As temperatures begin to get cooler and the days get shorter, all citrus grown in cold climates need to be prepared to be brought in for the winter. This routine needs to be gradual to ensure that the plant does not get shocked by too quick a climate change.
The most important consideration in transitioning to indoors is watering. As the days get shorter, the plant's growth rate slows considerably. This results in water needs that are quite a bit less than in the spring and summer. Start to pay close attention to how wet the soil is. Do this by checking with your finger pressed into the soil up to the second knuckle. This is the most accurate way to become familiar with soil on the dry side. You want to check the soil just before watering. The soil's moisture content will differ with the conditions that your plant is exposed to and requires your attention and understanding of how it is reacting to watering. Water only when the soil is on the dry side.
Next, gradually move your plant from its summer location by choosing a place close to the house where it will get radiant heat from the house - porches with good sun exposure or outside walls adjacent to rooms that are typically heated with good sun exposure are some examples of interim locations to acclimate your plant. Keep it in this location until the nighttime temperatures get into the mid- to high-30s. The longer the plant is outdoors with nighttime temperatures above 35 degrees, the better.
Next, choose a location indoors that has ample exposure to sunlight. Big, bright South to Southwest facing windows are usually good. Keep in mind that this may not be enough and additional lighting may be required. When choosing indoor lighting for indoor winter growing, avoid full spectrum lights that are more for promoting growth. This is contrary to what the plant is doing naturally at this time of year and can be detrimental to acclimating your plant and ripening fruit on your plant. Instead look for LED lights that are in the spectrum for flowering and ripening fruit.
In addition, the location that you choose should be away for any heat sources such as vents, heaters and wood stoves. The dry conditions indoors lack humidity, which is another challenge in overwintering your citrus tree. In severely dry conditions, humidifiers can help when placed in close proximity to your plants.
Feeding your plant before bringing it indoor is ideal. Use an organic acid base fertilizer and feed as you begin to adapt your plant to the move indoors. Feed again about 30 days before you move the plant back out.
It is ok to transplant your citrus into a desired container when you receive it. A 16 inch pot is recommended for a #3. Once planted, DO NOT repot your plant during its time indoors. This almost always results in the loss of the plant. We never recommended this. If repotting is required, wait until late winter, early spring or just as you transition the plant to the outdoors.
Watch for insect problems which often occur when the plant is brought indoors. Mites and scale are the two most common and if caught early they are easy to care for. Small black bugs coming out of the soil are most often fungus gnats - and a sure sign that you are overwatering.
Last, yellowing leaves and leaf discoloration are common when bringing plants indoors. The goal is to bring the plant indoors as healthy as possible. A plant brought indoors with foliage discoloration will rarely recover until the following spring. If your plant is discolored when coming inside, follow the instructions above. Resume working on improving the health of the plant the following spring.