You might remember a nursery rhyme from your childhood that began, "Mary, Mary, quite contrary, how does your garden grow?" If you're hoping for healthy, thriving plants, you might want to ignore Mary's answer: "With silver bells and cockle shells and pretty maids all in a row" in favor of something more practical: fertilizer.
There seems to be some confusion about fertilizer among some readers who have sent me e-mail at steve@landsteward.org so this seemed to be a good time to take a look at some basic information about the subject.
I decided to turn to some experts for most of the information in this article and I always recommend that you do the same. One of the best sources of information will be the agricultural extension of a University in your area. The ag experts there have very specific knowledge about any unique peculiarities in your area and, in my experience, are very willing to help everyone from big farmers to small landowners.
First, let's take a quick look at those letters and numbers you find on the fertilizer bags. You'll notice the letters N (nitrogen), P (phosphorus) and K (potassium). If you want to know more about this subject (for example, the "K" refers to the chemical number K20 for potash) you can find numerous articles on soil and fertilizers at http://ag.arizona.edu/extension/
Now the numbers. A one hundred pound bag of fertilizer with the numbers 10-10-10 would indicate that it contained ten pounds of N, ten pounds of P205 and ten pounds of K20. Yes, that adds up to thirty percent. So what's the other seventy percent? Filler! Before you feel cheated, the filler serves an essential role, allowing you to spread the fertilizer evenly with less risk of "burning" the plants.
You might also notice the letters W.I.N. or W.S.N. on the label. These mean "Water Insoluble Nitrogen" and "Water Soluble Nitrogen". Simply put, W.I.N. is generally considered to be a slow-release source of nitrogen. As you might guess, W.S.N. dissolves much more readily. If you're not sure which will be best for you needs, ask at your garden center or contact your local agricultural extension. If you're still puzzled, I might be able to point you in the right direction if you contact me by e-mail.
There are three stages of growth for landscape trees and shrubs, according to the extension service of the University of Minnesota: the newly planted stage, the young rapid growth stage, and the mature maintenance stage. At each stage, they have different Nitrogen needs and the balance of the fertilizer you use should be adjusted accordingly. You'll find a much more comprehensive description here: http://www.extension.umn.edu/distribution/horticulture/DG7410.html or you can click on a direct link from my website, www.landsteward.org by going to "Plant Man" and finding this column.
Here is a brief summary. In growth stage one, transplanted trees and shrubs are liable to lose some roots. This is NOT a good time to use large amounts of quick-release nitrogen fertilizers as this can force canopy growth at the expense of root growth.
The second (or rapid) growth stage usually begins after about one full year in the soil. At this stage, the N rate should be 0.2 lbs to 0.4 lbs N/100 sq. ft. per year, applied in the spring and early summer, according the experts at the UMN Extension. If your trees and shrubs are on a lawn, consider reducing the N rate to 0.1 lb N/100 sq. ft. to avoid burning your grass.
During the third stage of growth you want to provide maintenance to mature trees and shrubs. As their growth rate slows, so does their need for nitrogen. In fact, lawn-based trees and shrubs might need no additional nitrogen at all, while elsewhere a rate of 0.4 lb N/100 sq. ft. every 4 to 5 years should be sufficient. Again, this is a general guide and specific needs on your land might vary somewhat, and the nitrogen requirements of fruit trees can be a little different, so get some local advice!
What about manure? It can certainly be described as "all natural", and if you happen to own a couple of horses or know someone with a few head of cattle, then manure has one major advantage: It's free. But according to John Lory and Ray Massey at the University of Missouri extension program, "manure has a value on a field only if it offsets the need to purchase other nutrients or soil amendments." They go on to say, "Manure has characteristics that may reduce its value relative to that of commercial chemical fertilizers." They point out that manure is also a less dependable source of nitrogen and is considered to be a source of weed seeds.
Now, they're mainly talking about fertilizing large areas, such as farmland, and some of the drawbacks of manure might not apply to your circumstances. So if you're using manure and you're happy with the results (and the price)... keep right on shoveling!
The Plant Man is here to help. Send your questions about trees, shrubs and landscaping to steve@landsteward.org or mail to: Steve Jones, "The Plant Man", P.O. Box 686, McMinnville, TN 37111. For resources and additional information, including archived columns, visit www.landsteward.org
