Bonsai is the art of training small trees in pots to resemble larger, much older trees. Bonsai is an ancient art that originated in China and moved with Buddhism to Japan. Although bonsai is often associated with Japanese culture, the practice is very popular in many parts of China. In growing bonsai, fertilizer can help keep trees healthy and growing.
When to Fertilize
Bonsai should be fertilized beginning in the spring. A tree will benefit from fertilizer throughout the summer and into the fall. However, as the weather cools off the tree's need for fertilizer drops off. By mid-fall, you can stop giving your tree fertilizer for the winter. Trees require no fertilization in the winter.
Bonsai can benefit from many organic fertilizers. Fertilizers that are higher in nitrogen---like fish emulsion, fish meal or seed meal---can help green growth of trees. If you are growing a flowering bonsai, like an azalea, use a fertilizer with less nitrogen, like kelp emulsion, in the spring and through the flowering season of the bonsai. After the flowers have dropped, switch to a fertilizer with more nitrogen.
If you want to use chemical fertilizers on your bonsai, use a balanced fertilizer that is relatively low percentage, like a 10-10-10 fertilizer. The three numbers are called N-P-K numbers, and indicate the percentage by weight of nitrogen, phosphorous and potassium.
Bonsai trees drain quickly and are watered often. As such, you need to fertilize frequently, or risk having the fertilizers washed out in the process of watering your trees. The best way to fertilize your trees is to mix your fertilizer at half strength and use it in place of water according to a fertilization schedule.
The fertilization schedule for each plant will depend on how often you water the plant. Ideally, you should fertilize your bonsai with half-strength fertilizer every week or two. Depending on how often the tree needs water, you might consider replacing water with the dilute fertilizer every third watering or even every other watering. If you are using chemical fertilizers, be sure to read the label to avoid over-fertilization.