Plant Nutrition Management In The Garden


Apply only the nutrients

plants can use.


In your garden

Optimal plant growth requires 16 vital nutrients broken down into two categories, Macronutrients, and Micronutrients:

  • Macronutrients:

    • calcium (Ca), carbon (C), hydrogen (H), magnesium (Mg), nitrogen (N), oxygen (O), phosphorus (P), potassium (K), sulfur (S)

  • Micronutrients/trace minerals:

    • boron (B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn)

Nitrogen, phosphorus, and potassium (NPK) are primary Macronutrients. Vegetative growth connects with nitrogen, flowering and fruiting with phosphorus, and durability and disease resistance with potassium. Large amounts of primary macronutrients are needed.  Hence the reason these numbers are the ones represented on fertilizer bags.

The Secondary Macronutrients are calcium, sulfur, and magnesium.  The strength of the cell wall and the process of photosynthesis are directly related to Calcium and Magnesium.  Sulfur is a constituent of specific amino acids.

Small amounts of micronutrients are necessary. These nutrients are already present in the soil.

Stellar plant growth needs both macro and micronutrients.   Over-application of fertilizer can hinder this by being a detriment. Applying excess plant nutrients will impair plant growth.  Also, excess fertilizers could potentially contaminate the groundwater leaching their way through the soil.

Testing Soil 

If you want to know the nutrients and pH, it is essential that you test your soil. That will provide your plants with the proper balance of nutrients while avoiding over-application.  When establishing a new garden have the soil tested.

Don't let the minor cost of soil testing be a reason not to get it done.  The test will be lower in price. Than that of plant materials and labor. Correcting a problem before planting is much more straightforward and cheaper than afterward. Even after you have an established garden continue to take periodic soil samples.  Doing so will help ensure you continue to have a productive garden.

While many people routinely lime their gardens but doing so can lead to high pH levels. Many fertilizers tend to lower the pH, so the pH may drop below desirable levels after several years, of constant fertilization don't be surprised if your pH is all out of whack. Home tests for pH and the primary macronutrients are available at your garden center.  These test will give you a glimpse into whats going on with your soil.  For a few bucks more than what you pay the home test and a little bit of your time, you can send the sample off to your local extension service and receive a full biopsy of your soil.

University testing services will provide more detail than you can receive from a home test kit.  Request individual tests for micronutrients if you suspect a problem. Accompanying the analysis of nutrients in your soil, you will provide recommendations for the application of nutrients or on adjusting the pH.

Testing soil pH is straightforward– pH is a measure of how acidic or alkaline your soil is. When you do a soil test, it will show one of three results:

1. a pH of seven is considered neutral

2. a PH below seven is acidic

3. above seven is alkaline

pH dramatically influences plant nutrients.  Adjusting the pH, When nutrient deficiencies are suspected will often correct the problem. At pH above seven, a plant has trouble uptaking micronutrients because they become less available. Iron deficiency is a common problem regardless of the soil pH. At pH below seven, plant toxicity can occur due to the fact of other micronutrients being too available. University and Commercial labs regularly test for Phosphorus and potassium.

Soil tests for nitrogen are less reliable than for other nutrients. Several forms of Nitrogen are present in the soil.  The atmospheric conditions determine the shape the nitrogen will take.  These variance transformations make it hard to receive a precise analysis of nitrogen. For this reason, Most soil test labs do not test for nitrogen. Nitrogen readings from Home testing kits may not be reliable.

Organic matter is often part of a soil test. Soil organic matter is highly desirable. Organic matter has a considerable influence on soil structure. Good soil structure improves aeration and water movement and retention.  Improving these factors leads to increased microbial activity on all levels of the soil food web.   Which in turn leads to better root growth, which influences the availability and uptake of nutrients for plant growth. Soils rich in organic matter have a higher supply of available plant nutrients.

Tests for micronutrients are usually not performed unless there is a reason to suspect a problem. Some plants have increased requirements for specific micronutrients and may show deficiency symptoms. Iron deficiency is common on blueberries unless the soil is quite acidic. On this greenery, the younger leaves will usually show signs of the defect first. The areas between the threads will have a yellow color while the veins stay green. The other produce planted in the ground will probably not show any signs of lacking. If you changed the pH, it should fix the problem.


How to take a Soil Test


  1. If you want to send in your sample to the land-grant university in your state, you will need to contact the local Cooperative Extension Service (they will give you the information you need and sample bags). Another option is to send your sample to a private testing lab. Again you would need to contact the lab for specific details.

  2. You will need to follow directions accurately to get the best results. Here is a basic guideline on how to take a proper soil sample.

    1. Collect the sample. The best sample is moist, not wet.

    2. Testing an acre of land requires 10 to 15 sub-samples. Take Samples from each area. For example, submit a separate sample for your garden soil and your lawn soil.

    3. Get a clean and transparent container to hold the sample.

    4. Clear and clean the area from which you will get the sample.

    5. With a spade or soil auger, dig a small amount of soil to a depth of 6 inches.

    6. Put the soil in your clean container.

    7. Collect samples until the neccessary amount is achieved.

    8. Mix the samples very well.

    9. From the thoroughly mixed mixture, select the sample that will get mailed to be analyzed.

    10. It is imperative to send the sample immediately! Do not dry before mailing.

  3. For a home soil testing kit, follow the directions in the package. Use the steps above as a guide.


Applying Fertilizers and soil amendments

 Once you have the soil test analysis, you can add nutrients or soil amendments as needed. Use lime to raise the pH. Lime is most effective when mixed into the soil, apply before planting. For large areas, rototilling is most useful, but this will destroy the microorganisms within the food web. For small areas or around plants, work the lime into the soil. Do not dig too deeply when working around young plants this can damage the root zone.

Soil conditions and the form of lime used dictate how quickly the pH of the area changes. Lowering the pH is not an instantaneous procedure,  it may take several months before a significant difference is noted. Soils high in organic matter and clay need a higher amount of lime to change the pH than do sandy soils. Other commercially available fertilizers will also help reduce the pH.

Follow the soil test or manufacturer’s recommended rates of application.  Don't forget about the problems overfertilization brings. Mix amendments well into the soil. There are numerous choices providing nitrogen, phosphorus, and potassium. If your ground is of adequately fertile, applying compost may be the best method of using additional nutrients.

Compared to commercial fertilizers Compost is relatively low in macronutrients.  It is especially beneficial in improving the condition of the soil and feeding the microorganisms within the soil food web. The enriched soil is the ideal habitat for earthworms and other beneficial soil microorganisms.  These elements are essential for releasing nutrients for plants to use. By keeping the dirt loose and enriched with compost allows plant roots to grow well throughout the ground, extract and obtain nutrients from larger areas.

Manure is also an excellent source of plant nutrients and organic matter. Compost this fertilizer before applying. Fresh manure may be too potent and can injure plants. Be careful when composting manure. If left in the open, exposed to rain, nutrients may leach out, and contaminate waterways. The location of the stored manure is imperative.  Do not store near wells and waterways. Improperly applied fertilizer also can be a source of pollution. To achieve optimal results and benefits work composted manure into the soil.  Work compost and manure into the soil to a depth of 8 to 12 inches when preparing a new bed.

Another way to incorporate organic matter and plant nutrients are by growing green manures; crops grown, tilled and left in the soil.  They break down, providing nitrogen and other plant nutrients. Green manures may also provide additional benefits of reducing soil erosion. Grow Green manures such as rye and oats in the fall after the crop harvest. In the spring, till the green manures into the bed during the bed preparation stage.

When using organic sources of nitrogen, a chemical reaction must take place for the nutrients to be accessible.  The natural form is inaccessible to plants. Therefore, it is beneficial to have well-drained, aerated soils that provide the favorable habitat for the soil microorganisms responsible for these conversions. Numerous sources of commercial fertilizers supply nitrogen, phosphorus, and potassium.

The first number on the fertilizer analysis is the percentage of nitrogen, the second is phosphorus, and the third is the potassium content(NPK).  If you see double digit numbers, the fertilizer is synthetic. The quantity of each nutrient necessary depends on your soil test results and the plants you are fertilizing.

As mentioned before, nitrogen stimulates vegetative growth while phosphorus stimulates flowering. Too much nitrogen can inhibit flowering and fruit production. Vegetables prefer a fertilizer higher in phosphorus than nitrogen such as a 5-10-5.

Commercial fertilizers are applied as a dry granular material, or diluted with water and distributed to the growing area. While using granular materials take necessary precautions to avoid spilling on sidewalks and driveways. These water-soluble crystals have the potential to pollute the storm sewers and water supply. Granular fertilizers are salt based.  If applied too liberally, salt causes damage to the root zone and can inhibit the uptake of nutrients. When using a liquid fertilizer, apply directly to or around the base of the plant.

Dormant plants require minimal nutrients.  Nitrogen encourages vegetative growth so applying in the fall may reduce the vegetation’s ability to harden for winter.  In the case of phosphorus, the nutrients become unavailable or locked up to the plants once spread on the soil.Reduce the amount of fertilizer applied by individually fertilizing plants as opposed to broadcasting over the entire garden For better uptake, apply the fertilizer in a band near the viable growth. Do not use directly on or in contact with the roots.


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