It really irks me when I see fertilizer advertisements that try to take advantage of gardeners. I feel a need to bust some of the myths that impressionable gardeners may be inclined to believe. Here we go.
MYTH ONE: A simple complete garden fertilizer contains nitrogen, phosphorus and potassium in a ratio reflected on the label by three numbers, such as 10-6-4 or 16-4-8. These numbers represent the percentage by weight of each of these nutrients contained in the fertilizer. Generally, the first number representing nitrogen is largest because it is required in greater quantities than the other two nutrients and because soils often lack adequate nitrogen for plant growth.
Some companies promote specialized fertilizers with higher levels of specific nutrients above what you would find in a simple complete garden fertilizer. Ones with higher levels of phosphorus (the second number in the ratio) are touted for promoting flowering and are sometimes referred to as “bloom boosters.” Similarly, fertilizers with higher levels of potassium (the third number) are extolled for growing “bigger and more plentiful” tomatoes and other vegetables.
Specialized fertilizers are only needed when the soil contains inadequate levels of a particular plant nutrient. Gardeners should avoid fertilizers that will raise any soil nutrient to levels over and above what is needed for healthy plant growth. These products will not promote greater flowering or bigger tomatoes if adequate levels of those nutrients are already present in the soil.
Using a specialized fertilizer is a “shot in the dark.” Your money is better spent having your soil tested to determine if any nutrients are at growth-limiting levels. Once you have the results back from the soil testing lab, you will have a better idea of what nutrients are or are not needed and be able to select a fertilizer that best fits your needs. Without a soil test, the value of expensive specialized fertilizers is a myth.
MYTH TWO: Despite “miracle” fertilizers containing vitamin B-1 (thiamine) being marketed for many years to unsuspecting gardeners, there is absolutely no evidence that B-1 decreases transplant shock or promotes root growth. While there are plenty of testimonials that these products perform miracles, repeated research studies have found no evidence that B-1 has any positive effect on plants.
Does this mean that the touted benefits of seaweed or kelp extracts applied to the leaves of plants is also a myth? Actually, research has shown that seaweed extracts do indeed enhance root development, stimulate mineral nutrient uptake from the soil, and improve soil microbial activity. It is also true that seaweed extracts can enhance the growth and yield of fruit and vegetable crops.
MYTH THREE: Lawn fertilizer companies continue to market “winterizing” fertilizers that are formulated with higher levels of potassium to decrease the potential of damage to the grass plants from severely cold winter temperatures. Research has not shown that these winterizing formulas provide any protection from winter damage to cool season turf grasses like those found in local lawns. In fact, one study shows that they may make lawns more vulnerable to damage from snow mold.
Now that you know the truth, I feel much better. I recommend that you have your soil tested before buying any fertilizer for your yard or garden. There are several regional labs that will test garden soil for you. Northwest Agricultural Consultants (509-783-7450) is located in Kennewick, Cascade Analytical (800-545-4206) in Yakima, and US Ag Analytical Service (509-547-3838) in Pasco. Give them a call to find out how to properly collect and submit a sample.
Marianne C. Ophardt is a retired horticulturist for Washington State University Benton County Extension.