The white flowers and green leaves of a gardenia bonsai make an elegant statement. Combined with the fragrant scent, it is easy to see why the gardenia is a popular plant to turn into a bonsai. Here are a few tricks for growing your own gardenia bonsai.
Use a soil mix that is slightly acidic with a high percentage of organic material. Soil should be kept between a pH of 4 and 5.5.
Gardenias are a tropical plant that likes sun, so they require a good amount of water. Observe the soil of your bonsai daily and keep the soil good and moist. Over-watering is safer than under-watering, though there will be consequences for both. Over-watering will cause the roots to rot, turning black. If you find your roots turning black, trim the damaged roots before repotting and try a little less water.
Gardenias prefer sun, but not too much. They should be in the sun for 3 to 4 hours a day. If you keep your bonsai outside in hot weather, put it in the shade of a larger plant to protect the leaves.
Use a fertilizer designed for acid loving plants at half strength every 2 to 3 weeks from spring to autumn. Do not use a rapid growth fertilizer, as your goal is to keep the bonsai miniaturized. Do not fertilize while the bonsai is blooming. Gardenias may also benefit from chelated iron 2 to 3 times a year.
Another way to manage the acidity of the soil is to use water mixed with vinegar: 1 tablespoon of white vinegar per 1 gallon of water. Use this mix to water your bonsai once a month.
Repot your gardenia bonsai every two years after blooming is complete. Before installing the plant into the new pot, trim the hairlike root structure by 10%. This will limit growth without damaging the plant's ability to absorb nutrients.
Prune after the flowers have died in the late spring. Be careful not to damage the leaf buds as they are setting for the next year's growth.
Wire gardenia bonsai between the late spring and autumn. The branches are delicate, so bend gently to keep from breaking them. Be careful not to damage the leaf buds while wiring. When in doubt, wait until later in the year before wiring.
The most common style for gardenia bonsai is the broom style, where the bottom third is a thick trunk and above that the branches spread wildly. This style can be achieved predominantly with pruning and a minimum of wiring.