In the wilderness, fallen leaves, dead plants, bird and animal waste are continuously recycled by the myriad inhabitants of the soil. This ongoing process maintains adequate nutrient content in the soil. It is useful to note that Mother Nature does not practice intensive agriculture.
In the early days of our nation some of the push westward was sparked by the exhaustion of the soils. Pioneers needed fresh land to farm in part because they did not know how to restore nutrients to the land they had wrested from the forests.
Step into any garden center today and you will find plenty of restorative resources. Now the question becomes: What do I need? The first thing that stands out on every label are three numbers. These stand for the proportion of the three most used soil nutrients, nitrogen, phosphorous and potassium (N-P-K). What do they do? Why, how often and how much do they need to be replenished? Furthermore, are any other nutrients needed in the mix?
Let's begin by taking a closer look at the Big Three. I promise that even though we are dealing with chemistry, we will not delve into the nuts and bolts of the processes. Our objective is to get a grip on the big picture so that we spend our fertilizer dollar wisely.
N is for nitrogen, the soil element most used by plants. It is essential to rapid growth. Nitrogen leaches from the soil with every episode of rain or irrigation, so the gardener must do something to replenish it. We need to add it every year to areas where annuals are grown. Perennials, shrubs and trees do not want a rich diet and are quite content with the nitrogen recycled into the soil by decaying organic mulches or compost.
P is for phosphorous, which is needed by plants to flower and fruit. This element does not move much in the soil; however, it can transform to become chemically unavailable to the plants. But beware of "super phos" products which some apply to have super blooming. Phosphorous can build up to toxic levels. Because it does not wash out of the soil, this is a difficult problem to solve.
K is for potassium which is second to nitrogen in the quantity used by plants. It is critical in sugar, starch and protein formation, among other things. Potassium both leaches from the soil and becomes fixated and unavailable to the plants.
Three more elements are needed in amounts that may warrant inclusion in your fertilizer. Let's look at these secondary nutrients.
Ca is for calcium, vital for cell growth, nitrogen use and root formation. Many old-time gardeners use an eggshell tea to add this nutrient. Calcium leaches from the soil and so must be replaced.
Mg is for magnesium, essential to the formation of chlorophyll, fats and sugars plants use. This is another one that washes out of the soil. Many folks go around with a bag of epsom salts to replenish the supply available to their plants.
S is for sulfur which imparts dark green color to leaves and stems. It is essential to the formation of vitamins and amino acids. Though it leaches from the soil, rain applies 10 to 20 pounds of sulfur per acre each year in this part of the world so there is no need to apply more.
A balanced slow-release fertilizer is generally the best way to go in the vegetable or flower garden. These have label numbers such as 10-10-10 or 12-12-12. The slow-release factor means they will last all season. Many of these products contain calcium and magnesium as well as traces of other elements. Read the label for the amount needed to fertilize your garden area. Apply at planting time because nitrogen begins to wash away immediately.
There are additional micro-nutrients which occur in such abundance and are needed in such small amounts that they rarely need replenishing.
As you can see from our chart, the pH of the soil is critical to all nutrients being available to plants. The optimum range is from 6.2 to 7.3. A pH meter is a terrific investment in trouble-shooting because if pH is the root of the problem, all the fertilizer in the county will not improve your plants' nutrition.
Master Gardener Ann Bartlett never lets lack of familiarity with a plant stop her from trying it in the ornamental beds around her home.