It doesn’t take an Einstein to have a successful garden, but some basic arithmetic can assist any gardener. Any time fertilizer, soil amendments, or pesticides are applied to the garden, it is important that the correct amounts be calculated so the applied material will help, not hurt, the plants. The following example will illustrate proper garden calculations.

Mr. MacGregor has a garden that is 30 feet long and 20 feet wide. His soil test recommendations are to apply 2 pounds of actual nitrogen per 1000 square feet. Using his new watering system, he wishes to apply one inch of water per week. His cabbage plants occupy an area 5 feet wide and 12 feet long, and while they are fenced so that rabbits can’t get them, cabbage loopers can and he would like to spray them with pesticide.

First Mr. MacGregor must calculate his garden area by multiplying length by width: 30 ft. X 20 ft. = 600 sq. ft. If his garden had been irregular in shape he could have divided it into rectangular sections, calculated the area of each section, and added them together.

To calculate the amount of fertilizer to spread over the garden, Mr. MacGregor checks the analysis of his fertilizer of choice. He is using 5-10-10. The first number in this analysis gives the percentage nitrogen by weight, or 5%. He divides the amount of actual nitrogen desired by the percentage, expressed as a decimal (1% = .01, 5% = .05, 15% = .15, etc.): 2 lbs divided by 0.05 = 40 lbs. for a 1000 square foot garden. Since Mr. MacGregor’s garden in 600 square feet, or six tenths of 1000 sq. ft., he multiplies the amount of fertilizer required for 1000 sq. ft. (40 lbs.) by six tenths, resulting in the proper amount for his garden, or 24 lbs.

His irrigation system has an easy-to-read in-line meter which indicates that the system uses 10 gallons of water per minute (gpm). An inch of water is equivalent to 28,000 gallons of water per acre. An acre is equal to 43,560 square feet. In gallons per square foot, that is 28,000 gal / 43,560 = 0.642 gal/sq ft. This can safely be rounded to 0.65 gal/sq ft, and for Mr. MacGregor’s garden, the result: 0.65 gal/sq ft X 600 sq ft = 390 gallons. At 10 gpm, that will require: 390 gal / 10 gpm = 39 minutes. Mr. MacGregor’s neighbor uses the low-tech but equally accurate, and simpler, method of measuring the water falling on her garden from a sprinkler with a rain gauge.

Standard spray applications require about 1 quart of spray for 125 sq ft of area. Mr. MacGregor’s cabbage occupy 5 ft X 12 ft = 60 sq. ft., so he will require 60 sq ft / 125 (sq ft/qt) = 0.48 qt. This can be rounded to 0.5, or 1/2 quart. The label states that 4 tablespoons of concentrated powder are used to prepare one gallon. One gallon equals 4 quarts, so: 1/2 qt. spray X 4 T/gal divided by 4 qt. = 1/2 tablespoon concentrated powder to mix 1/2 quart spray.

Too little water, fertilizer, or pesticide can result in garden problems. Too much can cause even worse problems, and costs extra money as well. Careful garden calculations will ensure that garden inputs have their desired effects.

(Prepared by Ellen Silva, Extension Technician, Consumer Horticulture, Virginia Tech, Blacksburg, VA 24061-0327.)

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Autumn is the time to prepare a safe holding area for unused supplies of gardening pesticides and fertilizers. Proper storage is important for many reasons, including preservation of the environment, protection of human health, and maintenance of chemical efficacy. A winter storage area or facility should:

be secure
be well-ventilated
be well-lit when in use
allow materials to remain “high and dry”
be protected from extreme heat and cold
be spacious enough to allow for separation of herbicides, fungicides, insecticides, and fertilizers
be enclosed in such a manner that leaks and/or spills may be contained and cleaned without compromising the soil and water quality in the vicinity.
The storage area must be secure from unwanted visitors, both people and animals! Good lighting and ventilation are important to the personal health of the user(s) of the facility. In addition, proper ventilation can prevent volatile chemicals from contaminating other materials in storage. Separation of chemicals in storage by type is additional insurance against contamination. Flammable liquids must be stored outside living areas and away from ignition sources. Dampness is a serious problem, as it reduces the shelf life of many chemicals and causes metal and paper containers to degrade. It is imperative that storage areas be secure from flooding. Temperature extremes can also affect product shelf life. In addition, heat increases the volatility of stored chemicals while freezing can cause some types of containers to rupture. If specific temperature ranges are required for proper storage, they will be found on the product label. Finally, the site must allow for containment of spills and/or leaks. Ideally, clean-up materials (absorbents, water) will be near at hand.

Chemicals and the containers in which they are to be held must be in good condition. Whenever possible, pesticides and fertilizers should be kept in their original containers. In all cases, a legible product label must be attached to the chemical container. Never transfer excess pesticide or fertilizers to an empty food container. Do not store pesticides with or near food, medicine, or cleaning supplies. An updated storage inventory allows for keeping track of what has been placed in storage and also helps in planning purchases next season. Useful records may include product name, active ingredient, date of purchase, and date and volume stored.

One way to minimize storage problems is to plan ahead, and buy pesticides and fertilizers one season at a time. The small-volume containers that seemed expensive in the spring may, in fact, be the “best buy” in the long run.

(Originally published by Pat Hipkins, Chemical, Drug, and Pesticide Unit, Virginia Tech, in The Virginia Gardener Newsletter, Volume 9, Number 11.)

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When used in reference to fertilizers, the word organic generally means that the nutrients contained in the product are derived solely from the remains or a by-product of an organism. Cottonseed meal, blood meal, fish emulsion, manure and sewage sludge are examples of organic fertilizers. Urea is a synthetic organic fertilizer, an organic substance manufactured from inorganic materials.

When packaged as fertilizers, organic products have the fertilizer ratio stated on the package label. Some organic materials, particularly composted manures and sludges, are sold as soil conditioners and do not have a nutrient guarantee stated on the package, although small amounts of nutrients are present.

Some organic fertilizers are high in one of the three major nutrients (nitrogen, phosphorus, or potash,) but low or zero in the other two. Some are low in all three macronutrients. A few organic products can be purchased “fortified” for a higher nutrient analysis. The ingredients used to fortify organic fertilizers are organic materials; for example, rock phosphate to increase phosphorus, or greensand to increase potash.

Organic fertilizers depend on soil organisms to break them down to release nutrients; therefore, most are effective only when soil is moist and warm enough for the microorganisms to be active. Nutrient release by microbial activity, in general, occurs over a fairly long time period. One potential drawback is that the organic fertilizer may not release enough of their principal nutrient when the plant needs it for growth.

Cottonseed meal is a by-product of cotton manufacturing. As a fertilizer, it produces a somewhat acidic reaction; consequently, it is frequently used for fertilizing acid-loving plants such as azaleas, camellias, and rhododendrons. Formulas vary slightly, but generally, cottonseed meal contains 7 percent nitrogen, 3 percent phosphorus, and 2 percent potash. Nutrients are most readily available to plants in warm soils, but there is little danger of burn.

Blood meal is dried, powdered blood collected from cattle slaughterhouses. It is a rich source of nitrogen, so rich, in fact, that it may burn plants if used in excess. Gardeners must be careful not to exceed the recommended amount suggested on the label. In addition to nitrogen, blood meal supplies some essential trace elements, including iron.

Fish emulsion, a balanced, organic fertilizer, is a partially decomposed blend of finely pulverized fish. A strong odor is associated with most brands of fish emulsion fertilizer, but the smell dissipates within a day or two. Recently, deodorized brands have been developed.

Fish emulsion is high in nitrogen and is a source of several trace elements. Contrary to popular belief, too strong a solution can burn plants, particularly those growing in containers. In the late spring, when garden plants have sprouted, an application of fish emulsion followed by a deep watering will boost the plants’ early growth spurt.

Manure is a complete fertilizer, but low in the amount of nutrients it supplies. Manures vary in nutrient content according to the animal source and what the animal has been eating. A fertilizer ratio of 1-1-1 is typical. Commonly available manures include horse, cow, pig, chicken and sheep.

The highest nutritional concentration is found in manure when it is fresh. As it is aged, exposed to weather, or composted, nutrient content is reduced. However, most gardeners prefer to use composted forms of manure to ensure lesser amounts of salts, thereby reducing the chance of burning plant roots. Because of its low concentration of plant nutrients, manure is best used as a soil conditioner instead of a fertilizer. Typical rates of manure applications vary from a moderate 70 pounds per 1000 square feet to as much as one ton per 1000 square feet.

Sewer sludge is a recycled product of municipal sewage treatment plants. Two forms are commonly available: activated and composted. Activated sludge has higher concentrations of nutrients (approximately 6-3-0) than composted sludge. It is usually sold in a dry, granular form for use as a general purpose, longlasting, nonburning fertilizer. Composted sludge is used primarily as a soil amendment and has a lower nutrient content (approximately 1-2-0).

There is some question about the long term effects of using sewage sludge products in the garden, particularly around edible crops. Heavy metals such as cadmium, sometimes present in the sludge, may build up in the soil. Possible negative effects vary with the origin of the sludge and with the characteristics of the soil where it is used.

Compared to synthetic fertilizer formulations,organic fertilizers contain relatively low concentrations of actual nutrients, but they perform important functions which the synthetic formulations do not. They increase the organic content and consequently the water-holding capacity of the soil. They improve the physical structure of the soil which allows more air to get to plant roots. Where organic sources are used for fertilizer, bacterial and fungal activity increases in the soil. Mycorrhizal fungi which make other nutrients more available to plants thrive in soil where the organic matter content is high. Organically derived plant nutrients are slow to leach from the soil making them less likely to contribute to water pollution than synthetic fertilizers.

(Excerpted from The Virginia Gardener Handbook, Diane Relf, Editor.)

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