Plant Nutrition

Plant Nutrition

Plants need 17 elements for normal growth. Carbon, hydrogen, and oxygen are found in air and water. Nitrogen, potassium, magnesium, calcium, phosphorus, and sulfur are found in the soil. The above six elements are used in relatively large amounts by the plant and are called macronutrients. There are eight other elements that are used in much smaller amounts and called micronutrients or trace elements. The iron, zinc, molybdenum, manganese, boron, copper, cobalt and chlorine. All 17 elements. Both macronutrients and micronutrients are essential for plant growth.

Fertilizer Analysis

All fertilizers are labeled with three numbers. These three numbers give the percentage by weight of available nitrogen, phosphate, and potash in the bag or box.

Nitrogen is important for leaf and stem growth and provides the rich green color in a plant.

Phosphorous (derived by the plant from phosphate) provides for root and flower growth.

Potassium (derived by the plant from potash) helps build plant tissue and aids in the production of chlorophyll.

A fertilizer is said to be complete when it contains nitrogen, phosphorus and potassium.

In a 10-pound bag of 5-10-10 there is ½ a pound total nitrogen, one pound available phosphorus, and one pound soluble potash. A fertilizer of high analysis such as 10-10-10 is more expensive per 10 pounds than a fertilizer of low analysis such as 6-8-8, but less of the high analysis fertilizer is used per 1000 square feet of garden, and it is often the best buy.

Both synthetic and commercial organic fertilizers must display these numbers; synthetic fertilizers are usually (but not always) higher in nutrients by weight. In general, synthetic fertilizers act more quickly than organic types, though some organic materials release their nutrients quite rapidly.

Slow-release fertilizers release nutrients (make them available to the plant) over an extended period. Caution is needed when slow release fertilizers are applied around perennials, trees or shrubs, as the later nutrient release may keep the plants growing into the fall when they should be hardening off for the winter. Blood meal, bone meal, fish emulsion and all manures are examples of organic fertilizers. Organic fertilizers usually contain relatively low concentrations of actual nutrients, but they perform other important functions which the synthetic formulations do not. These functions include: increasing organic content of the soil, improving physical structure of the soil and increasing bacterial and fungal activity.

It isn’t possible, therefore, to say absolutely whether it is better to go all organic or all synthetic fertilizers. Organic materials such as manures and plant waste do usually help improve the soil structure while adding nutrients while chemical fertilizers do not affect soil structure. General purpose synthetic fertilizers have the advantage of being readily available to the gardener and relatively inexpensive. Many customers use a combination of the two.

Effects of Over-Fertilizing

Fertilizers are salts, much like our familiar table salt except that they contain various plant nutrients. If tender plant roots are close to the fertilizer granules, water is drawn from these roots. Plant cells in these roots begin to dehydrate and collapse, and the plant roots are ‘burned’ or dried out to a point where they cannot recover. It is important to apply fertilizer according to instructions.

To prevent water quality problems, avoid getting fertilizer on sidewalks and driveways where it can easily wash into storm drains and, eventually, into creeks, streams, and rivers. Nutrients, particularly nitrogen, become a water quality problem through leaching or run-off. Leaching is the effect of nutrients being washed through the lower soil layers and into the groundwater supply. Leaching and run-off not only rob your soil of nutrients, but also lead to erosion.

How much do I need?

The best way to determine exactly what fertilizer your sol needs is to have the soil tested every 3-4 years. This is especially important for your vegetable garden and lawn. Soil testing is available through your local Dep’t of Agriculture at the Agreena (Coliseum), through private labs or with soil test kits which can be purchased from our garden center.


Dry Fertilizers and Manures

In the fall or in the spring before working the soil, measure out the correct amount of fertilizer and spread it evenly over the ground. You can toss it from a pail by hand or use a spreader. Thoroughly mix dry fertilizers into the upper six inches of soil. Be sure to wear gloves to protect your skin from irritating chemicals. Always follow the directions on the label for rate of application of all fertilizers and add the correct amounts. Too much fertilizer will harm plants and pollute the environment, especially through run off into water systems. It is also a waste of money. Organic materials may be used in combination with, or instead of, chemical fertilizers. In any case, it is important to calculate the total available nutrients in order to be certain that the plant is being supplied with adequate nutrient levels.

Slow-acting fertilizers, manures and compost are best applied in the fall to give them some time to start breaking down.

Liquid Fertilizers and Foliar Feeding

Fertilizer solutions are often used to water-in transplants, providing a readily available supply of nutrients for fast root growth and plant establishment. Liquid fertilizers may also be applied to plant foliage where the nutrients are absorbed directly through the leaf surface. This foliar feeding provides nutrients to the plant very quickly. There are several choices of fertilizers for liquid application. Commercial soluble fertilizers, such as RX-15, transplant starters or house plant formulations, are readily available and easy to use. (Granular fertilizers are not satisfactory because the phosphorus is not soluble.) Fish emulsion and liquid kelp (a seaweed) are good commercial organic sources. Follow label directions for each of these.

Liquid feeding is appropriate for container plants and smaller gardens to supply needed nutrients throughout the growing season. Unless you have a hose end sprayer specific for your fertilizer it’s a lot of work to use water soluble fertilizer on big areas. For larger areas, liquid feeding is more a one-time procedure, either as a transplant starter or as a foliar feeding to correct a deficiency in a major or trace element. If a foliar feeding is desired, follow directions carefully. Using too much fertilizer, especially the synthetic forms, can quickly burn the foliage. A very fine mist sprayer is usually required.

Fertilizers and PH

The degree of acidity or alkalinity of the soil, as measured by pH, is an important factor in the availability of soil nutrients to plants. At pH extremes, some nutrients become partially or completely locked up in the soil and cannot be used by plants even though they are still present. For example, in a soil with a pH near 8.0, potassium, nitrates, phosphates, iron, and manganese all become unavailable. At 4.5 or below, plants cannot get nitrates, magnesium or phosphates. Other elements may become so readily available that they are toxic to plants, as happens with aluminum at very low pH. Most vegetables do best between pH 5.9 and 7.0. Lime is often added to increase the pH to a desirable level. However, the addition of lime does not eliminate the need to add fertilizer.


Nitrogen (N) – Part of proteins, enzymes, chlorophyll, and growth regulations. Deficiencies: Reduced growth, yellowing (chlorosis), reds and purples may intensify with some plants, reduced lateral breaks. Remarks: Excess will yield all leaf and stem growth, with little fruit.

Phosphorus (P) – Role in fat, carbon, hydrogen, and oxygen metabolism; respiration and photosynthesis. Deficiencies: reduced growth, color may intensify, foliage turning brown or purple in some plants; thin stems, loss of lower leaves, reduced flowering. Remarks: In very acid or alkaline soils, phosphorus will be unavailable.

Potassium (K) – Important in starch formation, sugar translocation, water relations, disease resistance chlorophyll development, and tuber formation. Deficiencies: Reduced growth, shortened internodes, marginal burn or brown leaf edges, dead spots in the leaf, reduction of lateral breaks, and tendency to wilt readily. Remarks: Large amounts of potash are needed by most plants.

Magnesium (Mg) – Part of chlorophyll, enzyme activator, important in energy utilization. Deficiencies: Reduction in growth, yellowing between veins, also can occur with middle or lower leaves, reduction in seed production. Remarks: Interferes with calcium uptake if used in excess.

Calcium (Ca) – Important in cell wall structure, cell division, enzymes, and as an enzyme activator. Deficiencies: Inhibition of bud growth, death of root tips, cupping of mature leaves, weak growth. Remarks: Too much calcium will result in high pH, causing many of the micronutrients to become unavailable to the plant.

Sulfur (S) – Part of protein, amino acids, vitamins: important in respiration. Deficiencies: Symptoms are a general yellowing of the affected leaves of the entire plant. Remarks: In New Brunswick, acid rain discharges of sulfur to our soils are significant enough to affect us all.

Trace Elements

In addition to nitrogen, phosphorus, and potassium, plants must have trace, or minor, elements for good growth. These are needed in very small quantities, and most soils with lots of organic matter added on a regular basis already contain sufficient supplies. With good soil-building practices, trace elements do not generally present a problem to the home gardener. Synthetic fertilizers are relatively pure chemicals and most do not carry the trace elements normally present in organic fertilizers. Therefore, addition of trace elements through purchased or other organic materials such as manure, compost, green manures, and mulching, etc. is recommended. An exception to this is our high-quality line of Nutrite Fertilizers which do contain trace elements and an organic base. Also, our line of water-soluble fertilizers contains trace elements.

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