Plants Get Hungry Too

Reader Contribution by Karen Newcomb
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Although nutrition is as important to plants as it is to people, many gardeners simply ignore the issue.  Then they wonder what’s wrong with their vegetables.

Vegetables generally need 15 nutrients for maximum growth.  Three elements–oxygen, carbon, and hydrogen–come from air and water.  The other 12 exist in the soil.  Nitrogen, phosphorus, and potassium are the major macronutrients needed by vegetables in large amounts.

Nitrogen, a major element in plant nutrition, produces leaf growth and gives leaves a vibrant dark green color.  It helps generate a healthy root system, increases the set of fruit, and nourishes soil microorganisms.  It is especially important for such leafy vegetables as cabbage, lettuce, spinach, and collardsNitrogen deficiency causes yellow leaves and stunted growth.  Excess nitrogen delays flowering, produces excessive growth, reduces the quality of fruits, and renders crops less resistant to disease.

Blood meal contains 7 to 15 percent nitrogen.  It can be mixed as a liquid fertilizer, using one tablespoon to a gallon of water.  Hoof and horn meal contains 7 to 15 percent nitrogen.  Cottonseed meal has 6 to 9 percent.  Fish meal and fish emulsion contain up to 10 percent nitrogen and nearly as much phosphorus.  Bonemeal may contain up to 3 percent nitrogen.  Follow directions on package.

Phosphorus stimulates early root formation, hastens maturity, and is important for the development of fruit, flowers, and seeds; it also helps provide disease resistance and winterkill protection.  A phosphorus deficiency causes dark or bluish green leaves followed by bronzing, reddening, or purpling, especially along veins and margins.  Lower leaves are sometimes yellow, drying to greenish brown or black.  Plants are often stunted, spindly, late to mature.  Excess phosphorus produces iron and zinc deficiencies in corn, beans, tomatoes, and other plants.

Phosphorus fertilizers include bonemeal, averaging 20 to 25 percent phosphoric acid, and phosphate rock, a finely ground rock powder that contains about 30 to 33 percent phosphoric acid, plus minor and trace elements.

Potash (potassium) is important in plants’ ability to manufacture sugar and starches.  It improves the color of flowers and the length of time fruit is edible.  Potash promotes vigorous root systems and is essential in growing good root crops.  It produces strong stems, reduces water loss, increases vigor, combats disease, and reduces winterkill.  Potash deficiency causes dry of scorched leaves, and there may be small dead areas along the margins and between the leaf veins.  Plants are sometimes stunted and appear rusty while their fruit is often small and thin-skinned.  Excess potash produces coarse, poorly colored fruit.  Nitrogen, phosphorus, and potash (potassium) are provided in standard commercial fertilizers.

Potassium is supplied by granite dust (up to 8 percent potash), hardwood ashes (up to 10 percent), softwood ashes (about 5 percent), and greensand (up to 9 percent).

You should add humus and these three nutrients to your garden before you replant.  You can add dry fertilizers to the soil in the form of a package, preblended organic mix or you can mix your own from organic ingredients.  Every two to four weeks, give your entire garden a supplemental feeding of fish emulsion.  Crops that are heavy feeders will especially benefit from those supplements.

Natural Plant Foods

Composition (%)

TYPE                                      SOURCE         NITROGEN     PHOSPHORUS            POTASSIUM

Animal Manure (fresh)         cattle               0.53                 0.29                             0.48

                                                chicken            0.89                 0.48                             0.83

                                                horse               0.55                 0.27                             0.57

                                                sheep              0.89                 0.48                             0.83

Animal Manure (dried)         cattle               2.00                 1.80                             3.00

                                                horse               0.80                 0.20                             0.60

                                                sheep              1.40                 1.00                             3.00

Animal Tankage                    dried blood      9-14                 –                                   –


                                                bonemeal        1.6-25              23-25                           –

                                                dried fish         6.5-10              4-8                               –


                                                fish emulsion   5-10                 2.0                               2.0

Pulverized Rock Powder     rock                 –                       38-41                           –


                                                greensand       –                       1.35                             4.1-9.5

Vegetable                              cottonseed      6.7-7.4             2-3                               1.5-2.0


                                                seaweed          1.7                   0.8                               5.0

                                                soybean          6.0                   1.0                               2.0


                                                oak leaves       0.8                   0.4                               0.2

                                                wood ashes     –                       1.5                               7.0

Organic Fertilizers

You can buy good organic fertilizer from a nursery or order from the seed catalogs.  You can also mix a worthy organic fertilizer yourself.  Here are three formulas.

FORMULA ONE                                 FORMULA TWO                                 FORMAULA THREE

2 pints blood meal                               4 pints cottonseed meal                      2 pints blood meal

4 pints bonemeal                                 4 pints bonemeal                                 4 pints bonemeal

3 pints greensand                               3 pints greensand                               2 pints woodashes

You can substitute for any nutrient in a formula as long as you keep the same nitrogen: phosphorus: potassium ratio.  For instance, cottonseed meal contains 7 percent nitrogen as compared to the 15 percent found in blood meal; this means you will need roughly twice as much cottonseed meal as blood meal.  Store your mixture in small plastic bags to use when you make up your garden beds.  Pints are easy units to hand, but you can make up these mixes in any quantity as long as you create the same relationship among the ingredients.  For the average garden, use 1 ½ gallons per 100 square feet.


Magnesium, manganese, copper, zinc, iron, sulfur, calcium, molybdenum, and boron are secondary nutrients, or micronutrients, and are needed only in extremely small quantities.  However, it’s important to understand what each of these elements does for vegetables and how to tell if any are missing.

Magnesium is important in chlorophyll production.  It promotes early and uniform maturity and is important in fruit growth.  Magnesium deficiency causes yellowing of the lower leaves at the margins, tips, and between the veins.  The leaves wilt from the bottom up until only the top leaves appear normal.  Magnesium deficiency in corn shows up on the leaves as yellow stripes.  Excess magnesium may produce a calcium deficiency.  Magnesium deficiency can be corrected with a fertilizer containing magnesium sulfate or Epsom salts–about 1 pound per 1,000 square feet of garden space.

Manganese is important for green plant development.  It is essential to both respiration and normal chlorophyll formation.  Manganese deficiency causes stunted growth and mottled yellowing of the lower leaves.  Excess manganese may produce small dead areas in the leaves with yellow borders around them.  A deficiency can be corrected with manganese sulfate.  Follow the instructions on the package.  Organic matter also contains manganese.

An enzyme activator, copper plays vital roles in both chlorophyll and protein formation.  Copper deficiency produces dark green, grayish-olive, or blue leaf edges that curl upward.  Flowering and fruit development is checked, while carrots are poorly colored and bitter.  Excess copper stunts roots and prevents the uptake of iron.  Copper deficiency can be corrected by applying about 6 ounces of copper sulfate per 1,000 square feet.  You can also apply seaweed to the leaves or add well-rotten manure.

Another enzyme activator, zinc is necessary for normal chlorophyll production and cell division.  Zinc deficiency brings about mottling, yellowing, or scorching of the tissues between veins.  Satisfy this need by applying 8 ounces of zinc sulfate per 1,000 square feet.  Ground phosphate rock also contains trace elements of zinc.

Iron promotes chlorophyll production.  Insufficient iron causes mottling, yellowing, or scorching of the tissues between veins.  A deficiency can be correct by using a soluble organic iron complex, iron sulfate, or chelated iron.  Seedweed also adds iron.

Sulfur helps maintain the dark green color of plants.  It is also a constituent of proteins and growth-regulating hormones.  If soil doesn’t have enough sulfur, young leaves turn pale green or yellow while the older leaves remain green (yellowing in nitrogen-deficient plants starts with the older leaves).  Plants become dwarfed and spindly.  Most soils contain adequate sulfur, but if there is a lack, ammonium sulfate can be added.

Calcium promotes early root formation, improves general vigor, and increases resistance to disease.  Calcium deficiency causes distortion in young stems, and stem tips die.  Excess calcium can cause a deficiency (reduced intake) of potassium and magnesium.  Inadequate amounts of calcium can be corrected by spraying plants with calcium nitrate or adding calcium sulfate (gypsum) to the soil.  Follow the directions on the package.

Chlorophyll and sugar are formed with molybdenum, which is important for seed development and required by the nitrogen metabolism of all plants, although only in minute quantities.  Insufficient molybdenum leads to stunted, crinkled leaves that are pale green or yellow and malformed.  Remedy this deficiency by applying sodium or ammonium molybadate (1 pound per acre–about a teaspoonful per 1,000 square feet).  You can also plant vegetables and turn under at maturity.

Calcium utilization and normal cell division require boron, which also influences the conversion of nitrogen and sugars into more complex substances.  A deficient amount of boron is shown in the scorching of tips and margins of younger leaves.  Excess boron turns leaves yellowish red.  Boron deficiency can be corrected by spraying plants with a borax solution (1 teaspoon per gallon).

The availability of all nutrients needed for plant growth also depends on the soil’s pH, so keep that in mind when you consider the possible cause of a problem.  In addition, the amounts given here for correcting micronutrient deficiencies are minimum ones.  Severe deficiencies demand larger quantities of individual nutrients.  To determine exact amounts have the soil tested.

© Copyright by Karen Newcomb

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