My Meyer lemon has aphids all over it and has lost its leaves! I just brought it inside for the winter. What can I do?
The aphids were more than likely already there, even if not enough for you to notice, and once inside the warm(er) house they multiplied. Aphids do love citrus plants. The leaves probably fell off due to the temperature change they experienced coming indoors.
The following information was found on p. 278 of the 2001 edition of the Sunset Western Garden Book:
Citrus in containers. Fertilize monthly from midwinter to mid-autumn with high-nitrogen liquid fertilizer, containing chelated zinc, iron, and manganese. Potted citrus … in cold-winter regions: shelter plants in winter; a cool greenhouse is best, but a basement area or garage with good bright light is satisfactory.
Many of the common products sold in nurseries or garden centers contain the trace elements listed in the Sunset info above. Also, there are specific formulations for citrus available, also carried by many nurseries and garden centers.
…Sunset Western Garden Book continued…Citrus as houseplants. No guarantee of flowering or fruiting indoors, though plants are still appealing. ‘Improved Meyer’ and ‘Ponderosa’ lemons [other citrus names omitted] are most likely to produce good fruit. Locate no farther than 6 ft. from a sunny window, away from radiators or other heat sources. Ideal humidity level is 50 percent. Increase moisture by misting tree; also ring tree with pebble-filled trays of water. Water sparingly in winter…
I grow 2 Meyer lemons and find that they do best outside until the temperature goes down into the 20s. They are pretty hardy. The aphid problem is not a problem outside until spring.
If you have a sun porch at your house, that might be a great place to put the lemon in winter.
As for the aphids, Colorado State University Extension provides information on insect control using insecticidal soap. You can purchase it or make your own: 1 teaspoon of soap (the mildest you can find) per quart of water, sprayed on both sides of the leaves and on growing surfaces.