I am shopping for a new grow light to add supplemental light for my small forest of trees, and I'm having a very difficult time determining which type of light I need.

All of the research I've found simply states that exotic plants all have different needs. For citrus, what type of bulbs are best (Metal Halide, High Pressure Sodium, LED)?

My plants will be inside for the winter, and I don't have the option of giving them direct sunlight. They will be near a north facing window, so I'm concerned they won't have enough light, and considering I live in Central Ohio, the days will soon be very cold and short. My plants are all young, (under 3 years) but I have a lemon tree that flowered this summer.

I use Metal Halide lighting from sunset until 10:00 PM during the short days of winter. As you live in Ohio, and your tree will be spending it's entire winter indoors, to insure the continued health of your tree throughout the winter, it is much more important to heat the growth medium than it is to light the foliage. Keeping the container between 64 to 70F will provide a much greater benefit than will lighting. The best, of course, will be doing both heating and lighting. The only tree that I bother to light, and I am currently growing 127 varieties of citrus, is a Marisol Clementine, I also heat the soil to 80F for the entire winter. This tree is now three years old and is planted in a raised bed in my greenhouse. The tree has produced five flushes of growth ever year and is now approximately six feet tall and five feet wide. Due to evaporation from the container, the growth medium will always be cooler than the air temperature of your home. The danger of winter leaf drop (WLD) is not as great in your case because the tree will not be setting in front of a southern window. A tree receiving a northern exposure has less of a chance of leaf drop, than a tree setting in front of a southern window. For containerized citrus trees the most important part of the tree, and the most difficult portion to maintain properly is the part growing inside the container. For a container tree, the health of the tree's root system should be of primary concern, and the scion (foliage) secondary. You should be able to find many many threads covering this subject on this forum by using the search function. Good luck with your trees. - Millet

Hi Everyone,i brought all my trees in and put them under the house for winter,Too much rain and wind in new zealand during winter months and both cause leaf drop. I have put them under a flouro tube,the ones that flick on and off a few times before they come on and used a 60 watt household lamp from another direction.Ive put it on from 9am until 10 or 11pm at night.
All my trees have done well and spring is around the corner.Lowest temps
outside here have been 5c,so not as cold as you guys.I was thinking of getting heat matts to put under the trees but it cost a bomb,so i havent
watered much at all.I have foliar fed(chelated)with the recommended 5/1/3 npk plus trace elements,with a tiny drop of washing liquid once a week,kept all the pots elevated and pretty close to the light source and all has gone well.However,i read on this forum that 12c or over was good to keep the roots active.I doubt if i have achieved this.
I have over past years killed trees from the outside conditions(wind/Rain)
but this year as autumn approached,i was careful with watering and once
indoors,tried not to water at all.I will give a good flush out in spring,when i
take them outside.I used an old photo lamp once(the metal ones),they gave off a lot of heat too,dont have that anymore.
The above lights(flouro etc) do give off some heat and do dry the
soil slowly but i would imagine nothing like the heat matts that millet mentions.They sound great.
I will be feeding with an NPK of 4/14/10 plus trace,in spring to
focus on root growth and overall strength of tree.Is this a good tactic
Millet? Regards to all here,i will post photo some time to show my efforts and good luck to writer of this post with your lights.Cheers
p.s keep sending those tasty florida navels over here!yummy!

Millet,
How long does soil retain heat? My plants will be in my home, and I'm not sure I'm comfortable with having heating mats, christmas lights, or heat coils on while I'm away from my home. If my home is kept at 65F, can I heat the soil in the evenings for a couple hours and the soil still retain enough heat until the next evening?

Soil does not retain heat long, at least 1 gal containers don't-- I'm sure larger containers would hold some heat longer, but the real question is what the soil temp will be when the direct sun starts shining on the leaves--if it is below the mid 60s F (55.6 F being absolute zero) you may get leaf damage.

I used the small Christmas tree lights last year for my seedlings aand they worked well for me. ( I used a graland type strand with 3 to 4 blubs per inch and just wove a single strand between pots).

Skeet is correct, everything is balance. High light/heat to the foliage (scion), requires high heat to the root zone (>64F). Root zone temperatures at or near 55.4F, citrus roots do not function, or function poorly, and therefore cannot supply cooling moisture to leaves that are receiving higher light temperatures. The tree tries to solve the imbalance by dropping its foliage in an attempt to get back into balance. - Millet