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Have you ever noticed how many fertilizer choices there are?
Not only can the selection be large at a single garden center, each store carries different products. Continue reading to discover the differences between the two main types of fertilizers, synthetic and organic, so that when October arrives you will be ready to fertilize.
Synthetic/inorganic fertilizers are most abundantly available in stores, which will hopefully change. These fertilizers are made of salts that will dissolve in water, making the nutrients immediately available for the plants to absorb. The salts in synthetic fertilizer, when applied at a rate of more than 2 pounds per 1,000 square feet, will kill the soil microbes.
The nutrients, unless they are made to be slow-release, will not stay in the soil for long periods of time since they are water-soluble.
When synthetic fertilizer is applied, it should be watered in with a quarter inch of water to carry the nutrients down to the roots so they can be absorbed. If too much water, or rain, is applied, it will carry the nutrients past the roots. Once that happens, the nutrients will be carried to the groundwater and then to either the Indian River Lagoon or the St. Johns River.
Another way to think of fertilizing your yard with synthetic fertilizer is that you are growing your yard hydroponically in the sand. This is just one reason why both the IRL and the St John River are impaired water bodies.
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In contrast, organic fertilizers are made from animals (i.e., manures, sludge, fish meal, feather meal, bat guano, etc.) or plants (i.e., corn gluten meal, alfalfa meal, kelp meal, cottonseed meal, soybean meal, etc.).
The nutrients in organic fertilizers typically become available to plants slowly because they must be broken down by soil microorganisms. One exception to that rule is blood meal, which is a quick-release source of nitrogen that should be applied sparingly and watered in lightly.
With organic fertilizers, the soil microbes also store the nutrients and water in their bodies. When a microbe is eaten by another (predatory) microbe or just dies, its nutrients and water become available to the plants, in small amounts.
Because of the slow-release properties of these materials, organic fertilizers are not prone to leaching through the soil, burning the roots of plants, or causing rapid growth spurts, which can attract insect pests like aphids.
This is important for both the Indian River Lagoon and the St. Johns River because the use of organic fertilizers can reduce groundwater contamination.
Many organic fertilizers also contain beneficial soil microbes, so they are a great way to inoculate your lawn, ornamental plants, trees, palms and edible plants with the soil food web.
The University of Florida discovered in 2006 that St. Augustinegrass has a symbiotic relationship with Glomus intraradices (now called Rhizophagus irregularis), which is an arbuscular mycorrhizae.
AM have relationships with up to 95% of plants. The exceptions to this rule are the Brassicas such as broccoli, cauliflower, cabbage and kale. These crops typically have a symbiotic relationship with bacteria instead of fungi.
St. Augustinegrass, which has established a relationship with Rhizophagus irregularis, will be able to grow much better because of the fungus’ ability to gather nutrients and water from a larger portion of the soil than the plant’s roots could ever do.
It is important to point out that fertilizing correctly begins with getting the soil tested.
A soil test will show if each nutrient is deficient or in excess. Excess nutrients can tie up other nutrients, making them unavailable to the plants, so applying more of an excess nutrient is a waste of money and will not help the plant.
It is important to know which nutrients need to be applied and how much. Our soil testing form can be found at edis.ifas.ufl.edu. Search for “soil test form.” Be sure to pay for the $10 Test B, which will measure the soil pH and levels of phosphorus, potassium, magnesium, copper, manganese and zinc.
The crop codes are on the second page, and if you are testing the soil around palms, use crop code 77, because St. Augustinegrass and palms have similar deficiencies.
Page 2 also explains how to collect a soil sample, where to send it, etc. The soil sample can be sent in a zip lock bag that has your name, address, sample ID, and crop code on it.
Organic fertilizers tend to be more expensive, so for a large yard that could certainly be an issue, but they will help to improve soil health and reduce the potential leaching of nitrogen or phosphorus into either the IRL or the St. Johns River.
Since the benefits of organic fertilizers are numerous, it may be useful to spend a little more upfront to inoculate the yard with the soil food web at the same time you are applying nutrients. For more information on that topic email me at firstname.lastname@example.org.
Once the soil food web gets established, you will have less work to do. After all, the establishment of the soil food web is the only way to turn dirt into living soil.
Sally Scalera is an urban horticulture agent and master gardener coordinator for the University of Florida’s Institute of Food and Agriculture Sciences. Email email@example.com.
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