Imagine your tree growing in its full-growth habitat. If the immediate area lacks what that tree needs, its roots branch out into other areas to get nutrients. Now, look at your bonsai in a pot. When the nutrients in the potting medium are depleted, you have to replenish the nutrients by applying fertilizer. In addition, bonsai trees, grown in containers, require soil that’s much more porous to ensure appropriate aeration and drainage. Plus, there’s a much smaller volume of soil.
Therefore, you need to fertilize your bonsai to sustain the robust health of your tree, following some fundamental guidelines.
Nitrogen (N), phosphorous (P) and potassium (K) are required for cell division and the enzyme process that allows photosynthesis and growth. Finding the balanced bonsai fertilizer set that adequately supplies your plant, encouraging it to grow at a moderate rate, have good color, and show vibrant health is your goal. Simply, you need to supply the right fertilizer in the appropriate amount at the optimum times to sustain healthy roots, vibrant foliage and the seasonal requirements for your bonsai.
When do you need to fertilize your bonsai?
This is an age-old question with many “answers”. However, take into consideration the age/maturity, species and climate of your bonsai. Your bonsai’s response will be different, based on:
• growth rates – between species and within species
• length of growing cycles
• kind of root system
• abilities to absorb nutrients
The convention for when to fertilize is when a plant is in active growth, primarily in the Spring and early Summer. However, if you have tropical plants, you must be more attuned to the subtleties of their growth/resting periods than might be more obvious with a hardy-growth variety that has a natural dormancy in Fall and Winter. Learn your bonsai.
Remembering that a plant will only use as much fertilizer as it needs - how much to fertilize is, also, a question. Checking the over-all health of your bonsai will give you the answer. If the foliage is yellowing, if it isn’t flowering or bearing fruit – these are indications that your bonsai might not be getting sufficient nutrition.
What you’re mostly likely looking for is a range rather than a hard-and-fast level of when and how much to fertilize. Also, whether you choose organic or inorganic bonsai fertilizer has been rigorously debated. In either case, follow the directions, diluting appropriately depending upon how often you water, the species and the time of year, check the health of your bonsai, and adjust accordingly.
To encourage the growth and health of your bonsai when choosing your bonsai fertilizer, nothing trumps a good understanding of how and why your bonsai grows.