So I've had all the citrus indoors for about 3 weeks now (in Atlanta, GA), and now that its starting to get cold, some are dropping a huge number of leaves.

I live in an apartment on the 2nd story, and there is open air below my unit -- and I have concrete floors. Thsi means that the trees all sit on a pretty cold concrete floor. I keep the air temp just under 70 degrees, but the sun warms up the leaves, while I'm guessing the roots stay cold - in the 50s to 60 is my guess.

Right now I'm trying to decide whether it would be better to try and insulate the containers from the floor or try to build a coldframe outside on the balcony using double-layer poly sheeting and a heater to keep them just above 32 all winter?

Has anyone else found a good solution to this problem? I've read about the heating coils for the soil, but I've got 12 trees so that'd be a pretty massive operation to put coils in all those pots unless I'm mistaken..

Thanks for any suggestions.

Pelham

Your situation is easy to correct. The sun light shinning on the surface of the leaves, warms the leaves to a point that they require water from the roots in order to cool themselves. The roots are at or near 55.4F, which is absolute zero for root activity. Because the roots are cold, they are unable to function, therefore cannot supply the leaves with the required water. For the tree to get into balance, the tree drops all or most of its leaves. Solution: either increase the temperature of the root zone to AT LEAST 64F (at this point 70F would be much better), or reduce the sunlight falling upon the leaves, by moving the tree, or placing a curtain in-between the sun light and the foliage. It is much better to increase the root zone temperature. WLD (winter leaf drop) commonly occurs after a sunny day. - Good luck to this tree. - Millet

Millet,

Agreed - heating up the soil is what I need to do. I'm trying to figure out the best way to accomplish this without breaking the bank.

Any thoughts? Here are the options I'm considering
1) Just insulate the containers from the floor by putting a layer of insulating foam underneath them -- this should stop the cold conduction from the floor, but I still don't think the soil will get them very warm

2) Do #1, but also add generic heating pads (not ones for seed starting) underneath each pot to add heat. At $12 each and put one under each tree -- I could put them on a timer so they only run for a little while and don't overheat the trees. This would be expensive though -- probably over to $150 to implement, and I'd have all these heating pads that need to be individually plugged in.

3) Do #2, and also use a couple of long soil heating cables but instead of putting them IN the soil, just take a few turns around the outside of each pot, and then string it on to the next pot. This would probably take 2 ~50ft cables. These would be controlled by a soil thermostat. This would be about $75 to install - but I'd still have a cable strung around the room...

Any thoughts about these or any other options?
Thanks,
Pelham

I did an experiment two years ago with my papaya tree. I used clear mini-Christmas lights, one that you buy for $1.99 after Christmas for a string of 100 lights. I wrapped maybe 5 times per pot wrapped around outside the pot tight. I had three 7 gallon pots for two strings. I put them on a timer which turned on at night. I also put a thermometer 6" under the soil to evaluate the temperature. I am surprised how high the tempt of the soil went. I had to decrease the number of turns so the tempt stays on around 70* F.
I also add another string all around the branches thinking they may help for photosynthesis.
My papayas and citrus grew normally without any lose of leaves and stayed green all winter.
The drawback was my wife kept complaining about the ugly sight of my plants because it was located by the window sill on the east side of our dining table. The reason I placed them there was that was the only place where I can get the max sunlight possible during daytime.

Thanks for the idea -- I've got an extra strand of those lights somewhere... I'll give it a try tonight and see if it raises the temp in one of the pots enough. If it does, that sounds like a great solution. They can all go on the timers as well.

Its time for something serious -- I bumped the Hirado Buntan Pummelo last night and almost HALF the leaves fell off it! My variegated pink lemon isn't doing much better... I need to do something quick!

Thanks for the idea!

Pelham

I can attest to the effectiveness of christmas lights for warming soil. I haven't tried this on a large scale, but recently I did the following for a tarocco blood orange...

-Wrap hardware cloth around tree pot
-Wrap x-mas lights around hardware cloth (~25 feet worth from a 30W (100 foot) string), fastening where appropriate (I used thin gauge wire, but twist ties or the like would work nicely as well).
-Cover the hardware cloth and lights with a blanket (I used one of those sweet "emergency blankets" that look like a huge piece of aluminum foil).
-Put lights on timer, and away we go

The basic idea behind this... I got the hardware cloth and emergency blanket for free and wanted to use them for something. This particular tree is moved frequently, and wrapping lights directly around the tree pot requires that the lights be removed and re-strung every time I need to move it. Wanted to see how effective the blanket would actually be... given that the lights are removed (albeit only slightly) from the container, my thought was that the heat loss from the bulbs would not transfer so readily to the planting medium without something to retain it.

This particular pot has a large space at the top with no soil, and my "stick your hand in the open space above the soil line" test shows that the temp inside is much warmer than the ambient (ambient being ~60F). Soon enough I'll get a thermometer in the soil and see what sorts of temperatures we're actually achieving. Just for kicks, I'll do this with the blanket on and off to see what effect it has.

~Derek