Fertilizing your bonsai tree is an important step to ensure your tree has all of the nutrients it needs to grow and and thrive in its container. Unlike trees grown in the ground that can push their roots far out into the soil to search for more nutrients, bonsai trees are obviously confined and rely solely on fertilizer to replenish the soil with the nutrients required to keep the bonsai healthy and growing.
There are 3 main macro-nutrients to any fertilizer you can find on the market: Nitrogen (N), Phosphorous (P), and Potassium (P). All 3 of these chemical elements are useful for the tree’s survival in different ways and play a major role in a bonsai’s ability to grow. The elements will be represented on the front or back of most commercially offered fertilizer packaging in the order of N:P:K. The basic points you need to remember when selecting the right fertilizer for your bonsai are:
- Nitrogen stimulates foliage growth. (above soil growth)
- Phosphorous helps produce strong root development. (Underground growth)
- Potassium aids the tree with the movement of water within the cellular system and promotes flowering and fruiting. (overall health)
What Time of Year to Fertilize?
You should fertilize your bonsai during the entire growing season (early spring- late summer). Though there are a few exceptions, this rule generally applies to all outdoor, growing bonsai.
Choosing A Fertilizer
There are so many fertilizer choices to choose from that it can easily overwhelm anyone trying to select the right one for their bonsai. While, we do not recommend any particular brand (because there are quite a few good ones out there!), we do recommend certain ratios of N:P:K for your bonsai. Generally speaking, it is an effective method to use a balanced ratio like 6:6:6, decreasing the amount of fertilizer applied to the tree towards the end of the growing season. This also keeps it pretty simple and reduces the risk of over fertilizing.
There are some who advocate using a mixture of 10:6:6 in the early growing season (early spring to early summer), switching to a balanced fertilizer 6:6:6 throughout the mid-growing season (early summer to mid-summer), finally switching to a 3:6:6 towards the end of the growing season (mid-summer to late summer). This method is also a great option.
Solid or Liquid?
Fertilizer can be purchased in both liquid and solid forms and most bonsai enthusiasts use both forms to maximize growth of their trees throughout the growing season.
Liquid fertilizer is mixed with water before it is applied to the tree. It is absorbed rapidly by the tree’s roots, though, it also has a tendency to wash away each time the tree is watered and must be applied frequently in order to effectively feed the tree. If it is not applied often, most of the fertilizer will ultimately be washed away the each time you water the tree. A primary risk with using liquid fertilizer is the potential to over fertilize and damage the bonsai. Unlike solid fertilizer, there are no visual indicators as to exactly how much has been applied and therefore careful attention is required when using liquid fertilizer. An easy solution is to dilute the fertilizer substantially apply each time you water the throughout the growing season.
Solid fertilizer comes in pellets and is applied directly to the top of the bonsai soil, releasing a little fertilizer each time the tree is watered. To prevent the fertilizer from washing off the soil, it is usually placed in nets or small baskets and secured to the soil with toothpicks. It easy to determine if the fertilizer needs to be replenished because each time you water, you can visually see how many of the pellets have dissolved. Also, it is fairly difficult to over fertilize your bonsai with solid fertilizer.