Fall fertilization and other facts, myths and misconceptions

Coming up with a title for a discourse on fertilizer to keep you from blowing it off and saying, “Not another fertilizer article,” required some ingenuity. And you are correct — a lot of stuff has been written about fertilizer, and some of it has actually been interesting.

I particularly like the articles by the pundits that try to convince us that “organic fertilizers” produce better plants than “chemical fertilizers.” Oh really? Has anyone bothered to ask the plants? I would venture the plants don’t understand the concept of nitrification and why they need to wait for the conversion of organics to available nitrogen. Nitrogen, as the primary nutrient required in the greatest quantities, is by and large usable by plants only in the nitrate form. Organic nitrogen is not nitrate nitrogen and requires the “nitrification” conversion process to become nitrate.

Phosphorus
How about this one: “Lots of phosphorus makes lots of flowers.” I was taught that one in college, but that was a long time ago. Let’s take a closer look. What does “lots of phosphorus” actually do?
• It stretches internodes, making plants leggy, and in many cases, undesirable for sale.
• It can tie up root uptake sites for several other nutrients, including nitrogen.
• It leaches readily and has become one of our major environmental pollutants.

Controlled-release fertilizer
If you think about plant nutrition, you soon realize that plants require many of the same nutrients we do. Their handicap is that they can’t move around and search for their food, especially when confined to a container, so they need to rely on us to ensure their food is there when they need it.
 
Until the advent of controlled-release fertilizer technology, commercial fertilization in nurseries relied upon multiple applications of either granular or liquid fertilizers, and fertilization of nursery stock in containers was a challenge. Greenhouses, on the other hand, were able to embrace the water-soluble fertilizer concept through the use of injectors, coupled with the ability to direct the liquid application to individual plants with minimum runoff.  As new technologies in controlled release have evolved, such as the ability to produce controlled-release calcium nitrate, greenhouses growers are recognizing the benefits of controlled release as part of their production programs.
 
The controlled-release fertilizer concept has been in existence for more than 40 years. Despite claims to the contrary, all of the products currently available have these characteristics in common:
• All encapsulate a water-soluble fertilizer with some form of polymer coating.
• All are activated by moisture and release of nutrients associated with temperature — higher temperatures result in faster release, lower temperatures slow it down.
 
The difference between the various controlled-release fertilizer brands is the polymer coating. The release of nutrients and predictability of performance is dependent upon the polymer used in the coating process.

Fall fertilization
That brings us to the topic of fall fertilization. This concept has been tossed around for years, and I have come to the conclusion there is no definitive answer. But after years of observation and discussion, I have come to the following conclusion: Plants that are starved for nutrition as they go into their winter dormancy period have a greater risk for winter injury than those who have a reserve of nutrients to carry them through. In addition, when spring arrives and plants start their natural growth cycle, those with some nutrient reserves react more quickly to make that all-important first flush, the key to the entire growing season.
 
I need to stress, however, that plants pumped up with excess nutrients are unable to slow down in the fall and take advantage of their natural rest period, and the first real cold snap can zap foliage and freeze active vascular systems. And although controlled-release fertilizers generally slow down as temperatures drop, there is no way to precisely predict when and if the weather in the fall will cool gradually enough to sufficiently slow the release of nutrients and allow the plants to rest. In addition, we frequently have a January thaw in many parts of the country, and the fertilizer reacts as though it were spring, causing salts to build up and causing plant injury.
 
Even though the preceding may seem contradictory, what it boils down to is common sense. I am an advocate of fall fertilization as long as it is done sparingly. An application of a six- or eight-month controlled-release fertilizer at ¼ to ½ the low recommended rate will, in most cases, carry plants safely through the winter and still allow them to utilize their reserves to flush in the spring. I realize this is a broad stroke of a very general recommendation, and there are exceptions. For example, one exception may be deciduous shrubs. Normally we prefer complete defoliation during the winter to minimize susceptibility to disease and give the plants new growth in the spring. Fall fertilization may extend their growing season sufficiently to have them go into the winter unprepared for the consequences.
 
To help ensure safety in fall fertilization, I strongly recommend monitoring salt levels with a conductivity meter. A simple pour-through technique coupled with the ability to irrigate if necessary will help prevent unforeseen problems.
 
As I alluded to in the beginning of this discourse, there are a myriad of opinions out there regarding fertilizer, some true and some not so true. And I am certain many who read this will disagree and continue their current practices. This is not necessarily a bad thing because I certainly don’t profess to know it all. One of the expressions my dad used a lot, and it holds true here, is, “To change a man against his will leaves him of the same opinion still.”