Article written by Gary English and published on this website with kind permission of The Gardener magazine.
© Gary English gary@cybersmith.co.za
© The Gardener Magazine - Editor: Tanya Visser tanya@thegardener.co.za
Fertilizing - Part 2
Fertilizing Bonsai is very important because they are planted in (to) small pots, with few feeding substances. Fertilizing regular and in the right manner ensures a healthy and controlled growth.
Parts of fertilizer
All fertilizers provide a NPK value, which is very important for using the right type of fertilizer in the right season. N is chemical denomination for nitrogenous, P for phosphorus and K for potassium, these substances have special functions which will be used for Bonsai. There are also substances such as sulfur and calcium which have there own functioning/s. For Bonsai especially the NPK value is important.
(Nitrogenous) = General growth of the tree.
(Phosphorus) = Promotes the development of buds and fruits.
(Potassium) = Very important for making trees hardy for the winter.
As you can see, N is important for growth, and K for stopping growth, in order to make a tree ready for the winter season. During the early spring season a fertilizer with a high N value needs to be selected. During the late summer and autumn a fertilizer with a high K value needs to be chosen. So using a special 'Bonsai fertilizer' isn't necessary, the only thing that is important is chosing a fertilizer with the right NPK values! Some Bonsai shops sell special fertilizers for the spring and for autumn, which can be useful.
When to fertilize
Normally fertilizing can be done from the early spring season untill autumn. Firm fertilizers can be applied up to twice a month, liquid fertilizer once a week. Best is to use firm firtilizer for the ground, and liquid fertilizer for the leaves.
How to fertilize
Fertilize Bonsai with half of the recommended quantity of fertilizer for normal plants. A tree must not be fertilized until two months after it was repotted. Young trees who will be formed can be fertilized more, or more often. Use the right NPK value of fertilizer in the right time of year.
In the early spring and summer Bonsai have to be fertilized with a firtilizer with a high N value, to stimulate the growth. Choose a value of about 15-10-5 (N-P-K). Already formed trees can be fertilized with less Nitrogenous: 5-10-5 (N-P-K).
During the late summer and autumn the growth have to be stopped to stimulate the growth of buds, to survive the winter season. Choose a fertilizer with a low N value, and a high K value, like 5-5-25.
Leaf fertilizing
You can solve liquid fertilizer in water (use half of the recommended quantity of fertilizer for houseplants) and spray this on the leaves of a tree to relieve the root system, and so strenghten the tree. The leaves will grow bigger, so only do this with trees who are still in training.