Among the vast majority of veteran gardeners, bonsai cultivation is considered to be the crème de la crème form of gardening. There is a reason why growing bonsai is considered to be an art form.
The ancient tradition, dating back to 500 BC, has vital religious, traditional, and cultural linkages with China and Japan and has been traced back centuries to Zen Buddhism. For many gardeners engaging in this honorable practice, the growing of bonsai trees signifies a way of life consisting of patience, wisdom, and beauty.
A bonsai can not be differentiated into a certain type of tree; it is the disciplined curation of all kinds of regular trees or indoor plants and shrubs in a miniature version that imitates a fully grown version of the genus. Albeit, one can not champion this, or any, art form in a day; it requires years of practice and passion.
To kickstart your bonsai journey, here you will find everything there is to know about fertilizing bonsai trees, with useful information that applies to everyone, from beginner bonsai gardeners to seasoned bonsai gardeners.
More specifically, you will learn about each type of fertilizer that brings its own unique flavor into the bonsai recipe, and how to choose the best fertilizer for bonsai.
Table of Contents
What is Bonsai?
Realistically, the concept of bonsai is not merely limited to gardening. It is an evergreen discourse that has taught mankind the crucial lesson of discipline through effort numerous centuries ago.
For manifold modern gardeners, bonsai is the crown jewel of gardening.
To perfectly minimize a fully grown tree into its miniature version is a simple yet apt description of this delicately elegant process. While some consider Bonsai unlucky in homes, we still love to keep them to spruce up indoor spaces.
Do Bonsai Trees Need Fertilizer?
Bonsai maintenance relies heavily on the time of year. During early spring to early summer, bonsai trees display optimal growth. To complement this growth, proper fertilization is essential for the bonsai to blossom and thrive during the growing season.
In fact, a bonsai tree requires relatively pronounced fertilizer attention compared to regular trees as its root system is restricted to a pot; hence, the pot’s limited soil must be replenished religiously for healthy growth through a balanced nutritional content.
For your convenience, here is a bonsai maintenance calendar formulated by professional gardeners.
Bonsai Fertilizer Calendar
| Season | Growth Rate |
| Early spring and early summer | Highest |
| Late summer | Dormant |
| Early fall to late fall | Stabilizes and fruit is produced |
| Winter months | Dormant |
What Nutrients are Essential for Growing Bonsai?
There are three essential nutrients, commonly called main nutrients, that are compulsory for growing bonsai; thus, they are always included in a balanced fertilizer: Nitrogen (N), Phosphorus (P), and Potassium (K). These main elements combine to create the NPK formula.
The Three Major Elements: Nitrogen (N), Potassium (K), and Phosphorus (P)
Each major element serves a distinct purpose pertaining to bonsai growth.
- Nitrogen specifically deals with growth above ground, meaning it is responsible for growing the foundational parts of a plant: stem and leaves.
- Potassium is responsible for reinforcing plant health in a comprehensive manner.
- Phosphorus focuses on achieving a healthy root system and root growth while also concentrating on fruit and flower production.
Pro gardener tip! Always use the same NPK ratio throughout the bonsai growth cycle!
Important Secondary Nutrients for Bonsai
Besides the NPK nutrients, there are other elements, called trace elements and trace minerals, that are also responsible for bonsai growth; hence, they are included in all fertilizer labels. They include:
- Iron
- Manganese
- Zinc
- Copper
A few other trace elements are present as well, but their relevance is negligible.
Different Types of Bonsai Fertilizer
There are numerous types of fertilizer, and choosing the best bonsai fertilizer comes down to personal preference. The following section will compare all fertilizer types, allowing you to make an informed decision on choosing the best fertilizer for yourself.
Pro gardener tip: Before choosing a fertilizer type, you should keep in mind the age of your bonsai and the soil type it grows in!
Liquid Fertilizer vs. Granular Fertilizers (Solid Fertilizer)
Granular fertilizers consist of a slow-release method, which provides coherent nourishment to the soil over a lengthy period of time: 4 to 5 months, on average. These solid fertilizers are extra convenient as they often require no watering. Usually dug into the soil, they do not leach out when watered.
Liquid fertilizers are far more rapid in delivering nutrients to the soil. Favorably, they do not disturb the soil’s PH level either. However, if used excessively, they can be overbearing for the soil, causing root burn. They do, however, provide pretty much instant results in the right cases.
Organic Fertilizer vs. Synthetic Fertilizer (Inorganic Fertilizer)
Organic fertilizers take a subtle approach to delivering nutrients to the soil, containing only natural ingredients, which helps in mitigating the risk of root burn. They specialize in the stimulation of natural soil microbes that help in converting the organic fertilizer into soluble nutrients that are consumed by the plant roots.
Although organic fertilizers possess high contents of micronutrients (trace elements), they have lower NPK content compared to synthetic fertilizers. Most veteran gardeners call an organic fertilizer: ‘special tree fertilizer,’ and use it for everything from bonsai to vegetable gardens.
Synthetic fertilizers, also known as chemical fertilizers, act more rapidly. Their accessibility is enormous as they come in a wide variety of forms: pellet, liquid, granule, etc. While synthetic fertilizers provide the plant a quick hit in terms of NPK value, deliverance, and greening, they have minimal connotations on soil enrichment. With such fertilizers, the risk of burning is also high if applied in massive quantities.
Slow-Release Fertilizer vs. Quick-Release Fertilizer
Slow-release formula fertilizers act subtly but consistently as they provide nutrients to the soil for a lengthy time frame of 2 months. Quick-release fertilizers, on the other hand, deliver a competent pump of nutrients to the soil, but they last for about 2 weeks.
Our recommendation for you is to check out Perfect Plants Bonsai Fertilizer Pellets, which is a well-reputed slow-release fertilizer brand that has been making recent headlines, with nearly 6,000 Amazon reviews and stellar reviews.
Best Fertilizer for Bonsai (How to Choose)
Choosing the best fertilizer for bonsai depends on your bonsai’s age and soil type. Older trees will require a totally different care regimen than younger trees. However, as a general rule of thumb, a 7:8:8 ratio of NPK is the best harmony of nutrients that is not too harsh or ineffective for the soil.
Nonetheless, the NPK ratio changes according to various circumstances. For instance, during summer, use a 10:6:6 fertilizer with high nitrogen content to facilitate plant growth. Subsequently, the nitrogen content falls as the seasons roll on, with late spring demanding a well-balanced 6:6:6 ratio and autumn a 3:6:6.
Another intriguing ratio consists of a 6:10:6 NPK configuration, which is ideal for amplifying flower production from a lofty phosphorus content.
Pro gardener tip: A bonsai tree requires twice the frequency of fertilization indicated on the label and half the fertilizing strength!
Different Fertilizers for Different Types of Bonsai Trees
Juniper Bonsai
You can opt for either of the following two ways for fertilizing your juniper bonsai: slow release fertilizer granules or organic liquid form fertilizer.
With the slow-release fertilizer approach, you can fertilize your bonsai soil on a monthly basis during the seasons of spring and fall. The slow-release granules, when combined with the topsoil, provide nourishment to the soil when you water your bonsai.
On the contrary, an organic liquid fertilizer, which may come in the form of fish emulsion, can be used every two weeks. Compared to the former approach, it is more effective, as the liquid gets absorbed almost instantly into the soil. However, the liquid washes away when you water your juniper bonsai.
During the growth season of spring, combine nitrogen with your fertilizer for immense growth results due to increased nitrogen content.
Pro gardener tip: Here are some key pointers to consider when fertilizing your juniper bonsai.
- Your juniper bonsai may look wilted and flimsy due to overwatering; or over-fertilizing.
- Dilute your fertilizer to half strength for optimal results.
- Juniper bonsai trees are not indoor bonsai plants; they require substantial sunlight; hence, they are suited to the outdoors.
- You should not fertilize the plant for at least one month after repotting.
- For best results, use slow-release granules.
Deciduous Bonsai Trees
There are two branches of outdoor bonsai plants: evergreen and deciduous bonsai trees. Since deciduous bonsai trees are in their dormancy period during winters, they need to be kept outdoors.
The following are a few types of deciduous bonfire trees:
- Elm
- Maple
- Gingko
These magnificent trees need to be watered almost on a daily basis if kept outdoors under direct sunlight, or at least whenever their soil appears dry.
Apart from winter, when growth stops, you should fertilize your pot on a monthly basis. Pro gardeners recommend using slow-release organic granules as they have significant longevity, usually lasting for a month without being washed away by watering. You will be watering your plant on a daily basis, so liquid organic fertilizers will wash away.
Spruce
Spruce belongs to the evergreen branch of outdoor bonsai trees. The unique bonsai tree is known for its exhibitive whorted shape, which branches in every direction you can think of. Spruce provides a northern touch to your bonsai collection due to its conical shape.
In terms of watering your spruce, you need to keep the soil moist, but not soaking wet. Interestingly, spruce is a rare type of bonsai tree, which benefits from leaf-feeding, achieving intriguingly mysterious dark green color leaves.
For best fertilization results, ensure that you use a solid organic fertilizer once in four months. If you prefer liquid organic fertilizers, spraying them once a week over your spruce is adequate.
Bonsai Tree Fertilizer Type Takeaways
Choosing the best fertilizer for your bonsai, you need to first identify your bonsai type, the quality and texture of the soil, and the current season.
From the three examples above, we see each bonsai tree has distinct fertilization requirements. Since spruce is a leaf-feeding species, its requirement for solid organic fertilizer is relatively less compared to juniper and deciduous bonsai trees, at once every four months.
But, with junipers and deciduous bonsai trees, such as elms and maples, you need solid organic fertilization once every month during the growing period, which lasts from spring to fall.
Most professional and veteran gardeners prefer solid organic fertilization over liquid because of its reliability and consistency. Although liquid organic fertilizers are quick to act and more effective in delivering nutrients, they are easily washed away during watering, causing frequent reapplication on a weekly basis that proves to be costly in the longer run.
How to Fertilize Bonsai
As of yet, there has been no discussion on the process of fertilizing your bonsai. What are the intricacies of fertilization one should keep in mind?
The pesky dos and don’ts, common mistakes, and all issues related to the process of fertilizing your bonsai will be thoroughly discussed in this section.
- Understand your bonsai type and its soil type.
- Select a solid organic fertilizer that has superior quality. Pro gardeners prefer quality fertilizers and efficient brands such as Biogold and Aoki.
- Read the instructions on your fertilizer bag.
- Place the fertilizer in a small porous basket to ensure your precious fertilizer is not devoured by the forces of nature.
- The basket will now be placed upside down onto the soil as its opening goes firmly into the soil, and its bottom protects the fertilizer from above.
- Usually, place three baskets filled with fertilizer on the soil surface.
- Monitor your fertilizing regime and plant. The results should be noted down.
- If your bonsai is thriving under this regime, stick to it.
For liquid organic fertilizers, you can follow the following fertilization process:
- Read the manufacturer’s instructions.
- Stick to regular scheduling when applying liquid fertilizer because it leaches out during watering.
- Apply your liquid fertilizer on a weekly basis by spraying the foliage until the fertilizer drips down to the soil.
When to Fertilize Bonsai
The growing season encompasses early spring through mid-fall. Young trees require consistent fertilization throughout the growing season, whereas mature trees are fertilized based on their growth stage, current season, and health condition. A few bonsai types also require intermittent fertilization during the dormant winter season.
For example, a deciduous bonsai tree does not require fertilization during its dormant season as its leaves have fallen. Albeit, coniferous bonsai types require a few fertilizer sessions during winters as well.
It all depends on the type of your bonsai. Consequently, a little research into your bonsai type and its requirements go a long way. It shouldn’t take a long time.
When Not to Fertilize Bonsai
An experienced gardener knows when to draw the line with fertilizer. You should hold off and let a stressed tree gather itself before fertilizing it.
To identify a stressed tree, look for discoloration of leaves, wilting, and leaves falling excessively.
A prime example of a stressed tree is one that has been recently repotted; experts advise not to fertilize a repotted tree for at least a month.
How to Test Your Soil for Nutrient Content
The soil surrounding a bonsai is critical to its survival as it forms the largest chunk of its ecosystem. Testing for the soil’s nutrient content is a valuable practice that leads to several inferences.
Not everyone at home can test for carbon dioxide excretion from their bonsai leaves to test for soil health, so here are three simple steps that you can recreate at home for testing your soil’s nutrient level.
- Earthworms are your best friends. While most bonsai growers choose to get rid of worms from their soil when they bring their plants indoors, they may have managed to hide well enough for you not to find them. Dig a 6-inch deep hole into the surface of the soil and look for earthworms. If you find at least 2, it is a sign that they have enough nutrients for regular feeding, resulting in healthy soil. Now, bonsai are restricted in this regard as they are potted. However, earthworms are a lovely companion to plants, so some growers choose to let them live in their potting soil. The most important thing to consider if you choose to include earthworms in your soil mix is that you must ensure they have plenty of new and decaying organic matter to feed on throughout their life cycle. Without the right amount of organic matter in your potting soil, earthworms will cease to survive.
- The more plant residue, the better. Using the previously dug 6-inch hole, look for plant residue in the form of decomposing plant parts, including leaves, organic matter, and fibers. If you find plant residue, it means soil microbes are at work, meaning decomposition is taking place, which is ideal for returning key nutrients back to the soil.
- Soil structure. Using the same dug hole’s soil sample, run an observation on the size of aggregate soil clumps. If they are round and retain shape with slight pressure applied, it means the soil is rich and healthy. Round aggregates allow favorable water movement and aeration.
If your soil is not home to any creepy crawlies and plant residue, it is expected to be low in its nutrient content. Pine bark is one way to introduce more organic matter into the soil, and decaying organic matter is considered the best plant food.
To counteract this case and ensure healthy plants, you should slightly increase the quantity of fertilization. For example, if you are using a liquid organic fertilizer, increase the number of sprays until your test results prove otherwise.
Common Problems with Bonzai Fertilization
Overfertilized Bonsai
Overfertilized bonsai can prove to disrupt your bonsai’s good health to a great extent. A few symptoms of using too much fertilizer include:
- Wilting yellow foliage
- A whitish layer of excess fertilizer accumulating on the topsoil
- Premature dropping of leaves
If these symptoms persist, make sure you remove the layer of excess fertilizer, dilute the soil with water, and wait for a month before resuming fertilization, at least.
Under-Fertilized Bonsai
An under-fertilized bonsai will show signs of poor growth, consisting of a meager stem and small leaves. It will also show no signs of flower production or leaf production. Basically, it will be on the verge of collapse. To increase leaf and root production, water your bonsai with the optimum level of salt.
The solution is simple: use a balanced fertilizer during the growing season to attain healthy trees, especially with outdoor plants.
Other Frequently Asked Questions About Bonsai Gardening
Why is My Bonsai Tree Losing its Leaves?
Typically, a bonsai loses its leaves when it is unable to receive its required amount of sunlight. Most bonsai types are outdoor species, such as all deciduous bonsai types. These beauties adore sunlight, so if you are housing them indoors over the winter, be sure to consider an indoor grow light for your bonsai plant.
Another reason could be a lack of nitrogen in the soil; you can add a nitrogen spray to your fertilization routine for better results pertaining to the new growth of leaves.
Why is My Bonsai Tree Turning Brown?
The reason behind bonsai brownness is either a lack of watering or overwatering. Due to a lack of water, your bonsai will not be hydrated sufficiently to carry enough nutrients around its digestive system, while overwatering will cause root rot.
You need not use a gallon of water or a drop. A good idea is to find and strike the right watering balance, which can be challenging with indoor trees.
Why is My Bonsai Tree Not Growing?
The best way to encourage growth is to religiously fertilize your bonsai during the growing season. If your concerns surrounding growth persist, you can opt for a 10:6:6 fertilizer with greater nitrogen content.
Choosing the right fertilizer for growth requires nitrogen to be the MVP, as with almost any other normal tree. Either way, your bonsai health is dependent on a consortium of factors, so be mindful of all things at once.