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Bonsai Fertilizer FAQ's

If you are new to bonsai gardening, fertilization can be confusing and perhaps even intimidating. We are here to help with answers to the most frequently asked questions related to feeding and fertilizing your bonsai. 

Please note these are answers to general questions about fertilization. They should not substitute for any care guide you received with the purchase of your bonsai, or the labels or instructions that accompany the fertilizer you choose to use.

When should you fertilize a bonsai?

Because bonsai trees are cultivated in limited amounts of soil, regular feeding is important. During the growing season (early spring through late summer) your bonsai should be fed weekly with bonsai fertilizer. Keep in mind that your bonsai may stop absorbing nutrients during late summer and early fall. As growth begins to slow you should reduce your fertilizing schedule to only once a month. Here are some guidelines for specific classed of bonsai.

  • Deciduous bonsai trees should be fertilized weekly during the growing season and stopped once the leaves have fallen. During the fall and winter months feed your bonsai a 0-10-10 fertilizer. Read more about the benefits of zero nitrogen fertilizers.
  • Conifers should be fertilized weekly during the growing season. They will also benefit from being fertilized a few times during the winter. For the fall and winter months feed your bonsai a 0-10-10 fertilizer. Read more about the benefits of zero nitrogen fertilizers.
  • Tropical and sub-tropical bonsai should be fertilized weekly during the growing season. They will continue to grow throughout the year and should be fed on a monthly basis from fall to spring.

In any case, don't starve your bonsai. Regular fertilizing will help keep a bonsai small and prevent the plant from getting spindly. But remember: never feed a sick bonsai, only feed healthy trees!

What type of fertilizer is best for my bonsai?

The best fertilizer is a bonsai fertilizer specifically formulated to provide an optimum level of salt in the soil solution when used as directed. Let us explain what that means.

Fertilizer is simply an alternate source of all the basic nutrients, such as nitrogen, phosphorous, potassium, and trace minerals that exist naturally in a healthy soil. Fertilizer feeds the soil, not the bonsai. Fertilizer breaks down in the soil, either by being dissolved in water or by microbial action, releasing its nutrients in a form that plant roots can absorb. Plants use nitrogen for leaf production, phosphorus for root and flower production, and potassium for flower production and general vigor. General purpose fertilizers are typically balanced. They contain all three major nutrients which are present in the proportions likely to be found in a healthy soil. These general purpose fertilizers are suitable for use on lawns, trees, shrubs, flowers, even vegetable gardens where there are no special problems with the soil.

Special purpose fertilizers are typically "unbalanced" featuring a greater proportion of one or the other major nutrients or special trace minerals or enzymes that suit them for particular situations or bonsai. For instance, there are bonsai fertilizers labeled for acid-loving plants such as azaleas that help provide iron in a form that these plants can use. Let the directions on the fertilizer be your guide and, when possible, use a specialized bonsai fertilizer to maintain its health. 

What is NPK on fertilizer labels?

Don't be intimidated by the three-number code on bags of fertilizer. It indicates the levels of nitrogen (N), phosphorus (P), and potassium (K) in the fertilizer. Nitrogen is responsible for the intensity of the color green in the plant. Phosphorous is good for maintaining the root system as well as the plant's blooming and fruiting. Potassium is necessary for the general vitality of the plant. You can read our article for more information about NPK.

What's the difference between liquid fertilizers and granular (pellets)?

Fertilizer is available in two types: liquid and granular. Choose the one that meets your needs in the form that is easiest for you to use.

Liquid fertilizers are fast-acting and quickly absorbed. However, liquid fertilizers require more applications. Every time you water your bonsai, your washing away the fertilizer you previously applied. Granular fertilizers are applied dry and must be watered in. Granular fertilizers are easier to control because you can actually see how much fertilizer you are using and where it is being dispersed. Both fertilizer types are appropriate for bonsai gardeners, and most bonsai gardeners will use both types of fertilizer for maximum balance. 

Is there an advantage to using organic fertilizer?

The major elements needed for your bonsai are N, P, and K. The source doesn't matter to the plant. The salts will ultimately be employed by the bonsai in exactly the same fashion. The major benefit of organic fertilizer is that it releases nitrogen slowly and it is less likely to burn the roots of the bonsai if you accidentally over-fertilize. Some fertilizers, such as chicken manure or liquid fishmeal, have a distinct odor, so you may not want to use them on indoor bonsai. However, not all organic fertilizer will smell bad.

Also, organic fertilizers do not always contain all of the trace elements and minerals your bonsai needs. Therefore, you may need to apply several different organic fertilizers or apply them more frequently to compensate. It may be a good idea to alternate fertilizers (organic and non-organic) from time to time in order to give your bonsai a mixture of trace elements.

No matter which fertilizer you choose, the most important thing is to follow the directions on the package. Using too much fertilizer or using it too frequently increases the risk of damage to your bonsai.

Are there times when I should avoid fertilizing my bonsai?

Yes. Probably the most important rule about fertilizing is to never feed a tree that is under stress. You should never feed a newly repotted tree, a dry tree, or a tree during dormancy. After repotting, leave the bonsai alone for at least a month before starting feeding again.

Am I wasting my money using SuperThrive or other organic vitamins?

SuperThrive is very controversial. Asking gardeners what soil mixture is best for your bonsai will likely get you several different answers, and the same is true of SuperThrive.

Many bonsai gardeners swear by SuperThrive, saying it makes a big difference in their plants. But it seems that almost as many say it makes no difference and is a waste of money. If you read SuperThrive's brochure or container, you will find they guarantee the product will do everything in the world: 60 years unchallenged, #1 grower, #1 activator, #1 transplanter, and so on. However, they do not include a list of ingredients, only touting 50 vitamins and hormones.

If you decide to use the product, we recommend you follow the mixing instructions of 1 drop per gallon since we don't know the ingredients. SuperThrive is not a fertilizer; therefore you may use it in addition to (but not instead of) ordinary fertilizers or plant food. SuperThrive contains 50+ vitamins and hormones that will help all your plants, including orchids, grow to their fullest potential. It has been around for decades, and nurseries and other professional growers swear by it. It's also one of our best sellers. Use it with your bonsai, house plants, and vegetable gardens.

Should I add trace elements to my bonsai soil?

A healthy bonsai begins with the soil. All organic matter contains various levels of trace elements, and it is often found in the form of soil or fertilizer . But the levels in soil and fertilizer are not sufficient for long-term growth. Bonsai soil in particular cannot supply enough of the vital trace elements that are needed.

But there are products available such as FRIT that can help fill the trace element void. FRIT contains more than 28 trace elements and minerals on the major and minor scale that are essential to the health of your bonsai tree and other houseplants. It is a dual-acting compound that releases these major trace elements over a 12-month period. Because 30 percent of the compound is soluble in the first hour following application to the soil, your bonsai gets an immediate infusion of needed trace elements. This ensures an instant remedy for trace element inadequacy. The remaining 70 percent of the compound is released slowly and evenly over the course of a year in order to maintain your bonsai's health.

DISCLAIMER: The content provided in this article is not warranted or guaranteed by Bonsai Outlet. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. Happy bonsai gardening.