Bonsai Fertilizer Explained: Let’s talk about N-P-K and Why it Matters

Let’s talk about N-P-K and what they mean and how it applies to bonsai fertilizer.

What the Letters Stand For:

There are three nutrients present in fertilizer with each one serving a different function for the tree.   These nutrients are essential to all plants. However, when considering their use for bonsai, we have to take into account other considerations as illustrated below.

  • Nitrogen – used to promote the health of leaves or foliage on your  tree. Too little and your leaves may grow too small and weak. Too much and you run the risk of burning the leaves.
  • Phosphorus – Promotes healthy root growth, flowers, and fruit. Too little, and the tree will grow very slowly or not produce nice flowers or fruit.
  • Potassium – Helps with the overall plant function and vigor including boosting its resistance to pests and diseases.  

“There are three nutrients present in fertilizer with each one serving a different function for the bonsai tree. “

Numbers - An Easy Breakdown

The numbers that you see on the package indicates the proportion or percentage of the nutrients in the soil. This is represented as three numbers in the order of Nitrogen, Phosphorus, and Potassium.  N-P-K = Nitrogen-Phosphorus-Potassium

Let’s take a 100 pound bag of 20-10-10  fertilizer and break it down. If you have a fertilizer that is 20-10-10, Nitrogen comprises 20% of the fertilizer. So in a 100 pound bag of fertilizer, 20 pounds of the fertilizer is nitrogen, 10 pounds of the bag is phosphorus, and 10 pounds of the bag is potassium. This would mean that 40% of the bag or 40 pounds of the 100 pounds of fertilizer contains one of the three nutrients.  

What about the Remaining Content?

So what is the remaining 60% of the bag.  The rest of the ingredients help safely disperse the chemicals into the soil and is typically comprised of inert material that does not contribute to the N-P-K proportions labeled on the bag.  However, soil amendments are sometimes used as well that can help aid your plant that may not contribute to the N-P-K label. 


Fertilizing can help your tree grow much quicker as well as help it protect itself from insects, pests, and diseases. Slow release granules work extremely well with Juniper bonsai. Once placed on your the topsoil of your tree, the granules will slowly dissolve with every watering. The fertilizer granules will break apart and provide nourishment to the tree’s roots over time.

Once the granules or tablets have dissolved you can add more to continue feeding your tree. We recommend feeding your tree from Spring to Fall, scaling back during the Winter. Follow the instructions for the fertilizer to prevent overfeeding and burning of foliage.   Over fertilized trees are at risk of burned leaves and possible death if used incorrectly.

How can you use their numbers?

Now that you know what the numbers mean and what each nutrient does for your plant, you can decide what type of fertilizer to use.  Fertilizers come in many different varieties with different proportions of N-P-K. Below are some different amounts used that you can find with explanations on the uses of them.  

  • 12-8-8 – A general composition that provides a more nitrogen to leaves and foliage. Can be helpful when leaves on your tree are slightly yellow.  Otherwise, it is well balanced for overall root health and plant vigor.(Gro Power Planting Tablets)
  • 3-12-6 – This composition is high in phosphorus and will benefit fruiting and flowering of the tree. This would be a good fertilizer to use for flowering plants to help promote vibrant flowers and blooms. (Dyna Gro Bloom)
  • 7-9-5 – This balanced mix focus more on the root growth, flowers, and fruit as well as foliage. A very commonly used fertilizer for bonsai. (Dyna Gro Bonsai Fertilizer)
  • 5-5-5 – A very balanced fertilizer that will give you equal parts of everything. Although it contains low proportions of N-P-K, other soil amendments in the remaining mix contribute to the overall health of the tree. This is common for organic fertilizer. (Dr. Earth Created for Life All Purpose Fertilizer)
  • 0-10-10 – An interesting composition or “incomplete” fertilizer that does not provide any Nitrogen.  During the winter dormancy, we’re concerned more with the overall root structure and resiliency of the tree rather than its foliage especially with deciduous trees. Leaving the nitrogen out will not force the leaves to grow at a time when it should be dormant.  (Ho Yoku Hy Nitrogen Free Bonsai Fertilizer)
  • 20-9-9 – This fertilizer will promote strong leaf and foliage growth. However, if used too much may lead to leggier growth or possibly burn the foliage.  (20-9-9 Bonsai Fertilizer)

As you can see, you can choose a fertilizer that will accomplish your goals for your tree the best. If you know that your soil mix or tree already has a certain nutrient, you can use an incomplete fertilizer or one that is missing one of the components of nitrogen, phosphorus, or potassium.


Liquid vs Slow Release Granules

When it comes to choosing a type of fertilizer, there are lots of choices and brands but one of the most discussed topics with fertilizer is whether to go with liquid or to go with granule fertilizer.    

Granule fertilizer is extremely easy to use and does not require any mixing. Simply add it to the top of your bonsai tree and it will start to work. Some granules require UV rays to break down the shell so make sure you follow the instructions to see how to use your bonsai fertilizer. One thing that’s great about a granule fertilizer is that it’s usually slow release, meaning as you water your tree daily, it will slowly dissolve into the soil. This is a great option for people that like to see if their fertilizer is being used and it makes it visually easy to see if the fertilize needs to be replaced. For beginners, we always recommend granule fertilizers. Even on professional show level trees, a slow release fertilizer is used.    

Liquid fertilizer is a little bit more cumbersome to work with. However, if you follow the instructions, you’ll be able to mix a good amount easily. Usually one concentrated dose of about a tsp on most brands will yield about 2 gallons. Follow the directions on your fertilizer. The biggest benefit of using a liquid fertilizer is how quickly it gets absorbed by the tree. This will give you fast and instant results as opposed to granule fertilizer. The downside is that it can get washed away through watering. If you are using a quick draining soil mix, your fertilizer can wash away after a few waterings.    

For Beginners

For beginners, the easiest is to use a balanced mix of Nitrogen, Phosphorus, and Potassium.  The overall goal for beginners is to have any overall healthy tree. Once you’re able to do this, you can experiment with fertilizers to accomplish different goals.

The overall goal for beginners is to have any overall healthy tree. Once you’re able to do this, you can experiment with fertilizers to accomplish different goals. “

Back to the Balance

Now that you understand fertilizer a bit better, you’ll see how balancing the fertilizer is important.  Fertilizer can be both positive and detrimental to your tree if used incorrectly. Take care to follow the instructions as labeled on the packaging.  Experiment and see what works best for your tree and circumstance. 

Like this article?