No. They need light and cold. The light does not need to be of growing intesity but they will need extra light. You are going into summer now. Any light you give them in the basement is heat that will not be need from your furnace. It kind of balances out things.

Steve

I overwintered the majority of my citrus trees in a north facing sunroom which basically is a glassed in porch with very little heat and no sunlight. The room was not very bright, but the trees adjusted. The temps ranged from 45*-55* depending on the outside temps. It can be done, but you really have to be careful with the watering.

mine died in the basement with a window. I would say to leave them with as much light as possible.

You will need extra lighting on timers, plus you will need to keep the air temperature between upper 40s to 60 degrees. NO WARMER! And add a fan for air circulation. The dimmer it is, the cooler they need to be. They should be discouraged to grow. Cool temps keep pests at bay as well. If you need to crack open a window to get it cooler, that would be one way to go.

Vladimir, not sure if you are being forced to give up your space and greenhouse and if so I am sorry about that. You will adjust)

All the answers are very good above. The less light the colder they should be. Under 50 at least. If you keep them warmer than that, you could use a nice light set up and do it that way, like what Laura uses.

If the basement has power and water, has average temperatures approaching 70, why not try setting up some lights and grow them indoors off season. I do and get them to fruit and flower. i actually regret putting my trees out so early around April 15th, they've done nothing for a month and only now are perking up....from now on out late after May and in early in October

Thank you everyone for your comments. It looks like it can be done. I know that the Italians, French and probably some others have been overwintering theirs for centuries in orangeries and lemon houses that have little supplemental heat. I saw the orangerie at the Luxembourg gardens this past August and it had huge windows and a lot of light.

My problem is how do I determine the balance of amount of supplemental light and temperature? For example: What is the relationship between foot candles and temperature?

Vlad, I didn't have anyway of measuring the foot candles and I am too cheap to buy in instrument to do so as my method worked for me. I hope you don't have to learn the hard way.

I think you should start with temperature and work from there. You want a cool room. How cool can you keep it? Either way you need supplemental light, but if your plants are going to be in a warm room, you'll probably need LOTS of LED units and/or perhaps a High pressure sodium lamp.

With lights on a timer, set to below 12 hours for most of the winter. Then as spring approaches -- (spring for citrus is usually February!) -- start adding time to the day length. This may coax them into bloom.

4 or 6 bulb x 4 ft long led replaceable bulb fixtures can be using daylight LED, depending on plant size and qty, you made need 4 fixtures and bulbs, power strip (some have built in timers)...an investment for sure....but the payoff comes around Christmas and new years on, when you have things blooming and fruiting indoors, basements and cellars are generally cooler than above floors

Vladimir, I don’t know if it will help but I can share my growing setup. I put all my citrus trees (well, what can fit) in a 6 x 4 grow tent located in my basement (no window). The thermostat in my basement is set to 45F during winter and it’s pretty cold there. In my grow tent, the temperature can go down to 55F during the night and goes up to the 60F something during the day in the coldest of winter. Otherwise it’s pretty much low 60F during the night and 70F during the day. The heat comes from all my artificial lights.

In my grow tent, the only light are from a 1000w led and three ikea lamps for the corners (same than Laura).

https://www.amazon.ca/s?k=bestva+1000w+led+grow+light&crid=P6TH6Q2U2NMU&sprefix=Bestva%2Caps%2C139&ref=nb_sb_ss_i_2_6

Some trees are growing in this conditions and some go to dormancy but I think it depends on the rootstock but I am not sure. Per example, I noticed that all my trees on x639 rootstock don’t grow much in my conditions. All my trees on C35 or Carrizo seem to grow very well.

Oh and the reason why I use a grow tent instead of just putting my trees directly in my basement it’s because my husband don’t want to have moldbecause of the high humidity coming from my trees.