It is of vital importance that you fertilize your Bonsai tree. Since bonsai trees are usually confined to a pot, they can’t spread out their roots in search for moisture and nutrients like a normal tree. It will be up to you to provide all of the nutrients it needs. These nutrients are required to turn carbon dioxide and water into food for your bonsai. For this reason, it is important that you use a good quality fertilizer to top up the nutrients in the soil as they diminish. The nutrition of your bonsai is paramount to its good health.
What to Look for in Fertilizer
Fertilizer is a natural or synthetic material, made up of beneficial vitamins and minerals. When added to soil it will enhance the growth of the bonsai tree. There are three main nutrients in fertilizer: Nitrogen, Potassium, and Phosphorus. These will be represented on fertilizer packaging with 3 numbers representing the percentage of these three elements.
Nitrogen (N)
Nitrogen is the most important element for bonsai trees. Mainly because it is necessary for leaf development. It helps form protein, which your plant will die without. Healthy amounts of nitrogen result in strong branch development.
Think about how green the grass is after it rains. This is due to nitrogen in the rain drops.
Potassium (K)
Potassium is the second most important nutrient. It is extremely necessary for disease resistance and encourages sap flow and is needed for proper growth. Potassium can increase you bonsai trees stress resistance level by the activation of certain enzymes within the plant’s cells.
Phosphorus (P)
Phosphorus encourages healthy roots, helps flowers to prosper and provides energy. I recommend using a balanced fertilizer all year round and simply reducing the quantity after the growth season ends. The exceptions would be for a much older bonsai tree or deciduous bonsais during the winter; in these cases it is advisable to buy a fertilizer with lower nitrogen levels in its composition.
These are your 3 Macro-nutrients, and all you really need to know about, but if you want to delve further, check out The Fertilizer Institute. There’s a lot of great info there on secondary nutrients and micro-nutrients.
How Often Should You Fertilize Your Bonsai?
Fertilizing should take place from early spring until autumn. Bonsai trees go through a slow growth phase during this time. This is also when the extra nutrients, that the fertilizer provides, become most crucial to the health of your bonsai. You should fertilize indoor bonsai throughout the year. It’s also important to take into consideration the type of tree you have. Let’s talk about the major categories and their fertilization needs.
Fertilizing Tropical Bonsai
Only fertilize tropical bonsai on a weekly basis, between spring and Autumn. You can continue to fertilize them int eh winter months too, but their growth may slow during this time. If it does, then cut back to the fertilizing to every 3-4 weeks.
Fertilizing Coniferous Bonsai
These bonsai should be fertilized weekly during growth season so spring to autumn. During the winter fertilize monthly but use a reduced quantity of fertilizer.
Fertilizing Deciduous Bonsai
You should fertilize deciduous bonsai every two weeks during the growth phase. Some enthusiasts find it unnecessary to fertilize during the winter months, whilst others may fertilize monthly using a fertilizer with 0 nitrogen content. So, using for example a 0-10-10 fertilizer.
It is important to try to find the correct balance of fertilizing for your bonsai. If you get the balance right and avoid over or under fertilizing, your bonsai will thrive with shiny bright leaves!
What Kind of Fertilizer Should You Use?
Given that many bonsai substrates are not really composed of soil, using a fertilizer containing trace elements, such as calcium, Iron, magnesium and nickel, is also advisable. Check the packaging to see if the brand you are using contains these.
Most people choose to use both organic and inorganic fertilizer, varying between the two. Let’s break down these two types:
Organic Fertilizer
Organic fertilizers are not processed. They only contain animal or plant-based components. The elements, including nitrogen, are released slowly. This eliminates the risk of burning the roots by accidentally over fertilizing. Organic fertilizers are beneficial to the soil in the long term and can provide it with important microbes. On the downside it may not contain all the trace elements that are helpful for your bonsai that will be found in many inorganic fertilizers, they can also have a strong odor.
Inorganic Fertilizer
Inorganic fertilizers are synthetic. They will release the three main elements quickly; they will therefore quickly transport into the plant providing it with all the essentials to grow well. Inorganic fertilizer can cause a buildup of salt in the soil overtime which is undesirable as it can cause damage to your bonsai. It is the optimum choice if your bonsai tree needs quick fertilization. It is important when using inorganic fertilizer to follow the guidelines carefully as it is possible to over fertilize. This is detrimental to your bonsai tree. For certain species such as azaleas over fertilizing can result in the bonsai dying.
Liquid vs Solid Fertilizer
Fertilizers come in either liquid or solid form. This is mainly a matter of preference. Solid fertilizers, like pellets, will break down slower. The soil will absorb the nutrients every time you water your bonsai. You can mix the fertilizer a little with the substrate or, in the case of fertilizer pellets or cakes, you can cover them with cup shaped mesh. Water the soil after placing the fertilizer. Make sure to place some towards the edges of the pot to entice the roots to grow outwards.
Liquid fertilizer also has its benefits, one being better coverage. Before you apply the liquid fertilizer, make sure the soil is wet.
Again, in recent years many enthusiasts have chosen to use a combination of both with good success. The most important thing is that once you have picked a fertilizer you read the instructions carefully and follow the guidelines given.
Don’t Over Fertilize!
Luckily, there are some ways to tell that your bonsai is being over fertilized. The tree will display certain signs. Always be on the lookout for a crusty layer of fertilizer on top of the soil. Leave may begin to yellow and develop brown tips. These will usually begin wilting lower on the tree. Also, slow growth or leaves that drop too early can be a sign.
Make sure to avoid avoided fertilizing your bonsai for about 1 month after repotting! For more info on repotting, check out our bonsai repotting guide.