above freezing. My green house has a 4 layer glass roof. 2 layer glass south wall, 4 layer glass west wall, and a 2 layer glass east wall. See pictures

Steve

Thanks! Here's another question, regarding artificial lights:

Whether were talking indoors or in a greenhouse my question is are citrus responsive to/need long nights during the winter in order to properly bloom and set fruit? In other words are they sensitive to photoperiod? If I ran lights for 14 hours a day all winter, would they just think it was summer and refuse to bloom?

14 hours might be a tad much. Now would that stop them from blooming, probably not. My trees just finished their main bloom a few weeks ago in the greenhouse. If you are supplementing indoors I would stay at or below 12. i would try to mimic the conditions the trees would be in if they where growing in florida or somewhere like that. I really boils down to Light and Temperature to make them happy.

Joe

I can't help you with that question on the time under light. All I have up to June 2014 were seed grown citrus. They won't fruit until a leaf node count has been reach. My goal was to make them grow at phenomenal speed till they were to big to handle indoors. After all winter inside they were already to big for me to handle so they went out side. If I were to buy a grafted tree I would get it in late summer and up pot it and grow as I did my other trees. I would not let it flower and I would see If I could complete one more winter under lights. I would have a sizable tree ready to bear a good load of fruit. I inherited 2 Meyer lemon trees that never saw lights under my ownership. The are flowering now and may put on a heavy crop.

I have a poncirus Trifoliata in a 30 gallon container growing absolutely fantastic. I planted it in a mixture of 50% backyard dirt and 50% totally rotted compost. In other words if you have a tree grafted to poncirus you should do well in not perfect conditions. I would still follow the citrus advice on soil until you have a real feel for what the tree needs in water and feed

{{gwi:599903}}
!8 month old PT in 30 gallon container.

{{gwi:569341}}
Sweetlee first planted in ground in 5-1-2014.

Trees grow much better in ground than in containers

Sweetlee 12-12-14 6.5 months later. She is 2 the size of the container sweetlee

Steve

Would most citrus be ok in this situation in a GH in winter?

1. Using heat cables wrapped around the containers and using a thermostat, maintain root temps at or above the mid 60s F
2. Night temps in GH 41-45
3. Daytime temps from the 40s on cold cloudy days, 60F on a more average day, possibly up to 80 on sunny, mild days

My thought is that if the roots are kept at a warm enough temperature the cold nights but warm sunny days will provide for good conditions for good color development in the fruit. And these conditions are not all that dissimilar from the central valley of California, albeit not as sunny.

Yes they should be fine under those conditions. And no citrus do not need long cold nights to set fruit. Stone fruit likes plums, apricots and apples need the chill hours to set fruit but not citrus, they like it as warm as you can keep it.
Evan

I grow my citrus in a hoophouse that I seal up tight and heat in the winter like a greenhouse. The roof is double layer of plastic sheeting but the side walls and end walls are single layer reinforced plastic curtains - so it is not very energy efficient. At first I only tried to keep it above freezing. I'm in zone 7b (Raleigh, NC) and it wasn't too hard, most winter days are in the 50's in the daytime and low 30's at night. Lately we've been having periods of very cold nights - lows in the single digits and daytime highs in the 20's (and cloudy) so it has been a lot more work to keep the plants happy these last couple of years. I heat with wood for the most part (wood is free). I have kerosene and electric heaters for backup or if I need more heat than the wood stove can provide. It's do-able but time consuming (chopping all that wood) and expensive (buying high quality kero or paying the electric bill). No matter what you grow in a greenhouse in the winter, it is an expensive hobby.

In my experience my trees got too big to move in and out in a couple of years. They also got too big to repot easily soon after that. I solved that problem by making what I call 'cage pots' made by circling the tree with a ring of hardware cloth lined with landscape fabric and held together with zip ties. That way I don't have to lift anything to repot them, just snip the zip ties and open up the cage and replace the media. Citrus love the extra drainage. The only problem with this is that the pots are not movable (no bottoms) and they hold around 50 gallons of media each. A side effect of all those large pots of media is that they hold on to a lot of heat (damp media stays warm longer than just about anything). So during the day I let thing heat up as high as they can get in the middle of the winter knowing that the days are short and that after sun set I will have a few hours before things get cold enough to need extra heat. Back when the trees were smaller I would even store large tubs of potting media in the corners to act as heat sinks. Some people do the same sort of thing with large containers of water, but I find that water gives up its heat faster than damp media.

I aim to keep everything around 50 degrees which keeps the roots active. If you want to store the plants at a lower temperature you would want to keep things dryer to avoid rotting the roots.

Keeping the roots warm is probably the most important thing we can do for the trees. My green house drops below 40 often and hits 32 degrees on the liquid side a fair amount times. I use the water reservoir and soil heat sink methods to keep it warm. As John mentioned the soil gives off heat at a slower speed but the water will give off vapor with the heat of vaporization coming from the water and not from your greenhouse air or your container citrus's roots. As the vapor condenses on the glazing it gives off 520 calories of heat per gram. When the water freezes on the glazing it give off another 80 calories of heat. The water turns to ice at exactly 32 degrees and locks the glazing at 32F and the inside can't freeze and your trees are safe. Keeping the roots warm guaranties that the trees will not suffer from a bright sunny day that rarely follows here in Cincinnasti.

On a bright cloudless day I can expect a 60F temperature rise when the sun is at its lowest path December-21-northern hemisphere.

My greenhouse hit 78F on a 19 F day. On a fairly clear day I hit 84F on an outside temp of 31F. If you have the room in length a 32 foot long east to west by 5 foot north to south greenhouse with an insulate north wall is much better than a 16 foot by 10 foot typical all sides glazed greenhouse kits you see at stores. No sun comes though the north wall and a whole lot of heat bleeds out. I do no assist with any heating unless the temperature dropped below 10F till now. Most of my trees are in active growth so I provide heat at night to 50+f to get a real jump in the morning as the sun rises. This way I top 90F often and stay above 80F for hours each sunny day. The trees love it.

Bottom line. keep your roots above 60F keep the greenhouse above freezing. Preheat your air in the morning when a forecast-ed sunny day is to follow. Do so after January or earlier if your tree start really growing well. This will maximize the time your greenhouse is warm with minimum heating costs.

Steve

My biggest problem is that I tend to under water and often get dry out root damage and root rot has never been a problem of mine even though I uses a much heavier soil mix than suggested for citrus. You will have to watch your tendencies.

I just wanted to say my greenhouse at 1:00PM Just top 100F. I"ll keep my window closed to hold in that heat to warm the root bases, This is just 70.71 miles south of Columbus and 70.71 miles east.

Go for it Joe and join the big league-er as seen in the bugs seires of threads. Here's Bugs 12

Here is a link that might be useful: http://forums.gardenweb.com/forums/load/citrus/msg0119455522832.html?21853

Thanks for the help.

Ok, let's talk media and containers.

1. Have you tried Al's 5-1-1 or Gritty mixes (from the container forum) for citrus? Are they good?

2. Do any of you recommend Smart Pots or other fabric or root pruning containers?

Al's mixes are good but not for everyone. The cost involved, finding the materials and mixing it up can be difficult. I tried the gritty mix a long time ago. It became too heavy and costly when i started mixing enough for all my 5-15 gallon pots. At one point I had 45 plumeria and 10 citrus plus many others. It also dried out way too fast in our 105 degree summers. 5.1.1 is good for me but I found a better way than mixing it all. My mix comes from a bag, I add perlite and my trees love it.

Most of the media offered in this area (NC) seems to be pine bark based and it breaks down in about 18 months. It was my citrus trees needs to be re-potted every other year that drove me to the cage pot idea. I use bagged soil-less mix and add in gravel or permatil (expanded shale).

My kumquats soil uses
1 part crushed bricks, 1/4 inch to 3/4 inch particles.
1 part gravel 1/8 inch to 3/8 inch particle size.
1 part sand very small to 1/8 inch particle size.
3 parts totally compost leaves & grass, & veggie scraps (black platinum powder)
The bricks are a porous (to be painted type) and water absorbent,

My sweetlee tangerine trees is in a mix of 50% garden dirt and %) of the totally rotted leave, grass, and veggie scraps. This tree shows some sines of soil a little too heavy but otherwise does well. My poncirus Trifoliata a does very well in the same mixture. My 2 Meyer lemons in the same mix do somewhere between the sweetlee and PT. My in ground PT and 2 Other Sweetlee are planted in top soil from the yard and I mulch with somewhat composted leaves.

I would suggest the soil mix I used for my kumquat if you make your own. It works very well. It holds enough water, does not get too soggy, and accepts water readily even if it dries out.

I would suggest that you use the 5-1-1 mix. It is proven and will need replenishing as often as your tree's roots will need maintenance.

My mix was free. I swept up the sand and gravel from my streets gutter. The bricks were from a tear down. The compost is from my own yard and kitchen.