Thanks for your question.

With respect to the lemon tree in the pictures you sent, I have the following impressions:

1). There is widespread chlorosis in the leaves as evidenced by yellowing between the leaf veins. Although you did not mention it, if the variety of your lemon tree is either Meyer or Lisbon they have the highest light demand of all citrus trees. Even under your grow light, I suspect your lemon tree now being inside is getting only 10–20% of the summer light it had outside. This significant reduction in light can lead to leaf chlorosis, leaf mottling, and leaf drop. Often these symptoms occur after two to six weeks of being moved indoors. Since the stems of the lemon tree appear green and healthy, I would expect that the tree has not been significantly damaged.

2). With respect to your lime tree, it is far less susceptible to light reduction than is your lemon tree. This is the primary reason for the different appearances between the two trees.

3). Your lemon tree probably experienced stress in being brought inside. This transition would have affected the entire plant. Roots might have experienced a slowdown in growth. For sure, photosynthesis would have been reduced. Sometimes this transition will stimulate growth in the abscission region of the leaf. This is the area where the stem of the leaf attaches to the branch. Growth in this layer leads to leaf drop. As is true for light requirements, lime plants are far more resilient when moved inside than are lemon trees

4). Finally, your house is probably typical of most Minnesota homes during the winter months. The indoor humidity is significantly lower than outside humidity. This reduced humidity can promote leaf drop in lemon trees. Lime plants have a greater tolerance for dry conditions.

Moving forward, I suggest the following:

1). Increase the light Intensity around the lemon tree. Be sure that your grow light is between 6 to 10 inches above the top of the tree. Exposing your lemon tree to a second grow light would be an excellent thing to do. Use a full-spectrum LED grow light with a wattage of at least 150. Have these lights on for about 14 hours/day.

2)l. The humidity around the lemon tree should be at least 40%. Avoid placing your lemon tree near any heating vent or radiator. Ideally if you have a portable room humidifier, have this as close as possible to the lemon tree.

3). Do only very light fertilizing during the winter months. Whatever fertilizer you might use, apply it at only ½ the amount as specified on the product label.

See the following for information on these and related points:

https://ask.extension.org/kb/faq.php?id=426121 - :~:text=Expert Response,to dry out between waterings.

https://forums.botanicalgarden.ubc.ca/threads/leaf-drop-on-indoor-meyer-lemon-tree.94953/

https://extension.umn.edu/houseplants/growing-citrus-indoors - :~:text=Citrus plants grow best indoors with 65° days, dropping,before bringing them back indoors.

Good luck. Be patient. If you follow these suggestions, I believe that you will see significant improvements in your lemon tree within six weeks. The yellow and mottled leaves will probably not improve so they can just be removed at this time. New leaves should grow to replace them.

Thanks for using our forum. Please get back to us with any further, related questions.

Glad to be of assistance.  As long as the stems remain a vibrant green, the plant is alive and kicking.  If you have a chance, send us a progress response around the middle of February.  Many thanks. 

Thanks much for getting back to us.  We always enjoy follow-up questions.  I'll try to help you again but have four questions:

1).  With respect to spider mites, it appears that they are still there.  Are they on both lemon and lime trees or only on the lemon tree?  Have these mites been with you ever since our December 2025 chat?

2).  I don't quite understand the humidifier issue.  I don't know where your furnace enters into things unless there is a humidifier on your furnace and that is why you need to use distilled water. Please clarify.

3).  Are the yellow leaves that you show in the pictures the same leaves that were present last December, or are these leaves that have yellowed since December.  I am trying to decide if what you are now seeing is simply a carry-over from December, or if we are looking at some new developments since December.  What about the new leaves that developed this last February.  Have they started showing yellowing as well?

4).  Last December (2025) I made some suggestions about trying to increase the amount of light that the two trees receive.  In you latest update you said you did something about the lighting.  Could you please be more specific about this.  Although daylight is now increasing, what did you do to increase the amount of direct light that was received by the two trees?

Looking forward to hearing back from you.  Thanks.

Thanks for your latest information.

Let’s begin by reviewing your situation:

1). You first contacted us on 12/1/25 about your lemon and lime trees. They had been outside during the previous summer. After bringing them inside for winter keeping, the leaves on both trees started to yellow and fall off.

2). We responded to your inquiry by acknowledging the presence of significant chlorosis (yellowing) in the lemon tree and to a lesser extent in the lime tree. We suggested that some of these events could be attributable to the shock of being moved inside.

3). We further suggested that you increase the light intensity to which these trees were exposed inside. We stressed the importance of increasing the humidity surrounding the trees. We also mentioned the desirability of reducing the amount of applied fertilizer.

4). Now in March 2026, and perhaps even earlier, spider mites are infesting the lemon tree. I don’t think you’ve made any mention of spider mites on the lime tree. That you have these trees in different rooms of your house may mean that these mites are currently confined only to the lemon tree. I tend to doubt this possibility.

5). You increased the humidity around the lemon tree by, presumably, a portable humidifier. Now you are discovering that white residues are being left on certain surfaces in your house. This increased humidity also appears to be having adverse impacts upon the filters attached to your furnace. I think that both events could be attributable to salts found in your tap water. This is why the use of distilled water, expensive as it is, was suggested to you by your furnace folk.

6). In February 2026 you noticed new foliage on the lemon tree. Some of this foliage has now started to yellow. There has not been any new foliage on the lime tree and yellow leaves still exist.

7). By purchasing an additional lamp, you have increased the amount of light impinging upon the lemon tree. In part this may be responsible for the new foliage that appeared. It does not seem that you have changed the light exposure on the lime tree.

Going forward, I suggest the following should be done before moving these trees outside (presumably in mid to late May):

1). The spider mite problem needs immediate attention. An infestation of these critters can cause weak foliage development, leaf yellowing, and leaf drop. They could certainly be responsible for the yellowing that developed on the new lemon tree leaves. Take each plant to a sink, shower region, or out to a deck. Spray them thoroughly with lukewarm water, focusing on the undersides of the leaves. Following the spraying, apply an insecticidal soap or horticultural oil to both sides of the leaves. Be sure to use a product that is intended for spider mites. Then bring the trees back inside. Repeat these steps every five to seven days for at least three treatments. This should get rid of most of the mites but don’t expect to observe immediate improvement in the leaves. See:

https://www.houzz.com/discussions/5927415/container-meyer-lemon-persistent-spider-mites-leaf-drop-please-help

2). For the time being, continue with the current light situations. In addition to the artificial lights, moving the trees to sunny windows wouldn’t hurt.

3). Get a hand mister pump and spray the leaves on both trees daily using tap water. This would eliminate the need to get distilled water.

4). Try to find a citrus-specific fertilizer. Ask around at gardening centers. Get a fertilizer that contains iron, magnesium, and manganese among other things. Apply this fertilizer at ½ strength as long as the trees are inside. Increase this to full strength once you move them outside for the summer.

I would expect both trees to show considerable improvement once they get outside for the season.

Good luck. Always a pleasure to assist. Get back if you have any questions.

Glad to be of assistance.  Please get back to us with any further questions.