Hello all,

I have 1 big meyer lemon, 2 small navels, 1 medium lime, 1 small lemon and 1 caldomin.

Most were fine with the transition from outside to inside window ledges for the winter, however:

the 2 small navels lost all their leaves, 1 is turning brown, the other seems to be regrowing.

the big lemon lost most of its lower leaves, the upper still has life.

i guess this is due to stress? i must admit as cold was approaching fast i did not slowly move them over.

they are all planted in chc's with slow release so doubt its a water thing.

is there anything i can do to cheer them up?

ps am i right in thinking i do not have to provide them light over winter? they will just go dormant in pitch black?

your help is as always appreciated

ben

If the trees were exposed to temperatures below 55 while still outside, it is possible that the roots were already dormant and could not supply water to cool the leaves and therefore the leaves overheated and will drop. The dropping will continue for a while, but the trees should recover.

If you have put them in a place where they do not recieve direct sunlight, they should be OK without additional light as long as they are not exposed to freezing and the temperatures remain below 70.

Change in average sunlight hours can trigger also leaf drop.

Thats what it probably is, the light change, the roots did not get cold.

I do have a heat mat, perhaps I should set them all up on that?

If they are not going to get direct sunlight for several hours a day, it would probably be best not to heat the roots. That would be like putting a black bag over them during the summer-- the roots will be active but can't get food (starch).

I am surprised that a tree would drop all of it's leaves due to a change in sunlight hours though?

To obtain the maximum production of energy for the tree a citrus leaf only requires a light strength of 650 PAR, which is not even full sun light. Therefore, I would heat the trees root zone to a temperature of 70F until the leaf drop stops. After the leaves have stopped dropping from the tree you can either keep the container heated to 70F, or drop it back to 64F. - Millet

Well Joe,
since Ficus is completely different to Citrus, as the one is completely tropical and has only some non-tropical varieties, the other is non-tropical with only some being adaptable to tropicals
So most difference in Ficus benjamini is the facos, that F. benjamini is climber! Yes!
The seedlings grows in the shade of trees in rainforrests and uses the stem of those trees as hold. Than, after reaching sunlight, it will branch up, starting esablishing a crown, and then developing more and more braches, and air-roots gowing downwards till a complete wrap around the tree is made by the Ficus... and this will gridle the tree, the tree will die and remaining only the dense hollow web of the now remaining Ficus benjamin.
Thus, adaption to sunlight changes are not in the margin of Ficus benjamin, as change in sunlight means a completely different reorganisation for this plant.

In Citrus the change in sunlight is hardly discused, but only to evidences found, but not real mechanisms were discovered (see: Biology of Citrus, Spiegel-Roy and Goldschmidt, Cambridge University Press)
So the only thing we know and can be sure, is the precence of shade leafes inside the canopy. But thining and leaf drop inside the canopy is not because of absence of light, it's more evident, that those leaves were discarded because of expansion of the outer leaf volume, so that the little sugar produced by those leaves can be completely replaced by more outer leaves.
So in our circumsance leaf drop, in my honest opinion, does not come from light. Because you can give a tree less light outside, and if you place it inside with more light, you will find that those trees well sheed leaves as some decidous trees. That's very severe, because all leves had to be replaced, and that's a strong factor of taking those power from the reserves in the woody parts of the tree, not seldom you can discover even death of young and tender twigs, because getting fully depleted of strach.
So that leaf drop does not come from light, it comes because of cold roots, which are unavailability of water to the leaf surface, which is required for respiration. Citrus is a C3 plant, and needs up about 7/8 of water only for respiration and only 1/8 will get into photosyntheses (see again Citrus Biology), in optimum circumsances 1/5 of all water goes into photosyntheses.... but consider the most influence and hard influence comes from the root system which is very tender to temperature changes (see Olson and Wutscher: Root Temperature trials in Texas by the A&M Citrus Research Center) and the effects are very much dinstinct as in light changes to the canopy.

Thus, yes there is evidence for leaf drop by light, but no, it's not so hard, that we can consider bringing the tree from outside to the inside and only the change of light will cause leaf drop.
So bringing the tree usually from "full" sunlight to "less" sunlight indoors, the less light will give more the impulse to the tree to procude more leaf volume, rather to shade leaves. Because it's for the tree possible to transform light-leaves to shade-leaves, as making light-leaves from shade-leaves, because the complete leaf lamina has to be changed.
So we bring our trees usually to less light conditions indoors, so there is no real reason why a tree should drop leaves, because the tree has a negative light/sugar ratio, so has to build up more active leaf surface or more efficient leaf surface by more shade-leaves, to bring the metabolishm to a positive side, as the keep it negative, which means the the tree always will need up the reserves found in wood and root parts. It makes no sense and is not considered by most experts. This will mean for humans: As oxigen gets lower in athomsphere high, you have to simply stop breathing... makes also no sence...

So, if you provide less light, simply hold the tree at a good root temperature, to optimze the other factors of growth. Some leaf drop may occur, but because of accumulation of absission acid, as because of change of light.
So many orangeries were still today not realy bright, but the cool temperatures does not make the tree able, to have a need for such much or intense light, the balance of root temperature and light is given and no leaf drop will occur, even in the past days, as orangeries were often so dark, that the gardener needed a hand-light to find the path through the trees (compare Comelyn: Netherlands Hesperides and Volkamer: Nürnbergische Hesperides)
So leaf drop is not by light, that severe, it's more the imbalace of root temperature and given light.
If you do not belive, simply test....

So Steve, if I understand correctly, you are saying that the temperature does not have to drop to 55 F to create a problem, but any relatively sudden drop will leave the roots unprepared to supply the necessary moisture?

Skeeter,
in priciple yes, but it will not be that severe if temperatures remain well above 15°C, also if during daytime the temperature raises again to provide sufficent root activity.
But if the temperature drops and the tree will get close to biological zero, it will stress the tree much more.
And seldom light changes, which can occur more and much harder within hours, will provide such effects...
So temperature, close to biological zero will stress the tree, and if you now shelter the tree indoors, were no wind will cool the leaf lamina, light will exhibit a heat source for the leaf surface, which needs respiration for cooling purposes by water evaporation through the leaf surface... So here the roots remain cooler for a much longer time as the leaf surface, because the sunlight will much quicker heat up the 'dark' leaf surface, as a large mass of compost in the container... So the imbalance of activity crown/root ball is in such conditions much sharper and more severe as outdoors, so this imbalance in water demand and water delivery by different active parts of the tree (leaf = higher temperature = more active versus roots = cold = lower acitivity) will stress the tree much higher, and will cause more leaf drop....

Because many of you tell about heating roots and the cause of leaf drop, so I was guessing you did see the whole process and understand, that light isn't that major factor in leaf drop....