Choosing the Right Fertilizer for Your Gardening Needs
Though most homeowners recognize the need to apply fertilizers to optimize plant growth there are many challenges when selecting the “right” kind of fertilizer for your lawn or garden. However, with a little pre-planning, the appropriate use of fertilizer in the right amounts at the right time can help supplement plants with needed nutrients that may be missing in your soil.
Do I need to fertilize?
There is a common misconception that plants should be fertilized on a regular basis; however, this is not the case. Regular application of mulched leaf and twig debris generally will provide all the supplemental nutrients that a plant will need. This is especially true when you are establishing new shrubs or trees, or have young plants. Mature trees, because of their extensive root system rarely require additional fertilizers. As long as a tree or shrub is flowering and/or fruiting regularly, there is no need to apply any additional fertilizer.
Additionally, unless you know the soil’s fertility you are more likely to apply too much or not enough fertilizer, which can stress plants, opening them to attack from plant diseases and pest insects. A soil report is the only accurate way to ensure you are delivering the right amount of nutrients to your plants.
What do those numbers on the bag mean?
Fertilizers are labeled with a guaranteed analysis of the three principle macronutrients: nitrogen, phosphorous, and potassium, or N-P-K. These numbers actually are a percentage weight of each nutrient in that particular bag. So, a 100 pound bag of 10-10-10 fertilizers will contain 10 pounds each of nitrogen, phosphorous, and potassium. A ‘complete’ fertilizer will have all three of these elements in the bag, while a ‘balanced’ fertilizer contains equal amounts of N-P-K. Applications should be made over a period of time, rather than all at once. Spreading applications out over time will ensure a greater efficacy of the product for your plants.
Types of fertilizers.
Fertilizers can be broken down into two basic categories: organic and chemical. Organic fertilizers are made from a living plant or animal source, while inorganic fertilizers are those that are synthetically manufactured. Inorganic fertilizers are mostly made up of nitrogen, phosphorous, and potassium in forms that are water soluble and are almost immediately available to plants. Organic fertilizers contain other micro and macronutrients that are not readily usable by plants. In other words, organic fertilizers break down at a much slower rate and so deliver nutrients to plants over a longer period of time. Organic fertilizers are usually more expensive than synthetic ones. However, organic fertilizers help build soil organic matter content and soil physical structure over time.
Whether organic or synthetic, fertilizers applied at the wrong time or high quantities contribute significantly to groundwater contamination. Always apply at the appropriate rate.
Types of organic fertilizers include cottonseed meal, bloodmeal, fish emulsion, and manure. Cottonseed meal, a by-product of cotton manufacturing, usually contains a
ratio of 7-3-2. Apply cottonseed meal to acid-loving plants like azalea and camellias. Blood meal is the dried, powdered blood collected from slaughterhouses. It is rich in nitrogen and iron, among other micronutrients. Fish emulsion is a well-balanced fertilizer made of pulverized fish and is good for flowering plants and vegetables. Be aware that a main drawback of fish emulsion is the powerful smell that accompanies it. The smell generally dissipates over a couple of days, but the neighbors may complain, especially on windy days. Other organic fertilizers include: grass clippings, bone meal, alfalfa hay, and feather meal. All vary in their nutrient composition and nutrient availability to plants.
Synthetic fertilizers. These fertilizers are the most water soluble and thereby are ready for quick uptake of plants. Some are slow release, which means that the product will be delivered to the plant over a period of time. Most of the time these fertilizers will contain ammonium nitrate, ammonium sulfate, and urea, and provide quick green up. There are many synthetic fertilizers commercially available, and some are considered ‘special purpose’ such as those labeled as “Azalea food.” These products have an acidifying reaction and so are useful for acid-loving plants in alkaline or neutral soils.
For more information on fertilizers, contact your local office or visit http://ces.ncsu.edu, where you can post your questions via the ‘Ask an Expert’ link, or call 253-2610.
More information on fertilizers from Clemson University here.
Trees and Shrub fertilizers here.
Vegetable fertilizers here.