Citrus Help For the Land of Ice and Snow

Q. I live in Michigan, so our experience with citrus is non-existent, and there are no experts in our area, but you come recommended as someone who might be able to give me some advice. 
I have a small potted orange tree with a few leaves that have turned light colored along the edges.  They aren’t yellow or brittle as one might expect in the case of iron deficiency, but are shiny and flexible like the rest of the leaves.

I bought the tree on a lark, never expecting it to survive, but it thrives except for these few leaves.

The plant is outside, on the east side of the house when the temperatures will stay about 40ºF.  The rest of the time (about 7 months a year) it is inside, on an east facing but brightly lit porch.  It has never been frosted.

The tree has been potted for 2 ½ years.  I have not re-potted it.  It is about 14” tall.  It was originally potted in soil that was 50% commercially prepared potting soil and 50% composted leaves.

Our water is very alkaline, so during the winter I water with black tea, made with distilled water and fertilize at about half strength with Miracle Grow.  During the summer I water with rainwater and fertilize with the rest of my plants, again using Miracle Grow, this time at recommended strength.

Have you any suggestions for me?  Any advice would be appreciated.

A. It will be fun for you to grow a citrus in Michigan. I am originally from Wisconsin so I can understand your interest in having a citrus growing in Michigan. First of all make sure the container is large enough for your tree. It will need to be fairly large.

Secondly the tree should be removed from the container every 2 to 3 years and wash some of the soil away from the roots. Cut off some of the roots near the outer edges and repot the citrus in the container using new potting soil. In two or three years the organic matter content of the soil in a container will be gone. The soil would become more compact and the roots of the tree will begin to suffocate. Water will not flow through the container as easily as before. The air spaces around the roots collapse. Root rot begins to set in and this usually causes leaves to start scorching on the edges, yellowing and falling from the tree. Repotting the tree every 2 to 3 years and trimming off some of the excess roots helps to keep the tree young and vigorous. Using new soil increases the air spaces around the roots and helps keep them healthy. When you take the tree out of the container, look at the roots. Healthy roots are creamy white. Roots that are beginning to die turn brown.

When you repot the citrus also reduce the size of the canopy or top of the tree. Look at stems that are too close together or on top of each other and remove them totally. Avoid giving the tree a "Butch haircut". You will generally thin out the branches and open the canopy. If some of the limbs are too long, cut them back so they are shorter and reshape the tree.

Leave the citrus out in the container outside as many months as you possibly can during the spring, summer and fall. They can take reduced sunlight for maybe two or three months but no longer than this. It sounds like to me you are keeping them inside too long. If you have a warm spell during the winter when it's not freezing, put it outside and let it get lots of sunlight. The tree will store this energy inside of its trunk and limbs and live off of it for a time when light level is low and inside the home. If you can put a florescent light close to it, a few inches away, leave it on for 12 to 14 hours or longer each day when it's inside. This will help a lot.

A common problem on citrus are scale insects, usually brown scale. Look for these brown bumps on leaves and stems. If you find them, use a horticultural oil and spray the leaves and stems with it about once a month and you will start to see the populations of this insect decrease. Brown scale and root rot because of watering too often or poor drainage and a lack of sunlight are the worst problems.