Which Fertilizer is Best?

fertilizers

Slow release fertilizers are better for sandy soils. These include synthetic, time release products (left) and organic fertilizers (right).

There are lots of choices when it comes to fertilizing plants. Garden center shelves are lined with products that promise beautiful, healthy, lush plant growth. Some are added to the soil as a pellet or granule, while others are mixed with water and applied as a liquid. Which is best for your yard or garden depends on the type of nutrients your plants need and how quickly they need them.

WHAT DO YOUR PLANTS NEED?

Plants get the nutrients they need from the soil in which they grow. Many soils in southeastern North Carolina are naturally low in nutrients and require the addition of fertilizers to support healthy plant growth. This is especially true of deep, sandy soils.

The only way to know which nutrients are present in your soil and which need to be added is to submit soil samples to your local Extension office. Samples are analyzed by the NC Department of Agriculture’s soil testing lab in Raleigh at no direct cost to NC residents. Within a few weeks of submitting a sample your soil test report will be posted online. This will tell you which nutrients you need to apply and how much. It will also indicate if you need to add lime to your soil to raise the soil pH level. Many yards in southeastern NC have high soil pH, so never apply lime unless soil test results indicate it is needed.

The soil test report focuses on the three main nutrients plants need in the largest quantities: nitrogen, phosphorous, and potassium. Most fertilizers available today contain some of each of these nutrients. The percent of each of these nutrients contained in a fertilizer will be listed on the packaging as a three number analysis, with the numbers always in the order of nitrogen, phosphorous, and potassium. For example, a fertilizer with the analysis 10-5-15 contains ten percent nitrogen, five percent phosphorous, and fifteen percent potassium.

PROVIDING NITROGEN

Nitrogen is the most important and frequently needed of the three main nutrients. If your plants do not get enough nitrogen, they will stop growing and the older leaves will turn yellow and fall off. Most forms of nitrogen leach rapidly from the soil, meaning they dissolve in water and drain out of the soil as water moves deeper underground. For this reason, fertilizers containing slow release nitrogen work best for most plantings, especially in sandy soils.

Slow release fertilizers include synthetic time release fertilizers such as Osmocote, which have been coated so their nutrients release over an extended time, usually three to four months. Organic fertilizers are also slow release. In addition to feeding your plants, organic fertilizers build up levels of beneficial microorganisms in your soil, making soils healthier and improving plant growth. Brand names of organic fertilizer that are available at many garden centers include Plant-tone and Garden-tone.

Slow release or organic fertilizers should be applied to established landscape plants in spring and to annuals and vegetables at planting time. A second application is usually needed in late June for annuals, vegetable gardens, and plants in containers. Landscape plants growing in very sandy soils will also benefit from a second application in late June.

LIQUID FERTILIZERS AND COMPOST

The nutrients in liquid fertilizers such as MiracleGro or Peter’s Plant Food are immediately available to plants but do not last long. Liquid fertilizers are useful when plants need a quick boost of nutrients but slow release fertilizers are better for providing the nutrients plants need throughout the growing season. Watering newly planted flowers and vegetables with liquid fertilizers for the first few weeks after transplanting can help them establish since it takes slow releases fertilizers a week or two to start releasing nutrients. Organic liquid fertilizers include fish and seaweed emulsion as well as compost tea.

Old fashion synthetic granular fertilizers such as 10-10-10 or 8-8-8 act much like liquid fertilizers. Their nutrients, particularly the nitrogen component, dissolve rapidly. This makes them quickly available to plants, but also means they leach out of the soil quickly and must be reapplied during the growing season. Light applications made every four to six weeks are required to provide the same continued feeding slow release fertilizers provide with just one or two applications a season.

Soil amendments such as compost or aged cow manure provide some nutrients to soils but are not the same as fertilizers. Soil amendments add bulk organic matter to the soil, which improves moisture and nutrient retention, but are generally low in nutrients themselves. Mixing amendments into the soil before plantings will improve plant growth, though additional fertilizer is usually needed to supply enough of the nutrients plants need for healthy growth.

LEARN MORE!

Learn more about topics mentioned in this article from the following Pender Gardener articles:

Use Extension Search to find research based information from Cooperative Extension systems across the U.S.

Visit your local Cooperative Extension office to learn more about gardening and landscape care. Go to http://www.ces.ncsu.edu/local-county-center/ to find your county Extension center or post your questions to be answered online via Extension’s ‘Ask an Expert’ widget.

Contact your local Cooperative Extension office to get expert advice from an Extension Master Gardener Volunteer:


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Written By

Charlotte GlenExtension Agent, Agriculture - Horticulture (919) 542-8202 (Office) Chatham County, North Carolina

Posted on May 13, 2013

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