Bonsai Fertilizer

Nourishment for Your Bonsai Trees and Plants


Bonsai fertilizer is a vital element in promoting growth and maintaining the health and beauty of your tree.

Plants use nutrients from the soil to make their food. Trees planted in the ground and growing in their natural habitat are able to search for nourishment by spreading their roots out to surrounding areas. Also, organic matter decomposing on forest floors or in outdoor environments will replenish soil and provide the essential chemicals that plants need to survive.

Bonsai, however, are confined to very small containers with little soil. Once the plant has used the nutrients immediately available, it has no way of branching out to search for more. This is why it is necessary to fertilize regularly. Fertilization replenishes depleted bonsai mix and gives your plant the nutrients required for health and growth.

Your bonsai needs three essential elements: Nitrogen (N), Phosphorus (P), and Potassium (K). These chemicals are needed in fairly large quantities for your plant to grow and develop properly. They will be listed on your bonsai fertilizer package as a ratio N:P:K. For example, a balanced ratio would be indicated as 10:10:10, whereas a nitrogen heavy fertilizer would have a ratio of 10:5:5. Ratios indicate relative proportions, so 10:10:10 is the same mixture proportionately as 5:5:5 or 15:15:15.

  • Nitrogen: This is the first number listed in the ratio. Nitrogen stimulates the growth of leaves and stems and give foliage its green color.

  • Phosphorus: This is the second number listed in the ratio, and is usually in the form of phosphates. Phosphorus is responsible for healthy root growth.

  • Potassium: This will be the third number of the ratio. Potassium will typically be listed as Potash, and aids in the production of fruit and flowers, cell regeneration, and winter adaptation.

The type, or ratio, of fertilizer needed will depend on a number of factors including the species of bonsai, the age of the tree, the time of year, and the growing conditions. It is important that the fertilizer have the correct nutritional balance or mixture for maintaining the optimal health of your plant.


When to Fertilize

You will need to fertilize your bonsai throughout the entire growing season, usually from early Spring until mid-Autumn. Most outdoor bonsai should not be fertilized in the Winter since this will encourage growth that should not occur because the tree is supposed to be in dormancy. Exposing new leaves and shoots to cold and frost can cause severe damage to the plant.

Indoor bonsai can be fertilized regularly all year round.

Using different fertilizers will give you more control over your bonsai's growth and development.

Many bonsai growers apply a bonsai fertilizer that is high in Nitrogen during the early Spring to promote leaf and shoot growth. Look for one with a ratio of about 10N:5P:5K, but do not use this mixture throughout the entire growing season, as growth will be too rapid and the tree will require much pruning to maintain its shape and style.

Once the tree has come out of dormancy and initial growth has been encouraged, it is recommended that you use a balanced fertilizer throughout the Summer months, with a NPK ratio of 10:10:10.

One of the main roles of Potassium is to prepare the plant for Winter. During early Autumn, switch to a fertilizer that is lower in Nitrogen and higher in Phosphorus and Potassium, which will slow or inhibit growth so the tree can enter into its dormant stage. A mixture of 3N:10P:10K will help strengthen the leaves and root system so that the plant can withstand colder temperatures.

Although these are the general guidelines typically followed, there are exceptions. For example, if you want to encourage your tree to flower, you will need to use a bonsai fertilizer with a high Potash, or Potassium content. However, it is important to note that increased flower production could come at the expense of leaf and shot growth, since your plant will be receiving less Nitrogen.

If you have an older tree that is already styled, you may want to use a balanced fertilizer or one with a slightly lower Nitrogen content throughout the entire growing season, since you are not really wanting to stimulate vigorous Springtime growth.


Types of Bonsai Fertilizer

Basically, bonsai fertilizer is regular plant fertilizer. In other words, they don't contain any special or secret ingredient meant specifically for bonsai. As long as the fertilizer has the appropriate NPK balance or ratio, any kind is fine. However, many growers prefer to buy from a bonsai shop or website since they are sure to get the right balance for their species of tree, age of plant, and time of year.

Bonsai fertilizer can be purchased in either solid or liquid form. Solid fertilizer is usually granules, pellets, or powder, and is planted into the top of the soil below surface. It will slowly dissolve over time as the plant is watered. For outdoor bonsai, it is recommended that you use a fertilizer cover or basket to make sure that the pellets or granules stay in place, and are not washed away or stolen by birds or animals.

Liquid fertilizer is usually sold as a concentrate and must be diluted before application. You will need to mix the fertilizer with water and then pour it onto moistened soil.

Many growers prefer solid fertilizers because they provide the tree with a steady and continual supply of nutrients and only have to be replaced every couple of months. However, they have a tendency to attract maggots and other pests, can have an offensive odor, and may affect the overall aesthetic appeal of your tree since they are often visible.

Solid fertilizers also give you better control of the amount being added, whereas liquid types can be difficult to mix or dilute, increasing the likelihood of over fertilizing. Some growers choose the liquid form because it acts immediately. Even though its effect is short lived and you will need to fertilize more frequently, it will give your plant an immediate boost, particularly when it is just coming out of dormancy or if the leaves begin to loose their bright lustre and need extra nutrients.

In most cases, you will need to reapply liquid fertilizer about every two weeks. If your tree is no longer in training, once a month may be sufficient. Pour the mixture over the soil surface until the plant is saturated and the surplus runs out the drainage holes. Fertilizer may be applied according to package recommendations, and using half strength is not necessary.

Some people also like to apply fertilizer to the bonsai leaves. The majority of a plant's nourishment is absorbed through the roots, but some nutrients can also be received through the foliage. Simply mix liquid fertilizer according to the package directions and then use a spray bottle to lightly mist leaves.


Bonsai Fertilizing Tips

  • Never over fertilize your bonsai, as this can burn or damage the roots. If in doubt, it is better to under fertilize.

  • Do not fertilize a plant during its dormant season.

  • Do not fertilize a sick plant. Dormant or sick plants will not consume enough nutrients, and the nitrogen will remain in the soil, causing salt levels to increase.

  • Check the fertilizing needs of your species.

  • Do not fertilize re-potted plants for at least one month. Some people will dispute this recommendation, stating that the plant needs additional nutrients to recover and repair from the transplanting; however, it is possible to burn the roots. The best thing to do is check out the suggestions for your particular species, or watch your plant carefully. If the leaves lose their vibrancy, you may consider a low nitrogen fertilizer.

  • Choose the right type of fertilizer for the time of year.

  • Young trees will need more frequent fertilizing, while trees no longer in training will require less, since you will want to maintain growth rather than encourage new development.

  • Always water before fertilizing. Never apply fertilizer to dry soil.

Bonsai fertilizer is important to the health and beauty of your tree. Knowing when and how to fertilize will allow you to nourish your plant and give it the nutrients it needs to thrive and grow.


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