In nature, trees are able to gather nutrients from deep within the earth. As a tree in a pot, the bonsai is dependant on us for the nutrients and minerals they need to thrive. Knowing when, how much, and how often to fertilise your bonsai tree is very important. There are two ways to fertilise your bonsai tree. With liquid fertiliser, and with slow release pellets. Both contain similar nutrients. It is recommended that you use both to cover a broad range of nutrients and minerals
When Do I Fertilise?
Indoor bonsai varieties can be fed low amounts of fertiliser year-round. Most likely, though, you will own an outdoor bonsai tree. Outdoor bonsai trees can be split into two categories. Deciduous and Evergreen. Deciduous trees lose their leaves in autumn and they grow back in spring. Evergreen trees keep their leaves year round (for the most part). Deciduous bonsai should fed from early spring to early autumn. Evergreen bonsai should be fed from early spring to late autumn. Deciduous tree feeding ends earlier as they go dormant and stop feeding for the most part.
How Much Do I Fertilise?
There are many bonsai fertilisers out there, but the below products will definitely do the trick. A good fertiliser for bonsai has a balanced NPK rating. NPK stands for nitrogen (N), phosphorus (P) and potassium (K). These are essential plant nutrients. A fertiliser will also contain trace elements and minerals. When fertilising, we recommend using half the recommended amount of fertiliser. The bottom of this guide explains the process in detail.
How Often Do I Fertilise?
- Liquid fertilise every two weeks using a balanced fertiliser such as 'Nitrosol' (liquid blood & bone) or you can use ‘McGregors Vege & Ornamental’ if you are animal conscious like us
- Apply liquid seaweed tonic every other month for plant health. You can mix this in with your Nitrosol or VegeMax feed.
- Apply a teaspoon of Tui container feed at the start of spring
- For acid loving trees, sprinkle a teaspoon of acid food onto the surface of your bonsai after flowering finishes. Water gently as it dissolves.
What Do I Fertiliser With?
Trees don't care where their nutrients come from as long as they're receiving enough of them. Below are some examples of suitable fertilisers that can be found at Mitre10 (Nitrosol, Container Feed, Acid Feed) or Countdown (Vegemax).
The Fertilising Process
Always follow the directions on the fertiliser package, and water the bonsai thoroughly before feeding to avoid root burn. Bonsai trees like to be 'primed' with water before up-taking nutrients. Do not fertilise if the tree is diseased. Do not fertilise newly re-potted trees for at least a few weeks.
A note on flowering bonsai trees: Don't feed flowering bonsai while they flower, otherwise they'll direct that energy into leaf growth. If your bonsai has too few leaves and is trying to flower, then remove the flower buds so energy goes towards new leaves (this only applies to evergreen flowering trees, as deciduous flowering trees will flower before producing leaves). Leaves are more important than flowers because with little or no leaves, there will be no future flowers.
Start by pouring the required amount of fertiliser into a watering can. You will need a watering can with a rose head (around 9 or 10 litres) to dilute the fertiliser in water. For liquid fertiliser, I dilute 20ml in 9 L of water. If I am applying my seaweed tonic and the same time, then I also pour 30ml into the same watering can. We watered our bonsai prior to this, so we can go ahead and fertilise now. Make sure to get the foliage too as the leaves can always uptake nutrients. Repeat in 1 minute. Fertilise again in 2 weeks until the end of your tree's growing season.
If your goal is to achieve smaller leaf size on your bonsai then reduce the fertiliser amount by half. While this reduces leaf size, it will also mean your bonsai is not growing at a vigorous rate. After reducing feeding for a year, it is advised to fed at a normal rate in the following year.