How to fertilize bonsai
There are two kinds of fertilizer:
- Organic fertilizers with a deferred action that's slower
- Chemical fertilizers are immediately absorbed by the tree
It is better to use organic fertilization, since it's less dangerous. Their action is more durable, softer. Furthermore, they improve the holding capacity of nutritive elements in the substrata, make it more flexible, increasing its biological activity.
Indeed organic fertilizers are not absorbed by the rootlets just as they are. They must initially undergo a microbial degradation. This produces humid acids that, once degradation is complete, will be absorbed.
Therefore, you see that it is imperative to have a microbial flora in the soil. This flora arrives by itself, but you can introduce it by adding humus-producing substances - either in liquid form or as solids in the form of well-decomposed composts. You can use them by covering the soil mix with them, or by mixing them with water (3 parts to 7 of water) and sprinkling over the surface before adding organic fertilizer pellets.
You will understand that this fertilization will acidify the soil. It will therefore have to be neutralized from time to time - in late spring and also as autumn finishes (see diagram opposite). For good organic fertilization you can use pellets of fish or meat meal and soya bean oil cake used in the proportions of 2 - 8 to 3 - 7. In spring it is necessary to force on the animal flours.
Chemical fertilizers are much faster, sometimes instantaneous, but they burn and impoverish the soil mix.
You can use them, but just in quite specific cases when, for example, you want to accelerate growth. It's always necessary to sprinkle this type of fertilizer to avoid burning the roots.
At nurseries and garden centers, you will find an impressive array of pellets adapted for every season - even for individual species of tree. Go and take a look, but remember that trees need three specific elements.
N = Nitrogen: the growth promoter. Young trees need this in great quantities in the spring, and then in very limited amounts until autumn.
P = Phosphorus: promotes the growth of roots.
K = Potassium: Promotes resistance of the tree which makes it possible to accumulate reserves. Useful for flowering and fruiting..
Calcium, magnesium and iron are also useful, as are the trace elements (cobalt, manganese, sulfur etc.).
Note The substrates such as Akadama, red grit, and pumice are often sterile. It is therefore obligatory to fertilize. Even a substratum containing compost requires fertilizing because, thanks to watering, it quickly becomes impoverished.
Neutralize the soil
1 part of wood ash to 9 parts of water. Allow to settle and then sprinkle
To neutralize the soil medium sprinkle with the ash and water mixture.
The more you fertilize, the more the medium is acidified. A very acid medium slows down the assimilation of the fertilizer. Therefore, it should be neutralized both at the end of spring and of autumn to re balance it.
When to fertilize
- In general, you can give more nitrogen in spring, and more phosphorus and potassium in autumn
- Fertilization must be adapted according to the season and the stage of cultivation the trees have reached.
- Do not fertilize in winter because the trees are in dormancy and their rootlets won't absorb fertilizer.
- Indoor bonsai can be fertilized more or less all the year round.
- If you apply a chemical fertilizer, do not do so at the end of autumn because its over brutal action would make the plant suffer just before its dormancy.
- When you re-pot you can put in organic fertilizer in pellet form. It will degrade and be transformed into humic acid in 15 - 21 days. At this time, new rootlets will exist so don't risk anything more. In any case, don't apply chemical fertilisers. You can use the liquid organic fertilizer. In this case it should be used either once per week or every 15 days. Be careful with it.
- Do not fertilize sick bonsai or those receiving treatment.
Various kinds of fertilizer
There are many ready-to-use fertilizers available that are suitable for bonsai. Here are some examples, but it is best to ask your local bonsai nursery which fertiliser is best to use for your particular bonsai.
Super Bio Gold - a well known Japanese brand in the form of pellets. It comes in bags and cans as shown here. These can be diluted in water if you prefer a liquid fertiliser, which is less messy than pellets. Suitable for fertilising in spring.
Bio Vital - liquid fertiliser can be used for all bonsai.
Abrakas - Japanese pellets 9 are a slow release organic fertiliser that can be used for all bonsai during summer.
Rainbow liquid vitamins - not a fertiliser, but a liquid form of vitamins. It can be used for weak bonsai or just after repotting to help revitalisation.
PK Fertiliser - for resistance to for fungal attacks, to stimulate flower buds, or to help give bonsai a boost before winter.
Bio Green - is an organic liquid fertiliser. It stimulates healthy growth, resistance to diseases and improves the root system. It can be used for in- and outdoor bonsai.
Fish emulsion - Fisch emulsion is the most gentle acting of al bonsai food mixes. It help produce healty plants withe sturdy stems and strong root systems. it will also improves flower production and glossy foliage. Applicable as general fertiliser too.
Annual fertilisation schedule
|February||If necessary, spray on a prophylactic treatment of sulfur + copper.
Spray the trunks and branches with trace elements Ca; Fe; Cu (every 15 days).
|March||Spray the trunks and branches with trace elements Ca; Fe; Cu (every 15 days).
At the end of March, start organic fertilization.
- Young bonsai: fertilize with higher level of nitrogen (N higher than P and K).
- Mature Bonsai: either apply nothing at all, or a balanced and weak NPK (lower than 6).
|April||If you use organic fertilizer pellets, make sure they degrade well. It is necessary to change them as soon as they have disintegrated. Adopt the same principle of fertilization as described above. The more you use pellets, the more it's necessary to water.
You can always spray solutions of trace elements on the foliage, once a week.
|June||As April. At the end of the month neutralize the soil mix with water + ashes|
|July||If you water often, or if it rains, you can fertilize as in the spring, but in lesser amounts. Otherwise, remove the pellets, but spray the leaves with trace elements.|
|September||Autumn fertilization. P and K much higher than N (which can remain present, or not). It's necessary to continue fertilising while the plant is still active, and so long as leaves remain. At the end of month neutralise the soil mix with water + ashes.|
|October||Ditto, except for neutralization|
|November||Ditto, except for neutralization|
|December||Nothing, except perhaps spraying a sulfur + copper treatment, if necessary.|