Fertilizing a garden

April 12, 2011

Proper fertilization of a garden takes some effort.  If you are like most people you buy a bag of mixed fertilizer like a 12-12-12, or 19-19-19 and spread it over the garden.  During the summer many then water the garden with a soluble fertilizer like Green Light’s Super Bloom or Miracle Gro.  Most of the nutrients are probably wasted.  Please fertilize correctly, the wasted nutrients end up in our wastewater, streams and eventually in the ocean.  This causes local, state, and federal governments to enact rules that make it very difficult for fertilizer companies to get products to the market.  The EPA ends up getting involved with increased regulations.

The nutrients plants need are:

Nitrogen – produced quick growth and has numerous functions.

Phosphorus – is a component of proteins, phospholipids and nucleic acids.

Potassium – supports fruit development and regulates opening and closing of stomata.

Calcium – strengthens stalks and stems and influences cell membranes.

Magnesium – is essential in the chlorophyll molecule and for photosynthesis.

Sulfur – is essential in several amino acids that make proteins and enzymes.

Iron – is required for chlorophyll formation and other biochemical processes.

Manganese – influences photosynthesis and chloroplast structure and oxygen evolution.

Copper – is essential to photosynthesis and for respiration as part of cytochrome oxidase.

Zinc – is essential in NADH dehydrogenase and other photosynthesis enzymes.

Molybdenum – is required for nitrogen use, it helps transform nitrates to amino nitrogen.

Boron – regulates carbohydrate metabolism & helps cells determines cell differentiation.

Chlorides or chlorine – is required for photosynthesis.

Cobalt – A new addition to the required elements, helps legumes fix nitrogen.

Sodium – is involved in osmotic regulation and can or may do what potassium does.

Some plants use silica and selenium.  Silica may strengthen cell walls, stems and stalks.

An average crop needs about 150 units of nitrogen per year, plus a similar amount of phosphorus and potassium.  Most crops need about 20 lbs of calcium, magnesium and sulfur.  Only a few ppm are needed of the other nutrients usually called micronutrients.  Most soils can supply everything except nitrogen, phosphorus and potassium. 

Lack of nutrients generally causes stunted plants.  Shortages of certain nutrients cause color streaking in the leaves and improper flower and fruit formation.  As important as having a shortage of nutrients is not to have excessive amounts.  Excessive nutrients are wasted and can cause damage to the plant.  Too much taken up by the plant often causes leaf burn in the plant.  Soils with excessive nutrients often have a white crust develop on the surface after heavy rains dry up.  The nutrients come to the soil surface as water evaporates leaving the salt on the soil surface. 

A good rule of thumb on a garden is to add about 10 lbs of fertilizer for 1000 sq ft of garden.  Then a similar amount can be added either with irrigation or again sprinkled on the surface a couple of months later when plants really start to produce fruits and flowers.  Additional nutrients will only be wasted.  Fertilizers should contain a good amount of nitrogen to support good vegetative growth early in the season.  Later when plants are starting to bloom or produce fruit a higher amount of phosphorus and potassium may be needed.  Grass type crops such as lawns and sweet corn need more nitrogen throughout the whole growing season. 

Certain soils will be short of some micronutrients.  Iron and zinc are the most common micro nutrients that are short.  When these are needed, it is usually because the soil has too high of a pH.  This may be alleviated with additions of iron in products like Green Light’s Iron and Soil acidifier or Ironite.

As important or more important as adding fertilizer is to have the correct soil pH.  PH is a measure of the acidity of the soil.  A good soil pH is 6.5.   Low pH soils can be raised with the addition of calcium, usually in the form of lime.  Powdered lime will influence the soil faster than aggregates of lime.  Pelleted lime is easy to apply but needs to be in a form that the pellets will dissolve in water leaving a powdered lime.  Gypsum can be added to get sulfur and calcium but it neither raises nor lowers the soil pH.  Sulfur will lower soil pH but lowering pH usually takes longer and is less critical than raising the pH.