The Basics of Fertilizing

TREES & SHRUBS

When it comes to trees and shrubs in your landscape, fertilizing is not necessarily an annual ritual. Many gardeners have the false impression that the more fertilizer they apply the more the plant will grow. Fertilizer is not plant food . Plants use water, carbon dioxide, elements from fertilizer, and energy from the sun to produce their own food. Synthetic (manufactured) and natural (some times incorrectly called organic) fertilizers provide nutrients for plant growth.

Adding the correct amount of fertilizer can promote healthy flower production and foliage growth while an excessive fertilizer application can decrease plant health and can lead to decline and death. Over application or incorrect application of fertilizer can contribute to polluting our rivers, streams, lakes, and estuaries. Excess fertilizer can increase the likelihood of some plant diseases. Fertilizing plants that have already outgrown their allotted space can only lead to more pruning. A moderate rate of growth and good, green color is desired for most woody plants. Excessive vigor, which is evident by lush, green leaves and long shoot growth is often undesirable. Such plants are more susceptible to injury by cold in winter, are more likely to be broken during wind and ice storms, and usually will require more pruning than plants making moderate growth.

All too often gardeners assume that if a plant is not doing well they should fertilize to correct the situation. Fertilization may be helpful but only after the problem causing poor growth has been corrected. Plants which are growing poorly will exhibit one or more of the following symptoms:
 

  • light green or yellow leaves 
     
  • leaves with dead spots 
     
  • leaves smaller than normal 
     
  • fewer leaves and/or flowers than normal 
     
  • short, annual twig growth 
     
  • dying back of branches at the tips
  • wilting of foliage

These symptoms of poor growth may be caused by inadequate soil aeration, moisture, or nutrients; adverse climatic conditions; incorrect pH; or disease. Recently transplanted trees and shrubs often will not resume a normal growth rate until the original root system is reestablished. Plants disturbed by construction within the past five to ten years may be in shock and exhibit limited new foliage growth. Do not assume that an application of fertilizer will quickly remedy any problem which is encountered, in many cases it can make existing problems worse. You should attempt to determine the specific cause in each situation and apply corrective measures.

Plant Nutrients
Plants require 17 elements for normal growth. Carbon, hydrogen, and oxygen are found in air and water. Nitrogen, potassium, magnesium, calcium, phosphorous, and sulfur are absorbed from the soil. The latter 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; these are called micronutrients or trace elements. The micronutrients include iron, zinc, molybdenum, manganese, boron, copper, cobalt, and chlorine. The nutrients that are most likely to limit plant growth are nitrogen, phosphorus, and potassium.

Nitrogen is a primary component of proteins and is a part of every living cell. This nutrient is usually more responsible for increasing plant growth than any other nutrient. Shortages can cause slow growth, reduced leaf size, yellowing, short branches, premature fall color and leaf drop, and increases the likelihood of some diseases. An over abundance can cause excessive shoot and foliage growth, reduced root growth, low plant food reserves, and increased susceptibility to environmental stresses and some plant diseases.

Nitrogen is a mobile nutrient it is in constant motion. Nitrogen applied to the soil can be used by plants, washed off the soil surface, lost to the air as a gas, or leached through the soil). Nitrogen from granular fertilizer can enter streams from surface runoff. Nitrogen loss is higher when a heavy rain immediately follows a surface application of fertilizer, especially on sloped areas. Incorporating fertilizer into the soil or lightly watering (1/4 to 1/2 inch) after making a surface application will reduce the amount of nitrogen loss.

Phosphorus (P) plays a role in photosynthesis, respiration, energy storage and transfer, cell division, and cell enlargement. It promotes early root formation and growth, and the production of flowers, fruits, and seeds. Many of our urban soils are low in phosphorus. Cultivated farm land often has a high phosphorus level from years of fertilization. In these cases, the addition of more phosphorus is not going to increase yields and can potentially harm the environment.

When applied as fertilizer, phosphorus is quickly bound by soil particles. Phosphorus is extremely immobile in soils (except sand); it moves about 1 inch from its original placement. Unless phosphorus is incorporated into the soil, watered in, or applied as a band, plants may not be able to use it.

Potassium in involved in many plant growth processes; it is vital to photosynthesis and helps regulate water in plants. Potassium fertilization helps plants overcome drought stress, increases disease resistance, and improves winter hardiness. Potassium can be leached through the soil by water, but not as quickly as nitrogen.

Nutrient uptake by plants
Nutrients in the soil can be in a solid form (granular fertilizer, organic matter), attached to the soil particles or dissolved in soil water. For an element to be absorbed by plants it must be in a form the plant can use, and present (dissolved) in soil water. Water and oxygen are required for nutrient movement into plant roots. Without adequate oxygen in the soil, there is limited nutrient absorption.

Anything that lowers or prevents the production of sugars in the leaves can lower nutrient absorption. If the plant is under stress due to low light or extremes in temperature, nutrient deficiency problems may develop even though adequate nutrients are available in the soil solution. Diseased or damaged roots, improper soil pH, water logged sites, and plantings that are too deep can result in inefficient nutrient absorption. Adding fertilizer under these conditions will not enhance plant growth, and may actually cause plant damage.

The stage of growth or how actively the plant is growing may also affect the amount of nutrients absorbed. Many plants go into a rest period, or dormancy, during part of the year. During this dormancy few nutrients are absorbed.

Fertilizer Terms
Fertilizer
: Any material used to supply one or more of the essential plant nutrient.
Fertilizer ratio: The relative proportion of N, P, and K. 16-4-8 fertilizer has a ration of 4:1:2 or 4 parts nitrogen to 1 part phosphorus to 2 parts potassium.
Balanced fertilizer: A fertilizer containing equal parts of each major element, i. e. 10-10-10. 
Complete fertilizer: A fertilizer containing nitrogen, phosphorus, and potassium. Examples of commonly used complete fertilizers are 10-10-10, 16-4-8, and 12-4-8.
Incomplete fertilizer: A fertilizer missing one or two of the major elements, i. e. 0-20-0.
Fertilizer analysis: The minimum amount of each element in a fertilizer as stated on the label. 
Weed and feed fertilizers: A combination of fertilizer and herbicide. They are often used on lawns to prevent certain weeds from germinating, or to kill existing broadleaf weeds.
Chelate: Chemical compounds that help hold metal ions (such as iron) in solution so the plant can adsorb them more readily.
High analysis: A fertilizers containing 30 percent or more active nutrients, i. e. ammonium nitrate 33-0-0. The cost per bag is usually more but the cost per pound of nutrient is less (therefore the cost for fertilizing a given area is less). 

Types of Fertilizers
All fertilizers are labeled with three numbers, giving the percentage (by weight) of nitrogen (N), phosphorus (P2O5), and potassium (K2O). A 100 pound bag of fertilizer labeled 0-20-10 has 0 pounds of nitrogen, 20 pounds of phosphorus, 10 pounds of potassium, and 70 pounds of filler. Filler is added to make the fertilizer easier to spread and to reduce the likelihood of burning plants with too much fertilizer. A fertilizer may contain secondary nutrients or micronutrients not listed on the label.

The diversity of fertilizer types and brands can be overwhelming when you go to make a purchase. Generally speaking, the timing and rate of application are more critical than which fertilizer you purchase. In regards to water quality, the most important issue is the type of nitrogen in the fertilizer you purchase. Most fertilizers contain nitrogen in a quick release form (10-10-10 and 8-8-8), others are in a slow release form (16-4-8, 12-4-8) some are a combination of both. Quick release forms of fertilizer are immediately available, but do not last as long and can cause plant damage if a large application is made.

Ammonium nitrate, ammonium sulfate, calcium nitrate, and potassium nitrate are all water soluble, quick release forms of nitrogen. The nitrogen becomes available as soon as it come in contact with soil water. Urea is an organic form of nitrogen but it is also quickly converted to nitrate nitrogen. High application rates combined with high irrigation or rain fall can result in large amounts of nitrogen being leached below the root zone.

A slow-release fertilizer releases nutrients at a rate that makes them available to plants over a long period. Slow-release fertilizers need not be applied as frequently as other fertilizers and there is less potential of leaching into ground water.

The initials W.I.N. and W.S.N. on fertilizer labels stand for water insoluble nitrogen and water soluble nitrogen, respectively. The water soluble nitrogen dissolves readily and is usually in a very simple form, such as ammonia nitrogen or nitrate nitrogen. Water insoluble nitrogen is referred to as a slow release nitrogen source. Nitrogen which will not dissolve readily is usually in an organic form of nitrogen (with the exception of urea) that must be broken down into simpler forms by soil microorganisms before it can be used.

Sulfur-coated urea is a slow-release fertilizer with a covering of sulfur around each urea particle. Different thicknesses of sulfur control the rate of nitrogen release. Watering does not affect its release rate. Sulfur-coated urea applied to the soil surface releases nitrogen more slowly than if incorporated into the soil. This material generally costs less than other slow-release fertilizers, and it supplies the essential element sulfur.

Some fertilizer products are coated with multiple layers of resin. When they come into contact with water, the layers swell and increase the pore size in the resin so that the dissolved fertilizer can move into the soil. Release rate depends on the coating thickness, temperature, and water content of the soil. There is often a large release of fertilizer during the first 2 or 3 days after application. Release timing can be from 0 to 12 months, depending on the coating.

Natural Fertilizers 
Natural fertilizer materials can serve as effective fertilizers, but only if their nutrient contents are known and their mineralization rates are estimated closely.  The advantages and disadvantages of natural and synthetic fertilizers relate to the consumer, not to the plant.

Natural fertilizers are mostly complex chemical substances containing carbon. In general, natural fertilizers release nutrients at a slow rate over a fairly long period. This can be advantageous for perennial crops, since only one large application may be needed.

Most natural materials are far less predictable in nutrient content, nutrient release, and nutrient efficiency than commercial grade fertilizers. Before most organic nutrients can be absorbed by plants, they have to be broken down to an inorganic form by soil microorganisms through a decaying process called mineralization. This process is affected by moisture, temperature, and the microbial species and populations in the soil. Most organic materials are effective only when the soil is moist and soil temperature is warm enough for the soil organisms to be active. They may not release enough of their principal nutrient at a time to give optimum plant growth. 

When packaged as fertilizers, natural fertilizers will have the nutrient analysis stated on the labels. Some organic materials, particularly composted manures and sludges, are sold as soil conditioners and do not have a nutrient guarantee (small amounts of nutrients may be available). Most natural fertilizers are high in only one of the three major nutrients; many are low in all three.

Natural fertilizers can be expensive if applied in amounts adequate to supply nutrients for good plant growth; however the value for improved soil structure should be considered. The nutrient content may need to be supplemented with other organic or inorganic materials to achieve a balanced ration of nutrients.

How much to use varies with the nutrient content of the material. The age of the material is also a factor; when organic material decays and is rained on, they lose nutrients, especially potassium and to some extent nitrogen. Fresh manures may cause plant injury, especially when large quantities are used.

Examples of Natural Fertilizers
Dried blood is a byproduct from beef processors. As blood is drained from recently killed animals, it is dried and ground into a powder. It is a rich source of nitrogen and supplies certain essential trace elements including iron. The gardener must be careful not to use more than the amount recommended on the label. 

Fish emulsion
 is a partially decomposed blend of finely pulverized fish. The odor is intense, but dissipates within a day or two. Fish emulsion contains up to 5 percent readily available nitrogen and is a source of several trace elements. Contrary to popular belief, too strong a solution of fish emulsion can burn plants, particularly those in containers.

Animal manure is also a complete fertilizer but is low in nutrients. Manures vary in nutrient content according to the animal source and what the animal has been eating. A nutrient ratio of 1-1-1 is typical. The amount of nitrogen in manure varies but is normally around 0.5 percent (poultry litter is higher in nitrogen). This is 1/20 of the nitrogen found in an equal amount of 10-10-10 fertilizer. Commonly available manures include horse, cow, chicken, and sometimes sheep. The actual nutrient content varies widely: the highest concentration of nutrients is found when manures are fresh. As it is aged, leached, or composted, nutrient content is reduced. Fresh manure should not be used where it will contact tender plant roots. Manures are good soil conditioners. Manures should be incorporated into the soil to conserve nitrogen. If left on the soil surface, up to 25 percent of the ammonia nitrogen can be lost within 2 days and 75 percent or more can be lost within 1 month after application.

Rock phosphate is ground rock that contains as much as 30 percent phosphate. It is not in a readily available form and is released very slowly.

Granite dust contains about 5 percent potassium but little of it is available for plant growth.

Greensand contains 6 percent potassium. It is also available very slowly.

Wood ashes are often used as a soil amendment. They contain potash (potassium), phosphate, boron, and other elements. Wood ashes can be used to raise soil pH; use twice as much wood ash as limestone for the same effect as lime. Ashes should not come into contact with germinating seedlings or plant roots as they may cause root damage. Spread a thin layer during the winter and incorporate into the soil in the spring. Check pH yearly if you use wood ashes. Never use coal ashes or large amounts of wood ash (no more than 20 pounds per 1,000 square feet), as toxicity problems may occur.

Fertilizing Newly Installed Plants
Wait until spring to fertilize fall planted trees and shrubs. Wait six to eight weeks to fertilize plants installed in the spring. Apply a slow release fertilizer in a light band along the perimeter of the planting hole. Remember that newly installed plants are under stress and should receive only a light application of fertilizer. For 1 gallon container plants, apply 1 teaspoon of a nitrogen fertilizer or 1 tablespoon of 10-10-10. For larger plants apply 2 to 3 tablespoons.

Fertilizing Established Plants
Fertilization rates should be based on plant age, current and desired growth rate, plant type, or by using general guidelines. The rate should also be influenced by rainfall and soil type. A wet season will normally increase the need to fertilize especially in sandy soils. During periods of dry weather, reduce the amount of fertilizer. Fertilizer encourages water-demanding new growth and can injure roots of ornamentals under drought stress.

Growth rate - The amount of new growth can be used as a guide to determine fertilizer needs. When new shoots are more than 6 inches long in one season, fertilizer is normally not required. When new shoot growth is between 2 and 6 inches long, fertilizer is optional. When plants exhibit poorly colored leaves, smaller than normal leaf size, or premature fall color or leaf drop the plants may need additional fertilizer. These signs may also indicate some type of root problem. Deficiency symptoms do not give an indication of how much fertilizer is needed --- only that fertilizer is needed.

Age - Newly installed plants should be given time to reestablish their root system before trying to push new growth with high nitrogen fertilizer. If you are trying to push the growth of a young hedge you may wish to make several light applications of fertilizer per year (March, May, July). As woody plants mature, the need for nitrogen decreases; rapid growth is no longer needed or desired. Most established woody plants perform well with just one application per year.

Type of plant/location - Plants growing in a restricted root zone will need less nitrogen. Plants with a fibrous root system, such as azalea, rhododendron, and blueberry, are very easily damaged by fertilizer. Light applications are recommended. Plant roots normally grow three times as far as their branches. Ornamentals located near a lawn that is fertilized regularly may not need additional fertilizer since many of their roots extend into the lawn area where they will absorb nutrients. It might be all that an established plant needs.

General guidelines -
 Normally 2 to 4 pounds of a complete fertilizer per 1,000 square feet per year is recommended for optimum growth. If your are trying to push new growth use the higher rate. To determine how much of a particular fertilizer to apply, divide the percent nitrogen into 100 and multiply times the amount of nitrogen recommended. For example, the amount of 12-4-8 needed to apply 1 pound of actual nitrogen per 1,000 square feet is obtained by dividing 100 by 12 and multiplying by 1. Thus 8.3 pounds of 12-4-8 should be applied per 1,000 square feet.

For small trees and shrubs use 1/2 to 1 cup of 10-10-10 fertilizer. The amount of fertilizer should not exceed 1 tablespoon per foot of height for fertilizers containing 10 or more percent nitrogen. Do not apply more than 3 pounds of actual nitrogen per 1,000 square feet. For large trees measure the diameter 4 feet from the ground and apply 0.1 pound actual nitrogen (0.1 pound of actual nitrogen equals 1 pound of 10-10-10, 0.3 pound of ammonium nitrate (33-0-0), or 0.2 pounds of 5-10-10) for each inch of trunk diameter. If the area under the tree is known, simply broadcast 0.1 pound of actual nitrogen per 100 square feet.

Unless a soil test indicates otherwise use a fertilizer containing 10 to 16 percent nitrogen. Fertilizers such as 16-4-8 and 12-4-8 have the ideal ratio for woody plants, however, fertilizers such as 10-10-10 or 8-8-8 can be used. At least 30 percent of the nitrogen should be in the ammoniacal or urea form. They are slower to release nitrogen than those in a nitrate form.

Time and method of application
A nitrogen fertilizer application will have its greatest effect three to four weeks after application. Woody plants can absorb nutrients as long as the soil temperature is above 40F. Root growth occurs during cool weather even when the foliage appears dormant. Root growth of woody ornamentals is most active in fall and late winter/early spring but slows during hot, summer weather.

Fertilize trees and shrubs in the spring or fall. Spring fertilizer application should be made before new growth starts. Fall fertilization should be made approximately one month after the first killing frost. Many gardeners are reluctant to fertilize in late fall for fear it will stimulate new growth if a period of unseasonably warm weather occurs. Fertilizer applied in late fall is more effective in promoting plant growth than spring applied fertilizer.

Fertilization in late summer (mid August) should be avoided since it may stimulating late growth that will not harden off before frost. Remember when applying slow-release fertilizers around trees or shrubs to not apply late in the season (after July 15) because they may keep the plant growing rapidly late in the summer. The late season growth may not "harden off" completely, and winter damage may occur.

The fertilizer should be spread evenly over the entire root zone which can extend two to three times the width of the branches. Remember that some of the root zone may have already been fertilized when fertilizer was applied to the lawn or flower bed. Sprinkle the fertilizer on top of the soil or mulch and water lightly. Since the fertilizer will quickly move through the mulch there is no need to remove it or to place the fertilizer below it. Spread the fertilizer evenly under the branches. Dumping fertilizer in one spot can caused the roots below the fertilizer to be burned and die. Apply fertilizer when the foliage is dry so the fertilizer does not stick to plant foliage and cause burning. If fertilizer lodges in the whorls of plant foliage, use a broom to brush the fertilizer off.

The practice of placing fertilizer in holes around mature trees has been tested and research indicates that surface application of fertilizer is sufficient since most of the feeder roots are in the top foot of soil. If the soil is compacted you can bore holes 4 to 6 inches deep, 2 to 3 feet apart using a punchbar or a drill with a 2-inch auger. Start 2 feet from the trunk and continue to 2 feet beyond the branches. Divide the fertilizer into as many equal parts as there are holes and place in the holes. Boring holes in soil can increase soil aeration and water penetration into the root zone.

Fertilizer spikes and stakes that are driven into the ground contain satisfactory amounts of nutrients. Unfortunately, the spacing is such that very little fertilizer comes into contact with most of the root system. Lateral fertilizer movement in the soil is very limited.

Foliar sprays of a liquid or water soluble fertilizer on the foliage can be used for correcting deficiencies of minor elements such as iron or manganese. This method should not be used to provide all of a plant's fertilizer needs. The benefits of foliar sprays are short lived. Since nutrients deficiency are often caused by a disease or improper soil condition (pH, drainage, soil compaction) foliar sprays give only temporary relief and do not correct the main problem.

Tree injections of micronutrients is another method of fertilization that should be used only as a means of last resort. Trees can be permanently injured by drilling holes and the decay that could develop may out weight any benefit the fertilizer might provide. Any benefit from the fertilizer will be temporary at best.

Do not use weed-and-feed fertilizers under trees or shrubs unless the label says it is safe. Some plants, such as dogwoods, are very sensitive to dicamba herbicide that is contained in many weed-and-feed lawn fertilizers.

VEGETABLE and FLOWER GARDENS

Plants grow using energy from the sun combined with nutrients taken from the soil. Because the organic matter in soil holds nutrients like a sponge until they are needed by plants, soil that is fertile, well drained, and regularly enriched with compost often holds a reasonable supply of plant nutrients. Unimproved, newly cultivated soil is usually low in organic matter, so it is also low in nutrients.

All edible plants remove some nutrients from the soil, and some have such huge appetites that they quickly exhaust the soil (and then produce a poor crop) without the help of fertilizer. Fertilizer is especially helpful early on, when plants are making fast new growth. You can mix fertilizer into individual planting holes, work it into furrows, or use a turning fork to mix it into beds. You also can use liquid fertilizers, but granular products last longer in vegetable gardens.

Always follow the rates given on the fertilizer label when deciding how much to use. Too much fertilizer can be worse than too little! Overfed plants often grow huge, yet bear a light crop late in the season.

With experience, you will learn how to match fertilizer amounts with plants' needs for your climate and soil. Onions, tomatoes, sweet corn, and vegetables grown in containers respond to special fertilizing techniques, but most crops grow well if you simply mix a balanced fertilizer into the soil as you set out the plants. Use the lists below to help estimate the fertilizer needs of your favorite crops.

Light feeders often benefit from a small amount of starter fertilizer but require no additional feeding when grown in soil that has been enriched with compost:

  • Bush beans
  • Mustard greens
  • Peas
  • Southern peas
  • Turnips

Moderate feeders often need good drainage and moisture-holding mulch more than they need fertilizer. Avoid using organic fertilizers made primarily from processed manure when preparing the soil for beets, carrots, and other root crops. Manure can contribute to scabby patches on potato skins and forked roots in carrots and parsnips.

  • Beets
  • Carrots
  • Okra
  • Pole beans
  • Potatoes
  • Sweet potatoes

Heavy feeders are often highly productive plants, so a few minutes spent mixing in fertilizer before you set out plants is time well spent. Just don't go overboard by applying too much! Plants often grow slowly in cool spring weather, so wait until the weather warms to decide that the application rate given on a fertilizer's label was not enough. Some heavy feeders also respond to second helpings later in the season.

  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Cantaloupe
  • Cauliflower
  • Corn
  • Cucumbers
  • Eggplant
  • Kale
  • Kohlrabi
  • Onions
  • Peppers
  • Rhubarb
  • Squash
  • Tomatoes
  • Watermelon

 

 

HOLLY ACRES NURSERY
AND GARDEN CENTER
We Accept Cash & Credit Cards

Delivery Available

ONLY 3.9% Sales Tax

5403 HWY 86   ELIZABETH, CO   80107    303-646-8868

 

Home   ORDER NOW Map & Directions
TREES SHRUBS FRUIT TREES
NEW!
ROSES
VEGETABLES AND SMALL FRUITS
PERENNIAL
 PLANTS
 
CONTAINER PLANTS AND ANNUALS
 
GARDEN
STATUARY
 
Christmas Trees & Events
Strike it Rich

christmas trees colorado