One of the things that never cease to
amaze me is how many commercial nursery
growers in India never fertilize their
pot plants. Most of those that do either
use an agricultural grade mixed fertilizer
(such as Sufala, 15:15:15) or veer straight
to the other end and use imported fertilizers
costing Rs.50- Rs.100 per kg.
Why is it essential to fertilize pot
plants? There are several conditions unique
to growing plants in pots:
1. The root zone in pots is almost always
limited and the amount of media that the
plant roots can exploit is always smaller
than it would be in the ground.
2. Pots are watered very frequently,
often every day. This leaches away the
soluble elements like Nitrogen and Potassium.
Worse, the warm times of the year when
the plant can utilize the maximum of nutrients
are also when maximum watering is done
with consequent leaching of the very nutrients
the plant needs.
3. Ideally pots are filled with a low
nutrient soiless media- this low nutrient
level has its advantages in the initial
growth stages but it also means nutrients
must be added soon. Also, the components
used usually do not hold and store as
much nutrients as soil so there is the
need to fertilize on a regular basis rather
than give large amounts occasionally.
4. Growing plants in pots is a high value
and high capital cost business where it
pays to produce a good, saleable plant
as quickly as possible. Fertilizer costs
are negligible as compared to the quality
improvement and cutting down of growing
Fertilizing plants is a relatively complex
process but it isn't rocket science. Provided
one understands the fundamental facts
and issues in the process it is possible
to substantially meet the nutritional
needs of your plants and get decent if
not the best possible results at very
reasonable cost indeed.
The basic concepts that need to be understood
1. Organic & Inorganic fertilizers
2. Macronutrients and Micronutrients
3. Practical Issues- concentration &
EC, mixing, problems, delivery and costs
ORGANIC & INORGANIC FERTILIZERS:
This is a complex issue for all but the
most obvious fertilizers- those of animal
or plant origin are organic, those of
artificial or chemical origin are inorganic.
Fortunately ornamental plant growers need
not get deep into these issues, unlike
growers of food crops.
For practical purposes:
Organic fertilizers are items like animal
manures, blood & bone meals, leaf
mould etc. Specialized growers, especially
in the Far East make various organic teas
from molasses, plant wastes etc.
The main points to remember are:
· They are usually dilute fertilizers
with low concentrations of plants nutrients
· Nutrients are complex, undefined
· The Nitrogen is in the form
if Ammonia ions which has several implications
· Many nutrients are released
slowly though this is not always the case.
This slow release ability is one of the
most important attributes for using organics
in ornamental pot plant production.
· May seem cheap by the ton but
are costly in terms of nutrients contained
· Supply humus, micronutrients
and complex nutrients.
Inorganic fertilizers are either single
chemicals- Potassium nitrate, Calcium
nitrate, Monopotassium Phosphate, Urea
etc or complex fertilizers like Sufala
(15:15:15). The main points to remember
· These are chemicals that can
be defined: thus Potassium nitrate, subject
to purity levels, is the same anywhere
in the world and it makes absolutely no
sense to pay 2-3 times more for imported
material when local material of equal
analysis is available. Despite all the
hype, color brochures and fancy packing,
it will give the same results as the local
· The analysis for many chemicals
is simple and obvious, the complex fertilizers
being the exception. These complex fertilizers
are manufactured for agricultural use
and have the only advantage of being cheap
due to government subsidy and must be
used after trials and with caution.
· The nutrient concentration is
high- this means they must be used with
care and adequate dilution. They may be
costly by weight but are cheap in terms
of nutrient content.
· The nitrogen can be in Ammonia
form but can be selected to be in purely
Nitrate form too.
· Nutrient availability is usually
immediate but may be modified for slower
release. We do not discuss coated slow
release fertilizers like Osmocote here
as they are too expensive in India.
In the vast majority of situations inorganic
fertilizers will best serve the needs
of the pot plant grower. The two situations
where organic fertilizers are used are
in the form of animal manures in the potting
media and as pelleted chicken manure as
a slow release fertilizer-these not only
provide nutrition during growth in the
nursery but are critical in providing
post production nutritional support to
the pot plant at the buyer's location.
MACRONUTRIENTS AND MICRONUTRIENTS:
For practical purposes, the fertilizing
program needs to provide a limited number
of elements to the plant. These are listed
below along with examples of common chemicals
that will provide that element.
The elements needed are divided into
macronutrients and micronutrients. The
former are required in large quantities
compared to the latter. For example, we
use 1-2 grams per one liter water of Calcium
nitrate+ Potassium nitrate in the liquid
feed to provide the macronutrients Calcium,
Potassium and Nitrogen; compare this to
1-2 grams per 100 liters water of Copper
Sulphate to provide the micronutrient
Nitrogen (N): required in large amounts
for plant growth. Plants lacking N show
poor growth and are weak and stunted.
Acute shortage leads to yellowing and
fall of lower leaves. The most limiting
element when plants are grown without
inorganic feed but usually more than adequate
in a well fertilized nursery.
There are two forms: Nitrate and Ammonia.
Both provide N but nitrate is generally
preferred and should form at least 50%
of the N. Ammonia leads to excessive tall
growth, soft tissue and can be toxic to
many ornamental species. Reaction varies
from species to species though- Scindapsus
prefers Ammonia N.
Ammonia N also has a strongly acidifying
action on the media pH and this is an
issue especially with long term crops.
Commonly used chemicals include Potassium
nitrate, Calcium nitrate, Ammonium nitrate
and Urea. The last two are pure Nitrogen-
Ammonium nitrate providing 50:50 Ammonia
and Nitrate N while Urea is 100% Ammonia
N. All are totally soluble in water.
Phosphorous (P): One of the elements
most misrepresented by fertilizer manufacturers
over the years. It is an essential element
and deficiency will give stunted plants
with small, deep green leaves and poor
flowering. However, relatively little
P is required by most plants and there
is no need for the high levels of P often
seen in "Flower Booster" and
similar fertilizers. Such high levels
lead to excessively long and stretched
growth of many plants. Even higher levels
will lead to micronutrient deficiencies
as the P reacts with them and makes them
Another point to remember is that clay
in soil will bind a lot of phosphorous:
some soils are so poor in P that initial
applications will all be totally absorbed
to fill this "hunger". In soiless
media P is not bound and is easily available
as well as easily leached and will require
Current thinking on P is to use it at
very low basal levels (5-10% of the N
level) and use it to control plant height
and growth. If the plants are too stunted,
increase P; if too tall, reduce P levels.
Commonly used chemicals include single
Superphosphate (which is 50% Calcium sulphate
and so it provides Calcium & Sulphur
too), Monoammonium phosphate and Monopotassium
phosphate. The last two are totally soluble
forms. Monopotassium phosphate is also
used for foliar sprays where it also has
Potassium (K): Also required in large
quantities, it is important for structural
strength and disease resistance in the
plant and for flowering and fruiting.
Deficiencies are seen as lower leaf edge
burn followed by leaf drop and naked lower
stems. As with N, deficiency of K will
be unlikely in well fertilized nurseries.
It is easily leached from the media (as
well as leaves by heavy rain).
Commonly used chemicals are Potassium
nitrate and Potassium sulphate. A cheap
alternative is Potassium chloride (Muriate
of Potash or MOP). Never use this for
pot plants as chloride toxicity can ruin
Magnesium (Mg): this element is critical
for chlorophyll molecule and deficiency
is seen as interveinal chlorosis of lower
leaves, often with bright red coloration
followed by burnt interveinal areas and
leaf drop. We have little experience with
Mg deficiency since our soil and water
are naturally high in Mg. A common chemical
source is Magnesium sulphate (Epsom salts).
Calcium (Ca): Like the above elements,
Calcium too is required in large amounts
but is generally neglected and is commonly
deficient. The symptoms of this are quite
characteristic- starting with poor development
and paleness of leaf tips and followed
by dying (necrosis) of the tips. More
severe deficiency will lead to extreme
reduction in size of new leaves followed
by tip death. Flower buds abort and any
fruits show typical "blossom end
necrosis" - the drying and death
of areas furthest from the stalk and nearest
the stigma. Calcium deficiency is a complex
problem and can occur due to a number
of reasons other than actual lack of Calcium
in the media. It is more common than is
generally recognized. Common chemical
sources are Calcium nitrate, Calcium chloride
and Calcium sulphate (Gypsum). Calcium
nitrate is the best source, clean and
fully soluble. Gypsum can be used as a
media additive but avoid marine gypsum
which has Sodium chloride. Often the only
way to clear a Calcium problem is to spray-
use Calcium nitrate or Calcium chloride
at 5 grams per liter of water for this
K:Ca:Mg ratio is an important concept:
this should be in the region of 5:3:1
and any significant deviation from this
will lead to problems. For example, in
our growing system, we use coir which
is naturally high in K and low in Ca.
Also our water is high in Mg. This leads
to an imbalance in this ratio and Ca deficiency
is a common problem. We use Calcium nitrate
in the liquid feed and as foliar sprays
to control this problem.
Sulphur(S): Another nutrient required
in relatively large quantities but rarely
short when plants are well fertilized.
It is present in water from around industrial
areas and cities and present in single
superphosphate, gypsum etc. Deficiency
is seen as a general, overall chlorosis.
Iron (Fe): The micronutrient required
in largest quantities. Deficiency is seen
as a characteristic chlorosis of new leaves,
which slowly go completely white. Very
often the problem is more than a simple
lack of Fe in the media. It can be root
damage due to any reason, often water
logging of the roots. It can also be due
to high media pH at which the Fe becomes
Common source is Ferrous sulphate- this
is often useful but won't work if media
pH is the problem. In this case the short
term solution is to use chelated Iron,
especially Fe-EDDHA if available. The
long term solution is to lower media pH-
use acidifying fertilizers, use nitric
or phosphoric acids to lower irrigation
water pH etc.
Manganese (Mn): deficiency symptoms are
very similar to Fe: chlorosis of new growth.
This is often accompanied by necrotic
spots on the leaves. As I read somewhere-
"only the very experienced or the
very foolish will try to distinguish between
Manganese and Iron deficiencies on symptoms
alone". Manganese sulphate can be
used as drench or a chelated form is used
as a spray.
Copper (Cu): Quite a common problem when
using high organic media containing coir,
peanut shells etc because these materials
bind copper. Deficiency affects new growth-
leaves are small, narrow and with some
paleness. Often new growth seems "sticky"
and leaves get caught in each other. Flowers
become small and quite characteristically,
flower color fades markedly. Chelated
Copper sprays can be used but a drench
with Copper sulphate at 10-25 grams per
1000 liters of water works very well.
We use this every 6 months and whenever
a problem is seen (this is often in spring
when temperatures are beginning to rise
and plant growth increases). Excess Cu
due to too much of the above drench will
show Cu toxicity in the form of iron deficiency
Zinc (Zn): Another micronutrient which
often gives problems- new growth is affected
with leaves becoming smaller, closely
spaced (rosseting) and often one side
of the leaf will be malformed, leading
to a leaf twisted in one direction. Bright
variegation like chlorosis may be occur.
Flower and fruit drop is seen.
We drench with Zinc sulphate along with
the Copper sulphate at the same rate as
above to prevent any problems.
Boron (B): A non metallic element, often
deficient in open well drained media and
after heavy rains as it leaches easily.
New growth is severely affected with basal
areas of newly formed leaves showing abnormalities.
The midrib is distorted and often the
leaves look like the mid rib is too short
for the leaf and the leaf blade is corrugated
In severe cases buds drop and fruits
abort and new growth ceases. Stems &
fruits develop corky areas and may crack
and exude gum.
It is difficult to differentiate between
Calcium and Boron deficiency symptoms,
especially when mild. Typically, however,
boron affects the basal areas of the leaf
and Calcium the distal or tip region.
Common chemicals used to supply B are
boric acid (needs hot water to dissolve)
and Solubor, an easily soluble, more concentrated
form. Take care with B- toxicity is also
common and many plants are particularly
sensitive, e.g. Euphorbia milii
Molybdenum (Mb): rarely seen deficiency
except in some vegetables (Cruciferae)
and is a problem with Poinsettia. Sodium
molybdate is used at extremely low concentrations
as a preventive measure.
The above chemicals can be used to make
a complete nutrient solution supplying
all the plants needs. How much of each
to use is also relatively easy to decide
if you know the percentage of each element
in the chemical you use. Details of this
are beyond the scope of this article and
can be found in any good text book.
Some practical guidelines are:
· Keep it simple: use the minimum
number of chemicals to provide all the
nutrients. Complex formulations will not
give better results.
· Have a plan: for example, add
Super phosphate to the growing media to
provide P, Ca and S. Use a simple mix
of Potassium and Calcium nitrate to provide
K, Ca and N. Add Magnesium sulphate if
Mg is needed. Micronutrients can be added
as a drench as well as occasional foliar
· Add nutrients as needed- e.g.
N in the form of Ammonium nitrate to boost
growth and green up foliage plants or
P in the form of Monopotassium phosphate
to get taller plants.
· Remember some chemicals will
react in solution, e.g. Calcium and phosphorous
will react to give an insoluble powder
that will settle out of the solution.
Do not mix such solutions together, apply
· Mix solutions thoroughly: we
dissolve the powder in large tanks by
adding the chemical to a little water
and then starting the pump to fill the
tank- the large amount of water falling
in mixes everything.
· Check the EC of the fertilizer
solution: this is more important than
blindly following a formula. The acceptable
EC depends on the plant, the season etc
but experience will tell you the level
that is acceptable. About 3.0 micro siemens
should be generally the maximum. In fact
it is possible to feed by EC only- decide
on what you need to use and add enough
to reach your target EC. We generally
use two parts of Calcium nitrate and one
of Potassium nitrate and add enough water
to get to an EC of 2 -3 depending on the
crop and the season.
· Getting the fertilizer solution
to the plants is not easy. The best way
is to use a measured mug or bottle and
drench each pot individually- this becomes
impossible with large number of pots.
We use our watering wands to apply the
fertilizer solution. This works best with
square pots in our MP trays as there is
little wastage. With round pots there
is some waste. For larger pots and tubs
we use the Junior watering wands to apply
the fertilizer solution to each pot individually.
· Drip irrigation can be used
to deliver the liquid fertilizer. In this
case use good grades of fully soluble
chemicals and quality filtration.
· Costs are much lower by using
the specific chemicals. Most chemicals
cost less than Rs.20/- per kg. Commercial
fertilizers like Urea, Diammonium phosphate
and Ammonium nitrate are much cheaper.
Using imported fertilizers will not give
better results except for some specialty
chelates like EDDHA. Whenever trying out
costly fertilizers, try local materials
as controls. Very often plants are so
starved that almost anything will give