One of the commonest questions I get from readers concerns plants they receive as gifts during the holiday season. Let's take a look at a rosemary tree actually a topiary. A rosemary shrub was pruned to resemble a tree. It's beautiful. You are delighted with such a lovely gift. What do you do now? Help!
If you take proper care of rosemary you can grow it indoors for many years. Don't worry about having to prune it to keep the Christmas tree shape for a long time. Rosemary usually grows slowly indoors. Take a look at the bottom of the pot. Hopefully it has drainage holes because rosemary doesn't like wet roots. If you see roots coming out of the drainage holes of the pot you can trim them off but this actually indicates that the rosemary should be in a larger pot. If necessary transplant the rosemary into a pot filled with cactus mix. The new pot should be only one to two inches larger in diameter than the original.
Hopefully you were given a healthy plant. Touch the needle-like evergreen leaves. They smell somewhat like camphor even though this plant is a relative of mint. Take a closer look at the leaves . They are green on top and white below. This is normal. Hopefully you will not see a pile of dead leaves near the base of the plant. ( If you received a sick plant you won't feel so bad if it dies later on in the season. )
To keep your rosemary plant healthy, place it in a bright window where it will receive at least six hours of light per day. A southern or western window is best but I have had success with a northern bay window which is never in shadow. Rosemary hates drafts from open doors or windows and gusts of heated air from heating vents. These conditions shock the plant causing it to loose needles.
Rosemary likes regular watering so don't let it get bone dry as this will also cause the plant to lose needles. Stick your finger into the soil to an inch or so. If the soil feels dry, add water until it comes out the drainage holes. If you keep the pot in a saucer be sure to pour off any water that accumulates there to prevent root rot. Most sources will tell you not to fertilize rosemary during the winter. This is a personal matter. I simply take water from the fish tank each time I water. My feeling is that this way the plant receives a constant source of dilute nutrients.
You don't have to simply look at your rosemary plant. Harvest some of the leaves for cooking (especially lamb). Include some needles in a potpourri. Once in a while check the plant for powdery mildew. This is a fungus which makes the needles look dusty. Powdery mildew weakens the plants by taking up the nutrients that help it grow. Although you can apply fungicides I never do. Periodically I wash my plants in a sink using a sprayer in combination with my fingers. If a disease is present I wash the plants with a very dilute laundry or kitchen detergent solution. This takes care of the problem.
When all danger of frost is past you will be able to place your rosemary topiary outdoors. It will grow rapidly in the warm sunshine. You will be able to prune the plant if you desire. When autumn returns it will be necessary for your rosemary to return to the indoors. With proper care this is a plant that you will enjoy for many years to come.