Hillsborough Extension Garden Blog

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Fertilizing the Landscape August 26, 2010

Filed under: Uncategorized — Hillsborough County Residential Horticulture @ 8:11 pm
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Just like humans, plants need nutrients for overall health. Nutrients like nitrogen, phosphorus, potassium, calcium, zinc, magnesium, and iron can be provided to plants in many ways, not just out the bottom of a fertilizer spreader. Products like compost or even grass clippings can provide nutrients in small amounts, reducing the fertilizer needs of a lawn or landscape over time.

Obviously, plants grow in the wild without assistance from humans, so the real purpose of applying fertilizer to a landscape is to satisfy some human need – to see more flowers, to increase fruit production, or to enhance a plant’s appearance. While those are acceptable reasons, it is important to make sure that the application of fertilizer does not exceed the plants’ needs or capacity to utilize the nutrients provided.

As with anything in life, there are consequences to excessive behaviors. Over-fertilizing may cause problems for the growth, appearance, and health of the lawn and other plants. Additionally, excess fertilizer can leach through the sandy soils typical of most of the state, contaminating groundwater supplies. Use caution when fertilizing near water bodies by leaving a 10- to 20-foot buffer zone to the water’s edge where no fertilizer is applied. This will reduce unnecessary runoff of excess fertilizer and the potential for polluting the water body itself.

There’s a lot of confusion when it comes to choosing the right fertilizer and knowing when, how often, and how much to apply. The goal of this article is to address some of the most common questions related to fertilizing lawn and landscape plants.

Q.  What is a fertilizer analysis?

A.  A fertilizer analysis represents the percentage of the three major nutrients found in the bag of fertilizer – nitrogen (N), phosphorus (P2O5), and potassium (K2O). Since most of Florida’s soil is high in phosphorus, it is recommended that the middle number of the analysis be zero, or as low as possible. Adding excess phosphorus to the landscape may result in leaching and runoff.

Q.  What is a “slow or controlled-release fertilizer”?

A.  This type of fertilizer contains a plant nutrient (usually nitrogen (N)) in a form that makes it available to the plant for a longer period of time than a typical quick-release (water-soluble) product. Additionally, less of that nutrient leaches into the soil from rain or irrigation, reducing the chance of groundwater pollution.

Q.  Under what conditions should the landscape be fertilized?

A.  There is no simple answer to this question. If aesthetics are not an issue or plants are established or in the process of fruiting, then fertilization may not be required. However, if plants exhibit certain nutrient deficiencies, are newly planted, or if the homeowner desires more or faster growth, then fertilization may be justified.

Q.  Should fertilizer be added to the hole at the time of planting?

A.  Adding fertilizer at planting has never been associated with improved or reduced survival. Application of slow release fertilizer is not likely to hurt the plant, provided it is applied according to the directions on the product. However, adding soluble fertilizer to a newly installed plant could burn roots if too much is applied. A safer recommendation would be to till the soil at the planting site (and the area around it) with an organic compost or soil amendment before planting.

Q.  How much fertilizer should be applied to the lawn/landscape?

A.  Fertilizer is applied according to pounds of nitrogen per 1,000 square feet of bed or lawn area. The phosphorus content of the fertilizer should be 0 to 2% P2O5, and the ratio of nitrogen (N) to potassium (K2O) should be 1:1 or 2:1. Slow-release fertilizers should be applied at no more than 1 pound of actual nitrogen per 1,000 square feet per application. Water-soluble fertilizers should be applied at no more than ½ pound of actual nitrogen per 1,000 square feet per application.

The table below indicates the recommended amounts for established landscape plants, depending on the desired level of maintenance.

Table 1. Amounts of Nitrogen Fertilizer vs. the Level of Maintenance for Landscape Plants

Level of Maintenance Amount of Nitrogen Fertilizer
Basic 0 – 2 pounds N/1000 ft2/year
Moderate 2 – 4 pounds N/1000 ft2/year
High 4 – 6 pounds N/1000 ft2/year

Source: Trenholm, L.E.; Gilman, E.F.; Knox, G.W.; & Black, R.J. 2002. Fertilization and Irrigation Needs for Florida Lawns and Landscapes (ENH860). Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.

For lawn areas, the fertilization guidelines are determined by the type of grass as well as the desired maintenance level.

Table 2. Fertilization Guidelines for Established Turfgrass Lawns

Species/Location Nitrogen Recommendations (lbs/1000 ft2/yr)
Bahiagrass – North

Bahiagrass – Central

Bahiagrass – South

2 – 3

2 – 4

2 – 4

Bermudagrass – North

Bermudagrass – Central

Bermudagrass – South

3 – 5

4 – 6

5 – 7

Centipedegrass – North

Centipedegrass – Central

Centipedegrass – South

1 – 2

2 – 3

2 – 3

St. Augustinegrass – North

St. Augustinegrass – Central

St. Augustinegrass – South

2 – 4

2 – 5

4 – 6

Zoysiagrass – North

Zoysiagrass – Central

Zoysiagrass – South

3 – 5

3 – 6

4 – 6

Source: Trenholm, L.E.; Gilman, E.F.; Knox, G.W.; & Black, R.J. 2002. Fertilization and Irrigation Needs for Florida Lawns and Landscapes (ENH860). Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.

Q.  What is the best way to spread fertilizer?

A.  The ultimate goal is to broadcast the fertilizer uniformly over the desired areas of the landscape. A properly calibrated drop spreader is the best tool for lawn areas, but may not efficiently reach all areas of landscaped beds. Keep in mind that if tree and shrub fertilization zones overlap with lawn fertilization zones, those areas should be fertilized for one or the other of the plant types – not both. Remember to apply no more than about ¼ inch of water to properly get the fertilizer into the root zone.

Q. Can palms be fertilized the same way as other landscape plants?

A.  Palms have different nutritional requirements than other plants in the landscape. If the palms are the primary concern, landscaped areas within 30 feet of large established palms should be fertilized with a 4-1-6-2 Mg (N – P2O5 – K2O – Mg) ratio fertilizer. The nitrogen, potassium, and magnesium should have equal percentages of each nutrient in slow-release form. Once this 30-foot area around the palm is fertilized, do not apply a separate fertilizer to any lawn or landscape plants found there.

Fertilizer, when applied properly to the landscape, can provide much needed nutrients to improve the appearance, growth, flowering, and fruiting of plants. It is important for homeowners to understand the nutrient need of their lawns and landscape plants, as well as their desired level of maintenance.

For more information on proper fertilization in your area, contact your local county Extension office (http://solutionsforyourlife.com/map/), a part of the University of Florida’s Institute of Food and Agricultural Sciences (IFAS).

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