Bonsai need feeding. The concept
that trees need to be starved to keep them small is one that is
totally wrong and will lead to failure every time. A plant, any
plant, whatever size and wherever it is growing needs nutrients
just as humans need food.
For those of you who have read our article on Bonsai potting mediums
you will realise that the use of inorganic potting mediums such
as Akadama, Kyodama and baked clay granules makes for a perfect
physical environment in which to grow a tree but there are no nutrients
present in any of the raw ingredients. This has the disadvantage
that nutrients must be added for it to work. I prefer to focus on
the advantage thats you can add exactly what you want and can monitor
the effect of your feeding regime for future reference to produce
the desired result. For those of you using organic ingredients,
the supplies of nutrients are there to start with but you have no
way of knowing how much there is and can not predict at what rate
it will be released into your rootball.
Lets get the technical stuff out of the way now before anyone
nods off, just so we have some reference if we need it later.
The main components of any fertiliser are Nitrogen, Phosphorous
and Potassium, universally identified by the N-P-K ratio shown on
the packaging. Loosely speaking, Nitrogen(N) is used by plants for
leaf growth, Phosphorous(P) for root-growth and Potassium(K) for
flower and fruit production. There are then a number of trace elements
that are essential in small quantities and are not really worth
worrying about because they are included in just about all proprietary
The N-P-K ratio will guide you in the proportions of each of the
main nutrients. A perfectly balanced fertiliser will logically have
the numbers all the same eg 5-5-5 or 20-20-20. The numbers are an
indication of the strength of the feed so 5-5-5 would be considered
fairly mild (Chicken Korma) while 20-20-20 is pretty strong (Beef
Madras). I prefer to use regular doses of milder feed rather than
a blast of strong stuff as the tree will better be able to use it.
It is also possible to control the dosage of mild feeds based on
weather conditions whereas a strong feed once in the pot will be
hanging around forming toxins if not used up. These balanced fertilsers
should be considered as a good basis for any feeding regime and
will guarantee good health.
When choosing fertiliser you have a choice between soluble fertilisers
that are mixed with water and slow release fertiliser that comes
in granules or pellets and break down slowly over time. The liquid
feed is ideal if you are totally dedicated to your trees and can
be there at the right times to feed them. However since most of
us have other distractions in life, pellets can be useful in providing
a slow trickle of feed which will maintain good health in your absence.
I recommend a combination of slow release fertiliser such as Naruko
5-5-5 or Bio-Gold 5.5-6.5-3.5 supplemented with additional liquid
feed tailored to species and developmental requirements. Remember
to take into account the combined amounts given when calculating
any additional feeds.
One popular approach is feed cakes as traditionally used in Japan.
They are usually made of fish-meal or rape-seed and are slow release.
They are placed on the soil surface but being organic they can become
a breeding ground for maggots and can attract fungus which is unsightly.
The smell can also be pretty bad. They work well but the modern
alternatives already mentioned ie Bio
Gold and Naruko are designed to give a slow release without
the visitors, hairy growth and odour.
We've touched already on what each component does but let us now
expand on the use of each.
Nitrogen (N) is the high sugar, high carbohydrate component of the
diet. It encourages strong leaf and shoot growth. It is useful in
certain evergeen species as a kick start in the spring where we
want a certain amount of lush growth to form fresh pads but in deciduous
species it should be left out until after the first set of leaves
have hardened and only then used lightly as it will lead to overlong
Phosphorus(P) encourages the growth of roots and flowers. It should
always be given as part of a balanced regime because a plant will
only take up as much phosphorus as it needs.
Potassium (K) Helps the wood to harden, as well as increasing the
roots ability to absorb both nutrients and the water they're dissolved
in. It is an important part of the autumn diet as it prepares the
tree for winter.
So the basic growing season will consist of a balanced diet on
a weekly basis during the spring with no excesses of anything on
the whole to encourage good but controlled growth. During the height
of summer growth will grind to a halt. Feeding should be reduced
or suspended at this time. A second burst of growth in early august
can be accompanied by a balanced feed before switching to low nitrogen
feed for the run up to winter which will harden existing growth,
form healthy new buds and slow any fresh growth which will not have
time to harden anyway and will only die back..
There are of course exceptions to this general approach. There
are too many to cover in detail but here are a few examples where
thought is required.
Indoor trees will be active most of the year but will slow down
during winter. They should be fed all year round but less should
be given during winter. It is tempting to encourage lush growth
in the winter months but without the light levels to support the
new growth it will tend to be leggy and will ultimately need to
be removed. For small user bottles of liquid
feed are readily available to dilute as required.
Lime-hating plants such as Azaleas require regular supplements
to maintain their acidic soil ph and chelated iron levels.
Many Pine species and Juniper species also benefit from twice yearly
'acid' feeds. Suitable fertilisers include Miracid or any other
fertiliser that is indicated as being specifically for ericaceous
or lime-hating plants.
As mentioned deciduous trees in general, especially those at the
fine ramification stage of development will benefit from a reduced
amount of Nitrogen during spring and summer.
Pine development is a subject all its own with back budding being
a constant battle. I have had good results with an unconventional
approach involving no nitrogen in spring and a good dose in autumn.
Don't ask me to explain the theory behind this approach but it seems
to work and increased back budding in the spring is the result.
A word of caution!
. Now you are armed with all these ideas on how best to feed your
trees it is easy to get carried away. But err on the side of caution
and give too little rather than too much. Too much Nitrogen will
burn roots so always follow the instructions carefully and use the
correct or less than the correct dosage. If you miss a feed do not
be tempted to strengthen the dose or feed at more frequent intervals
to make up and if you suspect that you may have overfed a tree,
water it liberally several times until waer runs freely through
th root ball to flush out the excess. Trees should not be fed when
sick or dormant as they will be unable to use the nutrients provided
leading to excessive levels of toxins in the soil.
For many years the traditional approach to feeding after repotting
has been to wait six weeks. However, trees need some nutrients to
rebuild their trimmed root system so a light feed of nitrogen free
fertiliser would be of benefit especially if using a non organic
potting medium. uld not be fed for at least six weeks to avoid burning
We have only begun to touch on the subject of feeding in this article.
Specialised approaches abound but hopefully you will have gleaned
the knowledge of a good basis from which to explore. As with finding
the right potting medium,
Only cautious and educated experimentation in your own growing environment
will show what is right for you.