I never thought I could grow citrus in Minnesota. I mean, seriously, you are hard pressed to find fruit besides apples, cherry, or plum trees.
So in my search to grow something different, I started to peruse any Northern University websites that had any information on growing citrus indoors. I was quite happy with the results.
First I discovered that most common varieties of citrus grown in the US are far to large to grow in the northern climates because citrus trees up here will need to be over wintered indoors. That led me on a quest to find the smaller varieties that would be easy to transfer inside and out as the temperature allowed.
Here is what The University of Minnesota says about indoor citrus:
Citrofortunella mitis, or calmondin orange, is probably the most common species grown indoors. Its fruits are small and sour but can be used for marmalade or as a garnish in summer drinks. The Otaheite orange is not actually an orange but is a dwarf, spineless variant resulting from a cross between a lemon and a tangerine. Its botanical name is Citrus limonia 'Otaheite,' once known as Citrus taitensis.
Tangerines (Citrus reticulata) can also be grown indoors. Satsuma oranges, which are really tangerines, are particularly good and are noted for their abundant fragrant flowers. There are two varieties of lemon which may be used as houseplants, 'Ponderosa' and 'Meyer'. Citron (Citrus medica) and kumquat (Fortunella species) can also be grown indoors.
The culture of citrus plants is not particularly difficult if the following requirements can be met.
- Temperature: Citrus plants grow best indoors with 65° days dropping five to ten degrees at night.
- Light: Some direct sun is desirable for at least part of the day. During the summer, citrus plants may be placed outside to take advantage of better growing conditions and extra light. Let the plants acclimate to sunny conditions by placing them in the shade of a tree or north side of the house for the first several days. Make sure they have plenty direct light eventually. Re-acclimate them to lower light at the end of the summer by keeping them in a shady place for a week or so before bringing them back indoors.
- Soil: A soil containing a fair amount of organic matter (leafmold, peatmoss or compost) is desirable. Since citrus plants prefer acid conditions, use peat in the potting mix to help keep the pH down. Use about one-third sterile potting soil, one-third perlite or vermiculite, and one-third peat or other organic matter in the potting mix.
- Fertilizer: Use a fertilizer formulated specially for acid-loving plants, mixed so it's half the recommended strength. Fertilize the plant only when it is actively growing, usually April through August or September.
Pests: Scale, whitefly, and spider mites are some of the more common pests of citrus. Many insects can be prevented from gaining much ground by making sure the foliage is kept clean by periodically washing the leaves. Pay special attention to the undersides as well as the tops of leaves. To treat insects chemically, check garden centers for products currently approved for use on houseplants.
Propagation: Generally stem cuttings root easily. Use new shoots which have been allowed to harden just a little. In other words, the shoots are not buttery soft and have a little substance to them. Usually, these cuttings are taken in the spring or summer when the plants are growing most actively. Root the cuttings in fresh potting mix, keeping them slightly moist. Repot when new roots reach a length of one inch or so.
Seeds also grow quite easily, though they will usually not yield plants exactly like the parent from which they came. Plants grown from seed seldom attain a large enough size to flower and fruit. Growing citrus from seeds is a good children's project, though. Using the same potting mix as you would for cuttings, place seeds about one-fourth inch below the surface of the mix. Again, keep the potting soil moist. (Source: By: Deborah L. Brown, Extension Horticulturist)