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Bonsai for beginners, Issue #013-- Bonsai Feeding
March 12, 2008

Bonsai Feeding

What a summer, I don't remember such a long dry spell. We needed to buy in four tank loads of water between Christmas and the end of January. I'm sure a large percentage of which was sprinkled on my bonsai.

The Pohutukawa loved it though, I think the under watering during this period helped promote flowering on three of my trees. Dry conditions when buds are forming can often stimulate more flowers as the tree thinks it is going into drought conditions and it will go out of its way to create more flowers and seed to reproduce itself.

I don't advocate stressing your trees in this way unless you are about to have to hand over yet another $200 for a tanker load of water.

Flowering Pohutukawa

Close up of flowers

Close up of roots over rock

We have had quite a few questions from you all lately about feeding your bonsai - Should I? When should I? What should I? etc

So here it is.

Bonsai Feeding

Should I feed my Bonsai?

A tree that had been repotted and root pruned should be able to survive 12 months without feeding. You may however wish to boost growth or stimulate other characteristics of your tree. If you have an older tree that you do not repot each year feeding may be required.

When should I feed my Bonsai?

Firstly there are several times that you should not feed.

Don't feed directly after root pruning, wait at least 8 weeks - you may use a soil mix that includes a slow release fertilizer and it will do it no harm.

Don't feed sick or diseased plants. This is one of the most common mistakes I hear through emails. "My tree was sick so I loaded it with fertilizer to try and bring it back to health." It won't if your tree is diseased, it will not be taking up food and at best the fertilizer will be leached trough and wasted, or at worst it will build up and prevent water uptake compounding the trees problems.

Don't feed during heavy rain, our pots are only small with very good drainage and if you fertilize during rainy periods, liquid fertilizer especially will be leached out. Do water before by all means, about 25% moisture level is ideal.

Don't feed during hot weather, this is not quite so obvious but at high temperatures most trees will shut down and stop taking up nutrients. Around 20 degrees C or 68 degrees F are optimal temperature for absorption.

Do feed your trees during the growing season, usually spring and summer in most temperate climates.

What should I feed my bonsai?

Plant food is broken into two major groups; macro-nutrients and micro-nutrients. Most potting mixes will provide your trees with enough of the micro-nutrients so you shouldn't need to add any. So we will talk about the macro-nutrients.

Nitrogen Plants use nitrogen to grow foliage and it is used up very quickly by most plants. Lack of nitrogen causes stunting and yellowing of older foliage. This is by no means the only thing that causes yellowing so be careful. Check your plant for other symptoms before feeding. Make sure yellowing is mainly on older growth and not on young shoots.

Phosphorus This helps promote strong root growth and will give your tree a look of maturity.

Potassium This works with the other nutrients as a catalyst. It also inhibits the nitrogen preventing it from producing too much soft wood. Potassium aids in the manufacture of sugars and starches, it also helps produce chlorophyll. It is good for fruit and flowers and builds resistance to cold.

Calcium Calcium is used to build the cell walls it also makes phosphorus and potassium more available to the plant. Don't over use it on acid loving plants like azaleas, it will make the soil alkaline.

Sulphur Sulphur is part of the molecules that make up plant proteins, a deficiency may lead to weak root development and paler foliage.

Ok so
Fertilizer companies are required by law to tell you how much of three of these macro-nutrients are in their products. They are Nitrogen, Phosphorus, and Potassium. They will be marked as a ratio of N.P.K. Some N.P.K. numbers seem low 2-1-3 others high 24-4-16. This is because they are expressed as a total percentage of the packaged weight. The powder nutrients tend to have higher N.P.K. values than liquid as they are not already partially diluted in water. You could give yourself a headache trying to work it out. Don't worry too much; what you need to look for is a good balanced ratio where all three numbers are very close to each other, unless you particularly want to boost one of the characteristics promoted by a particular compound in that ratio.

Organic versus Chemical


    Less chance of burning
    Slower acting, won’t bolt the tree
    Encourages beneficial bacteria

    A lot of people are using sterile potting mix without the bacteria in the soil organic food will not work very well.


    You can buy varying degrees of nutrients
    You can get slow release (Osmocote etc)
    Ease of use/no smell

    Can burn trees roots
    Can harm useful bacteria

Organic fertilizer
The fish based fertilizer is good watered in thoroughly every 2-3 weeks in spring and autumn. Be sure to water until it reached the bottom of the pot. If you only have a few trees it may be best to mix up a bucket and dunk your trees to make sure. You don't want to water only a section of the soil or it will draw the roots to the surface.

Here is a recipe I got from Deborah Koreshoff's book "Bonsai Its Art, Science, History and Philosophy" that I managed to pick up on trademe. (The book is out of print) It is a great book.

3 parts soya bean meal 1 part blood and bone 1 part chicken manure 1 part wood ash 1 part fish emulsion

Place all the ingredients into a container, 4 times the volume and add water to bring it to half way. Put a lid on and leave it to bubble away for about 3 months. After it is fermented top up the bin withwater. Use one part of this mix to five parts water and dunk or water your plants thoroughly.

You can also make small fertilizer cakes from the same mixture by adding less water allowing it to evaporate. Once evaporated add plain flour to make it sticky and form it into small biscuits. Let these dry in the sun until hard. Just place these on the soil of your trees they will act as a slow release fertilizer.

There are hunderds of different chemical fertilizers that come in powder liquid and slow release pellets. I cannot recommend any one in particular. I will say be careful with what ever one you choose, it is better to mix under the recommended strength and apply more regularly than give your plants one strong dose.

I have been using a mixture of different fertilizers this year to try and find what works best for me. So far I have tried a fish based organic plant food, blood and bone and a pellet form of Nitrophoska Perfect N.P.K.of 15-2-17. The Nitrophoska in particular did wonders for the colour of my elms. As you can see from the N.P.K rating this fertilizer is high in Nitrogen and Potassium and is designed to boost growth. So be careful if you have an older tree it my bolt away with lots of soft growth and cause long gaps between the nodes. Trees that have a juvinile foliage type might also revert back to it if they are feed a high nitrogen food.

Good luck with your plants and remember go easy a weaker solution more frequently is better than one large shock dose.

Here is a link to the page on Pohutukawa if you would like more information on this tree.

If anyone has a subject they would like covered in these newsletters please let me know. I will do my best to answer any questions.
For those of you that are still after tools we have not forgotten. Another e-mail was sent to China yesterday to find out where they are, we will let you know as soon as we do.


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