Fertilizer Notes
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Six Primary Nutrients
There are six primary nutrients that plants require in fairly large quantities.
1. Carbon from CO2 in the air
2. Hydrogen from water
3. Oxygen from water and air
4. Nitrogen helps plants make the proteins they need to produce new tissues. In nature,
nitrogen is often in short supply so plants have evolved to take up as much nitrogen as
possible, even if it means not taking up other necessary elements. If too much nitrogen is
available, the plant may grow abundant foliage but not produce fruit or flowers. Growth
may actually be stunted because the plant isn't absorbing enough of the other elements it
needs. Additionally, too much nitrogen can cause plants to be more susceptible to
diseases, fungi, frost and infestations. Yellow leaves are a sign that the plant contains too
little nitrogen. More nitrogen is needed in the growth phase.
5. Phosphorus promotes respiration, energy supply and stimulates root growth, helps the
plant set buds and flowers, improves vitality and increases seed size. It does this by
helping transfer energy from one part of the plant to another. Phosphorus can also extend
the shelf-life of the crop. To absorb phosphorus, most plants require a soil pH of 6.5 to
6.8. Organic matter and the activity of soil organisms also increase the availability of
phosphorus. Too little phosphorus and a plant’s leaves will turn purple or blue with
lateral roots that fail to grow well, causing the plant to remain small. Too much
phosphorus (quite rare) can harm the plant indirectly due to a lack of trace elements.
6. Potassium improves overall vigor of the plant. It helps the plants make and transport
carbohydrates [and water] and provides disease resistance. It also helps regulate
metabolic activities, increases plant firmness, fruit and root development. Too little
potassium affects root development, and the plant looks limp. To much and the salt
concentration will be too high, and the plant will absorb fewer nutrients. More potassium
is needed in the flowering phase.
 Potash: Fertilizer potassium is sometimes called “potash”, a term that comes
from an early production technique where potassium was leached from wood
ashes and concentrated by evaporating the leachate in large iron pots (“pot-ash”).
Clearly, this practice is no longer practical and is not environmentally sustainable.
In food production, potassium is removed from the soil in harvested crops and
must be replaced in order to maintain future crop growth. There are several kinds
of potassium that can be utilized for fertilization. It just depends which and how
much accompanying element is desired.
1. Potassium Chloride: The importance of chloride is frequently
overlooked, but it is an essential nutrient for plant growth. Recent research
has demonstrated that many crops respond favorably to chloride
applications with greater yield and quality. Like any soluble fertilizer, saltinduced damage can result if large amounts are placed in close proximity
to seeds or seedlings. Potassium chloride is usually the least expensive
source of potash.
2. Potassium Sulfate: All crops require an adequate supply of sulfur to
develop proteins and enzymes. Sulfur-deficient plants appear light green
and have reduced yields and quality. Sulfate that is present in potash
fertilizers is immediately available for plant uptake.
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3. Potassium-Magnesium Sulfate: Because its vital role in chlorophyll,
magnesium deficiency is first exhibited by yellow leaves in the lower part
of the plant. Magnesium requirements vary considerably, with legumes
generally containing more of this element than grasses.
4. Potassium Nitrate: An abundant supply of nitrogen is essential for all
high-yielding crops. For crops that prefer a nitrate source to an ammonium
source of nitrogen, this potash source can be a good option.
Three Additional Nutrients That Matter
Plants also need these three nutrients, but in much smaller amounts:
1. Calcium is used by plants in cell membranes, at their growing points and to neutralize
toxic materials. In addition, calcium improves soil structure and helps bind organic and
inorganic particles together.
2. Magnesium is the only metallic component of chlorophyll. Without it, plants can't
process sunlight.
3. Sulfur is a component of many proteins.
Micronutrients
Finally, there are seven elements that plants need in tiny amounts. Healthy soil that is high in
organic matter usually contains adequate amounts of each of these micronutrients:
 boron
 copper
 iron
 molybdenum
 zinc
 chlorine
 manganese
In general, the nutrients in organic fertilizers are not water-soluble and are released to the plants
slowly over a period of months or even years. For this reason, organic fertilizers are best applied
in the fall so the nutrients will be available in the spring. These organic fertilizers stimulate
beneficial soil microorganisms and improve the structure of the soil. Soil microbes play an
important role in converting organic fertilizers into soluble nutrients that can be absorbed by
your plants. In most cases, organic fertilizers and compost will provide all the secondary and
micronutrients your plants need.
Synthetic fertilizers are water-soluble and can be taken up by the plant almost immediately. In
fact applying too much synthetic fertilizer can "burn" foliage and damage your plants. Synthetic
fertilizers give plants a quick boost but do little to improve soil texture, stimulate soil life, or
improve your soil's long-term fertility. Because synthetic fertilizers are highly water-soluble,
they can also leach out into streams and ponds. Synthetic fertilizers do have some advantages in
early spring. Because they are water-soluble, they are available to plants even when the soil is
still cold and soil microbes are inactive. For this reason, some organically-based fertilizers also
contain small amounts of synthetic fertilizers to ensure the availability of nutrients. For the longterm health of your garden, feeding your plants by building the soil with organic fertilizers and
Fertilizer Notes
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compost is best. This will give you soil that is rich in organic matter and teeming with microbial
life.
Foliar Feeding?
[in reference to inorganic] Plants can absorb nutrients eight to 20 times more efficiently through
their leaf surfaces than through their roots. As a result, spraying foliage with liquid nutrients can
produce remarkable yields. For best results, spray plants during their critical growth stages such
as transplanting time, blooming time and just after fruit sets.
Applying organic NPK fertilizer to the soil occurs in several ways. Composts can be dug into the
soil before planting, while ingredients such as bone meal and rock phosphate can either be mixed
into the soil or sprinkled on the soil’s surface. Fertilizer that is applied directly to the surface of
the soil will be gradually worked into the ground by the rain and watering.
What About pH?
Even if proper nutrients are present in the soil, some nutrients cannot be absorbed by plants if the
soil pH is too high or too low. For most plants, soil pH should be between 6.0 and 7.0. Lime or
wood ash can be used to raise pH; sulfur or aluminum sulfate can lower pH. Keep in mind that
it's best to raise or lower soil pH slowly over the course of a year or two. Dramatic adjustments
can result in the opposite extreme, which may be worse than what you started with. Once again,
a helpful solution is to apply compost. Compost moderates soil pH and is one of the best ways to
maintain the 6.5 ideal.
How to Choose a Fertilizer
In most cases, an all-purpose, 5-5-5 fertilizer will provide the nutrients all plants need for healthy
growth. If a soil test reveals certain nutrient deficiencies, or if you want to tailor your fertilizer to
the needs of particular plants (tomatoes vs. flowers), you can select a special formulation. What
you choose will depend on your soil and what you are growing.
The three numbers that you see on a fertilizer label, such as 5-5-5, tell you what proportion of
each macronutrient the fertilizer contains. The first number is always nitrogen (N), the second is
phosphorus (P) and the third is potassium (K). This "N-P-K" ratio reflects the available nutrients
by weight contained in that fertilizer. For example, if a 100-pound bag of fertilizer has an N-P-K
ratio of 5-7-4, it contains 5 pounds of nitrate (5%), 7 pounds (7%) of phosphate (which contains
phosphorus), 4 pounds (4%) of potash (which contains potassium) and 84 pounds of filler.
Note that the N-P-K ratio of organic fertilizers is typically lower than that of a synthetic
fertilizer. This is because by law, the ratio can only express nutrients that are immediately
available. Most organic fertilizers contain slow-release nutrients that will become available over
time. They also contain many trace elements that might not be supplied by synthetic fertilizers.