The mysteries of fertilizer uncovered

By Melanie Mathieson
Gardening Guru

The gardening season is well under way and most gardeners are pleased with their results so far. But what about fertilizing? Well fertilizing your garden is an important task that needs to be done, but it can be one of the most daunting and confusing tasks. This column will take the confusion out of what all of the numbers mean and how to choose a fertilizer to suit your specific needs.
Many gardeners have difficulty purchasing fertilizer for their lawns and gardens. What brand is best? What do all of these numbers mean? What type of fertilizer should you use on flowers, vegetables, lawn or trees?
Organic fertilizer is a fertilizer compound developed from decaying plant material. You may recognize organic fertilizer as the compost you make yourself or well rotted manure, for example. An inorganic fertilizer is derived from natural minerals or synthetic chemicals. Inorganic fertilizers come in many forms like powders, granular pellets, spikes and liquids. The type of fertilizer you choose should be based on its primary use and how it will be applied, not specifically the form or brand.
When choosing a fertilizer you will see three numbers on the package.
20 - 10 -10
N - P - K
What do these numbers mean? These numbers represent the percentage of the content of the amount of mineral corresponding to that number that is contained in the fertilizer. Even thought these numbers are percentages they will not add up to 100%, because of the other compounds in fertilizer. In all of the fertilizers on the market the numbers are always in the same order and always represent the same mineral.
Nitrogen - is always the first number. Nitrogen supplies plants with the nutrients and energy to produce green foliage. Nitrogen also supplies energy to the plant to produce stems, branches and stalks. Too much nitrogen will make a plant very green and leafy and will prevent flowers, fruit or seeds from forming on these plants. Too much nitrogen can also burn a plant and kill it. You use a fertilizer with a high first number in the spring on your lawn to promote a very green lawn. Evergreen trees also require larger amounts of nitrogen that other plants in order to keep their ever-bearing green foliage green throughout the seasons.
Phosphorus - is always the second number. Phosphorus is a nutrient that is essential to strong root growth and for establishing newly planted plants. A fertilizer with a high middle number (10-30-10) can be often marketed as a transplant fertilizer. You should purchase this type of fertilizer if you are growing your own seedlings for your flower or vegetable gardens or for when you are planting a lot of new plants in your garden. Apply this fertilizer to your seedlings with regular watering to promote strong roots and when you transplant new plants into your gardens.
Potassium - is always the third number. When you are growing fruits, vegetable and flowers, you want to purchase a fertilizer with a high third number. When fertilizing your vegetable or flower garden you would purchase a fertilizer with a high last number. You would also use the same fertilizer for your container gardens. This is the most common type of fertilizer used by vegetable and flower gardeners.
Note: that the fertilizer you purchase will have a percentage of all three numbers in it as plants need all of these nutrients. You will pick a fertilizer with the highest number of the three being the number corresponding to the nutrients you need most, as listed above.
Now it time to purchase some fertilizer - What kind do you buy? Fertilizer comes in many forms. You need to decide what you need a fertilizer for. For lawns and large areas fertilizer comes in a granular form. Some of these granular forms can be immediate release or slow release. Immediate release means that the fertilizer will dissolve in a few days and supply nutrients to your plants. Slow release dissolves over a longer period of time allowing small amounts of nutrients into the soil over a longer period of time. I prefer to use slow release fertilizers for a couple of reasons. You may only have to apply the granules once during the growing season, as many will last three months, also due to the slow release properties of the granules the process of over fertilizing is often prevented. You will not use the same fertilizer on your lawn as you would your vegetable garden. Your lawn requires a large first number (nitrogen) in the spring and may even contain some weed killing herbicide, so this fertilizer is strictly for your lawn. If you have large gardens to fertilize you would buy a granular fertilizer with a large last number (potassium) to ensure large fruits, seeds and blooms and sprinkle it over the soil. If you have a smaller area to fertilize in your garden, you may want to choose a powder to mix with water and you would fertilize when you water. The brand of this type of fertilizer is not important. You should read all of the labels of the brands available to you in the store specific to your needs ( for example: transplanting -high middle number or gardens -high last number). What you need to look for in a quality fertilizer is the coverage rate. A good fertilizer to choose regardless of name brand is one that uses less product to more water. This means that the fertilizer contains more nutrients and less filler. The container of fertilizer will last longer, as a fertilizer that you mix small amounts of powder with large amounts of water is the best buy. When purchasing granular fertilizer you want to look for coverage per bag. The more expensive brands tend to have more coverage for the same weight of another brand. Compare the coverage on the back of the bag and be very careful, as a coverage of 400 sq. ft can easily look like a coverage of 400 sq. metres. The cheaper brand may only cover 400 sq. ft, which is only a space of 20 ft by 20 ft, and you will need many bags to do your yard. The more expensive brand will cover a place in your yard 1200 ft. by 1200 ft. (400 sq. m) therefore only one bag would do more than your yard. Some companies market fertilizers by certain names such as bulb, transplant, rose food etc. These fertilizers can be used on other plants as well as long as the numbers correspond to your usage for example bulb food has a high middle number ( phosphorus) so it is okay to use it for transplanting other plants as well.
Remember the easy rules for fertilizing and you cannot go wrong.
1. Never, ever add more fertilizer than the directions say. Too much fertilizer will kill your plants not make them better. Always follow the directions exactly and apply fertilizer following the schedule on the package.
2. Choose a fertilizer specific to your needs, with the right percentages of nutrients for your specific use. Buy the brands that give you the most coverage using the least amount of product
3. When in doubt ask questions (your local nursery can help you) and always read the labels.
I hope that this article has helped to clear up the confusion surrounding fertilizer.