Q. I have a lot of freshly chopped tree trimmings, which I want to use as mulch for shrubbery and vegetables. Will they take nitrogen from the soil? Should I add nitrogen to this material to compensate? A. The material is high in carbon, with a C/N ratio of 30. This causes soil bacteria to multiply enormously; and they take phosphorus and nitrogen out of the soil. Apply a dusting of 5-10-5 or 10-6-4 fertilizer before mulching with it, or compost the material before using it. Q. We have a beautiful American holly tree. Can we take cuttings from it and root them? A. Cuttings of American holly taken in mid- to late June root readily. Q. We're going to have a vegetable garden this year for the first time. Should we buy plants from a garden center or grow our own from seed? A. If you can get plants, you may be much better off buying tomato, eggplant, cabbage and broccoli plants at a garden center. If you have a sunny windowsill of a cold frame, or can use fluorescent lights, it may be fun trying to grow them yourself. Q. I was given a beautiful gardenia plant for Easter three years ago covered with flowers. It hasn't bloomed since. What does it need? A. Gardenias sold as potted plants are varieties of Gardenia vietchi. They develop flower buds only when the night temperature is below 65 degrees F. and above 60 degrees. The day temperature isn't important as long as it's higher than the night temperature.