Gardening: Time to fertilize your shrubs, trees and lawns

Eileen Ward
Be sure to read the directions and account for the exact type and amount of fertilizer that's best for your yard.

It is time to think about fertilizing your shrubs, trees and lawns. Our sandy soil allows nutrients to readily leach from the soil, so it is important to replenish these nutrients with fertilizer. You want to apply fertilizer while it is still warm, as the plants won’t take in the nutrients if they become dormant with the cold weather.

It will be important for your plants to be strong and healthy going into the cold months of winter. Healthy plants will withstand stresses from cold weather better than underfed, unhealthy plants.

What do those numbers on the bag’s label mean?

A 16-2-8 analysis on a 100 lb. bag means it contains 16 lbs. of nitrogen, 2 lbs. of available phosphoric acid, and 8 lbs. of soluble potash. The first three numbers are the primary nutrients. The first number is always nitrogen, the second phosphorus, the third is potassium. In addition to these three primary nutrients any secondary nutrients, or micro-nutrients, are listed at the bottom of the label in a similar manner.

For lawns a 16-0-8 or a 15-0-15 analysis would both be a good choice. Turf needs more nitrogen than do woody plants for turf density. This allows it to fight off weed invasions, tolerate foot traffic, and resist attacks from insects and diseases. On the other hand, too, much nitrogen can cause insect and disease problems. When the plant takes up too much nitrogen, its cell walls become thin, which makes it easier for fungi to invade. This will cause a higher than normal water need. This lush growth also attracts insects. The higher potassium content in the 15-0-15 fertilizer also helps with plant vigor, disease resistance and contributes to cold hardiness which is why I prefer it for the fall fertilization even though it is a little more expensive.

The state is demanding lower phosphorus rates in our fertilizers. This means the second number will be non-existent or lower than you were used to buying.

Turf will have a higher quality using a slowly soluble or “controlled release” material. While these fertilizers are more expensive your lawn will be healthier if you use them.

Look for the following when purchasing your lawn fertilizer.

  • Sulfur coated urea: Nitrogen release occurs as water moves through tiny cracks and pinholes in the sulfur coating.
  • Polymer coated urea: Urea granules with a polymer coating. Water diffuses through the coating to dissolve urea. Nitrogen release is affected by temperature and is more rapid in summer.

Sulfur and polymer coated urea: Polymer coating is added to the sulfur coated urea as protection and to slow the movement of water into the core. It combines the cost advantage of sulfur coated urea and improved release of polymer coated urea.

Palms under three feet use a light application of 8-2-12 monthly for maximum growth. For palms over three feet four times a year in early spring, late spring, summer and early fall using a palm fertilizer at the rate of 1 lb. per foot of trunk. It is best to use the special 8-2-12 blend recommended by the University of Florida. This blend has slow release nitrogen, potassium and magnesium (large white Kieserite). The boron should also be a granular slow release and the manganese and iron water soluble.

For shrubs, vines and hedges a good quality 8-2-8 analysis is recommended at a rate of 1 ½ lbs. per 100 sq. ft. Palm fertilizer is an excellent choice for all your acid-loving plants.

Four applications, in early spring, late spring, summer and early fall is what the literature recommends.

Bougainvillea prefers only once a year fertilization with 6-2-6 or 8-2-8 at a rate of 1/4 lb. per foot of height of bushy plant.

Citrus should be fertilized at a rate of ½ lb. of 8-2-8 every six weeks for the first three years. Wait until new growth begins after planting before fertilizing. After three years apply 1 lb. per year of age of the tree with each application of citrus fertilizer in January, June and October. Reduce to ½ lb. per year of age after ten years old. Also, if you missed the January fertilization wait until your fruit has set to fertilize. If your citrus is in bloom it may cause the blooms to drop resulting in a reduced crop.

It is my experience that two fertilizations, one in early spring and another in early fall, using a quality, slow-release nitrogen with micro-nutrients will keep the plants healthy and growing vigorously. If you have a weak or sick plant fertilize at optimal rates for a year or so until the plant is healthy again.

Always keep in mind that limited fertilization is much better for the environment than excessive fertilization. The Gulf of Mexico is beginning to show the results of our excessive use of fertilizer. State and local governments are beginning to address the problem of over fertilizing by controlling the products available and educating the consumer.

Spray companies should be targeted and trained to offer Integrated Pest Management programs to replace the blanket spray programs now offered. With new state limits on fertilizer ingredients and education for all we can make great strides to stop the pollution flowing into our local estuaries, rivers and the Gulf of Mexico.

Marco Island passed a fertilizer ordinance which has more stringent restrictions than the state model, which is the best model and was written following the science of the University of Florida. I have been an outspoken critic of the Marco Island ordinance and have started seeing more reports of government officials recognizing that following the science is the better way to go.

Since adopting the ordinance our water quality has gotten worse not better. The fertilizer label which, of course, “Is the Law” tells you everything you need to know to properly fertilize. And if you are fertilizing for hire the person applying the fertilizer needs to have a license from the state in their pocket. Not the owner of their company but them personally.

I’m not keen on restricting when you can fertilize. It is common sense that you want to stay away from fertilizing when we are experiencing heavy rains as the fertilizer will only wash through or off the soil and into the groundwater. However, when people fertilize in the cold months of winter using the 50% slow release demanded by the ordinance, the fertilizer can also leach into the groundwater as the plants have become somewhat dormant and are not absorbing this food thus the nutrients flow, unused, through the soil and into the water table.

An exception to this is the use of quick release nitrogen fertilizers to green up lawns in the dead of winter cold when lawns can sometimes turn an unattractive yellow. Under this ordinance you would be allowed to apply the slow release fertilizer at a time it would not be used by the plants and not allowed to ever use the quick release fertilizer that would do some good for your lawn.

A healthy root system will do a lot to absorb and use nutrients and pollutants and thus keep these undesirable elements out of the water. Fertilizing needs to be timed with mother nature and the plant’s needs and there are a lot of good reasons to use it sparingly all year. New landscapes are a fine example. No offense, but I don’t think the fine art of fertilizing belongs in the hands of code enforcement employees. It belongs with the people who are trained and know about plants and their needs. A healthy well fed root system is the Earth’s best filtration system and defense against all pollutants leaching into the water.

So please remember. When it comes to fertilizer, moderation is best, and timing is everything! So, complete this necessary chore before the cold weather arrives so the plants can use it and it doesn’t end up in our waterways.

Eileen and Peter Ward have owned a landscape and lawn maintenance company for 35 years. Eileen can be reached at or 239-394-1413.

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