Tending to bonsai trees is an incredibly enriching experience. As we cultivate all the right skills—from pruning and shaping techniques to creating just the right environment in which a bonsai tree can flourish—we are able to manifest a living piece of artwork that grows and evolves as we do!
Among this vital skillset is knowing how to choose the right fertilizer for bonsai trees, how to use it correctly, and how often. In fact, fertilizing regularly during your bonsai tree’s growing season is a must for its strength and survival. It is because we keep bonsai trees in small pots with limited substrate—often in indoor settings—that providing timely nutrients is absolutely essential.
Buying The Right Fertilizer For Bonsai Trees
Just like human beings, bonsai trees need both water and food to survive. In order to successfully renew its cells and produce new seasonal growth both above and below the surface of the soil, every bonsai tree will need all the right nutrients at just the right times.
You can compare picking the right fertilizer for bonsai trees to a person choosing to eat a healthy Mediterranean diet rather than junk food! Of course, bonsai trees have very different nutritional needs to human beings, so what exactly do they require?
Understanding What Your Bonsai Tree Needs
The physiology of plants is quite unlike that of animals. Specifically, they require three basic elements: Nitrogen, Phosphorous, and Potassium. When you pick up a plant fertilizer packet and see the letters ‘NPK’, this tells you that the fertilizer in question contains a formulation of these three key nutrients.
Each of these elements performs a slightly different role in the health of a bonsai tree. Growth of the stems and leaves of your bonsai tree is dependent on nitrogen, while phosphorous supports roots, fruits, and flowers while playing an essential part in photosynthesis. Potassium plays a role in root growth and also helps your bonsai tree ward off infection and disease. So, as you can imagine, all of these ingredients must always be accounted for.
Knowing Which Fertilizer to Choose
When it comes to choosing the NPK ratio of fertilizer for bonsai trees, there are two different schools of thought. Some growers prefer to use different ratios at different stages of the annual growing cycle, while others favor using the same, balanced fertilizer all year round.
In the former case, growers will reach for a more nitrogen-rich ratio in the spring, a balanced one in the summer, and a nitrogen-low mix in the autumn. These might, for example, be an NPK 10:6:6 mix, followed by an NPK 6:6:6 mix, and finally an NPK 3:6:6 mix.
However, increasingly, bonsai growers are sticking with a balanced NPK 6:6:6 ratio through every season and adjusting how much they give depending on both the stage in their bonsai tree’s annual growth cycle and its type.
Other considerations that you might wish to explore include choosing a more phosphorous-rich fertilizer for your bonsai tree during its flowering and fruiting season. It is also worth noting that as bonsai trees age, they usually don’t require quite as much fertilizer as they used to. We will come back to assessing this factor as well as signs of over-fertilizing in a little while.
Is Liquid or Solid Bonsai Tree Fertilizer Better?
Many bonsai growing beginners are fazed when they find that there are two different forms of fertilizer to choose from. However, both liquid and solid bonsai tree fertilizers can be used very effectively, as long as a few key things are kept in mind.
Liquid fertilizers are easy to use and safe to apply, however they do tend to leach quite quickly from the soil with continued watering, making regular application all the more important. Solid, pellet or granulated fertilizers offer far slower release but they must not come into direct contact with your bonsai tree’s roots as this may cause burning. You can buy special fertilizer guards to place in your pot to prevent this from happening.
What about Organic or Synthetic Fertilizers for Bonsai Trees?
While the idea of organic fertilizer sounds more appealing to many people, both of these options will provide the necessary nutrients for your bonsai tree. The difference is simply that organic fertilizers are made from natural ingredients like seaweed or manure, while synthetic ones are artificially formulated.
Synthetic fertilizers can offer the reward of higher nutrient density but this does increase the risk of root burn for your bonsai tree. To avoid damaging those delicate root systems, steer clear of fertilizers that contain urea—a rather heavy-handed nitrogen-boosting ingredient—and always follow instructions carefully.
How Often Should I Fertilize My Bonsai Tree?
The frequency with which you fertilize your bonsai tree will not be the same all year round. This makes sense when we consider that these spectacular trees require more nutrients when they are actively growing than they do when dormant or less active in the winter months.
Depending on the type of bonsai tree that you keep, you may need to use fertilizer over all four seasons or only during the spring, summer, and autumn. Starting in early springtime, you can begin fertilizing your bonsai every two weeks, and continue at this pace before slowing in fall.
Tropical and subtropical bonsai trees that retain their leaves all year round, as well as conifer varieties, can be fed less frequently—around once a month—during the winter season. In contrast, deciduous bonsai trees that drop their leaves should not be fertilized during the winter at all.
How Much Fertilizer Does My Bonsai Tree Need?
Another aspect of fertilizing bonsai trees is knowing how much fertilizer to use. This depends entirely on the product you have chosen. The best tactic is to read the instruction on the packet carefully and follow them to the letter to ensure that you don’t apply too much or too little.
As your tree gets older, and certainly if you reach a point in which you are happy with its shape and size, you can reduce the amount of fertilizer that you use. Your bonsai tree will still need a regular dose of nutrients to remain vibrant and healthy, but it will no longer need growth stimulation.
By applying fertilizer cautiously and always potting your bonsai trees in appropriate bonsai soil, you can ensure that the right concentration of essential elements is always available when needed.
Signs That You Should Stop Fertilizing Your Bonsai Tree
While a healthy, growing bonsai tree will always be grateful to receive a timely dose of nutrients, moments may arise in which it becomes sensible to pause fertilization for a little while.
If your tree has become sick or is stressed in any way, then now is not the time to fertilize. Indications of stress include signs of infection or disease such as dying leaves. However, stress can also simply be caused by routine repotting of your bonsai tree or incidences of underwatering. A thirsty bonsai tree should never be fertilized—you should always water first to ensure that root burn isn’t a risk.
Warning signs that you may have over-fertilized your bonsai tree are very similar to those that indicate poor health, such as unseasonal yellowing or dropping foliage and an unexpected slowing of growth.
Another red flag is the visible build-up of fertilizer residue on topsoil. This can, once again, be a common problem if the wrong type of soil is used. If you notice this or suspect over-feeding, remove as much of the residue as you can and flush your bonsai tree’s roots with water to eliminate any damaging fertilizer build up. Then, skip the next scheduled fertilization or two to give your bonsai tree a chance to bounce back.
Fertilizing Bonsai Trees as Part Of Your Bonsai Care Routine
So many facets of bonsai tree care call for making observation a daily ritual. When approached with the right mindset, tending to your bonsai trees—whether watering, misting, pruning, or training—can become a meditative practice that always offers spiritual reward. Fertilizing bonsai trees is an important component of this delicate art form, so proceed with care and attention, so that you can watch the fruits of your labor slowly and gracefully emerge!