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Knowing More about Plant Nutrient/PH Requirements

Knowing More about Plant NutrientPH Requirements

All plants in nature or cultivated require Nitrogen, Phosphorous, Potassium, Calcium, Magnesium and Iron plus all the minor elements at varying levels depending on the plant. But, unless the pH of your soil isn’t in the proper range, then tons of fertilizer won’t help.

So when I say the ph of the soil is important — it is! Look at the chart below: ph 6.5 is the point where most elements are available. Soil pH is a relative measure of the level of acidity or alkalinity of the soil, the lower the number, the more acid, the higher, the more alkaline. 7.0 is considered neutral.. See Horticultural Trivia for a literal definition of pH.

pH Bar Graph


This bar graph gives the pH ranges at which plant nutrients will be most available. The wider the bar, the more available the nutrient. Calcium, magnesium and potassium–the exchangeable bases–are most available at high pH and unavailable at low pH.

Nitrogen and sulfur have similar available pH ranges. Iron, manganese, zinc, and copper are less available at high pH values. Phosphorus and boron are unavailable at both low pH and high pH.

Fertilizer Elements

Plants in nature or grown in an organically rich garden environment receive their nutrient naturally from decomposed and recycled plant matter that add the necessary nutrient to sustain the plant in a healthy and well-balanced manner.

However, potted plants don’t enjoy this same benefit and may need some help in achieving the proper pH and nutrient balance required for their healthy growth. Packaged fertilizers and soil supplements may be needed in such cases.

Packaged fertilizers are required by law to have the percentages of nitrogen (N), phosphorus (P), and potassium (K) printed on the bag. You will see 10-10-10 or 25-15-30, etc. The numbers represent the percentage of each nutrient in the product, the first number is for nitrogen, the second for phosphorus and, the third for potassium.

Many chemical fertilizers will also contain trace elements and minor nutrients (minerals such as calcium, iron, magnesium, etc.), all of which are necessary in very small amounts for good plant growth. The label will list the percentages of these microelements as well.

For a bag of fertilizer with an NPK of 10-10-10, the customer knows that 30% of the bag is actual fertilizer, 70% will be fillers or a “carrier.” It makes good economic sense to buy the product with the highest total percentage but remember you must know your plants’ needs first. If the percentage is higher read the instructions carefully since you may need to apply LESS than the manufacturer recommends!

The following discussion centres on the basic nutrient element needs of plants whether received naturally or from artificially produced fertilizers.

NITROGEN provides growing power and makes plant leaves and stems green.
Nitrogen is used to form basic proteins, chlorophyll, and enzymes for the plant cells. In short, a plant can’t grow without it.

Your plants use the nitrate or nitric form of nitrogen immediately because they’re soluble. But over-watering can wash them away. The ammonium types of nitrogen will take from two weeks to three months for the plant to use, but won’t leach out of the pot.

When using fertilizers, check the package to see which kind of nitrogen you’re getting. The “N” number of the “N-P-K” formula will tell you the percentage of nitrogen, by weight, in the mix. A “quick release” fertilizer will contain nitrates so your plant can use them right away. “Slow-release” indicates the ammonium form of nitrogen. Ammonium nitrate is actually a half-and-half mix of nitric oxygen (quick release) and ammonium nitrogen (slow-release).

When fertilizing, remember that too much nitrogen can be as bad as too little. Plants can suffer nitrogen burn or grow so much foliage that they never flower.

PHOSPHORUS stimulates budding and blooming

Plants need phosphorus to produce fruits, flowers, and seeds. It also helps make your plants more resistant to disease. Phosphorus doesn’t dissolve like nitrogen. The soil will hang onto phosphorus, not releasing it into water.

If you’re looking for good sources of phosphorus, check the ingredients of any plant food you buy. The “P” number of the “N-P-K” formula will tell you the percentage of phosphorus, by weight, in the mix. You should also look for ingredients like bonemeal, colloidal phosphate, or rock phosphate.

You may also see super-phosphates, a more soluble form of phosphorus. Be careful with these: Overfeeding with super-phosphates can actually create phosphorus deficiencies because they wash away too easily (the perils of a “quick fix”).

POTASSIUM promotes strong vigorous roots and resistance to disease

Potassium is a nutrient your plants need for good internal chemistry. Plants use potassium to produce the sugars, starches, proteins and enzymes they need to grow and thrive. Potassium also helps your plants regulate their water usage, and better withstand the cold.

Other Microelements

Your plants need certain trace elements and nutrients to make the best use of soil, water, and air. An important thing to remember about trace minerals is that plants can’t always use the most common forms. If your garden store supplies them, get the chelated forms of the trace minerals. Chelated minerals have already gone through the chemical changes that make the minerals usable to your plants.

Magnesium (Mg) and Iron (Fe) are the “chlorophyll helpers.” They’re both important to the plant’s production of chlorophyll. Magnesium, in fact, makes up the core of the chlorophyll molecule. Dolomitic lime and epsom salts are good sources of magnesium. To supply your plants with iron, try spraying liquid seaweed or chelated iron.

Calcium (Ca) and Boron (B) are essential for proper water uptake, and both are important for proper cell formation. Calcium is present in gypsum, lime, and oyster shells. Boron is available in borax and a chelated boron spray.

Sulfur (S), Zinc (Zn), and Manganese (Mn) are the “catalysts” that help other nutrients such as nitrogen become usable by your plants. Gypsum and flowers of sulfur are good sources of sulfur. The others are available in chelated form, usually as a spray.

Don’t worry — remember, all of the above can be found in ready-made mixes such as peters or miracle-gro.

Deficiency signs:

Nitrogen deficiency:

Older leaves turn a pale green and the veins are usually a reddish colour. New growth will be stunted.

Phosphorus deficiency:

The veins will turn red to purple and the plant as a whole will look purplish.

Potassium deficiency:

Causes the edges of older leaves to be a purple colour and the leaf tips will be a brownish color.

Magnesium deficiency:

First appears on older leaves where they turn a spotted yellow or tan color.

Zinc deficiency (rare):

Will look almost like magnesium but here the leaf will be twisted.

Iron deficiency:

Young growth is stunted and pale — you’ll know its iron if the veins on the leaf remain green.

Calcium deficiency:

Dead areas appear in young growth and the tips soon die.