Last winter I overwintered my two citrus, a Trovita Orange and Oroblanco Grapefruit/Pomelo hybrid under a metal halide lamp and they did just fine. I even ripened 4 delicious oranges!! This year, things aren't so well.

First off, the light intensity is lower, mainly because the trees have spread wider and in order to get the whole plant covered I needed to mount the fixture higher, in order to get the areal coverage I needed. Last winter, the upper leaves were around 4700 foot-candles and the lower leaves 1000 (500 in the most shaded lower inner leaves) and this year, max about 3900 and min about 500. More detail to follow:

Both trees had been outdoors all summer, and when night temps hit the upper 30s Sept. 25 I brought them inside. Turns out the first week of October was in the 80s but I asn't lugging them back out.

First the Trovita:

This tree is the larger of the two. Last year it ripened several smallish but very sweet oranges in January under the lights!! This summer the tree had a major scale infestation that scarred the fruits that had set in March of this year. However, they are quite large now although scarred but I have gotten rid of the scale-finally. However, since bringing the tree in, 2 of the 8 oranges just dropped off without warning today along with about 15% of the leaves. Last year I lost a few leaves when I made the outdoor-to-indoor transistion, but the fruits stayed. Then again, the fruits were smaller (it had bloomed late the first year) and fewer in number. However, since being inside the tree has actually made some new growth, but the growth has longer internodes and larger leaves than what had grown outdoors. Looks healthy though.

Then the Oroblanco-my problem child:

THis tree grew rapidly this summer and I do have a single grapefruit that set in May. It's now about 2.7" in diameter. However, it has lost over 50% of it's leaves in 2 weeks and more are yellowing. Only the "old growth" leaves seeem to be falling, anything that grew this past season is green and intact. The tree is more upright than the Trovita nad the way the branches are arranged, there's no way to place it under the light where the lower leaves aren't heavily shaded (500 footcandles or so at best) even when I have it next to the Mylar on the wall!! The upper leaves get light (>3000 FC) but I don't think there are enough leaves there to support the whole plant. I don't think it's getting enough light and I can't seem to arrange it any other way. Also the angles at which many of the shoots grow means the light hits at a sharp angle and is therefore not that intense on the actual leaf surface. Will it survive? I'm afraid it will be as bare as a deciduous tree by the time spring rolls around. Unlike the Trovita this tree is NOT making any new growth, in fact the Trovita has had 3 flushes in the time that this tree has had only one. Aside from the leaves that have dropped it looks healthy enough.

BTW the Trovtia is in Miracle Grow potting mix and the Oroblanco is in CHC/Peat. The Oroblanco seems to have a much denser root system though.