Green Thumbs Up...

...to choosing fertilizer by soil test

Can I use hollytone fertilizer on the lawn? Rose fertilizer on the vegetable garden? Acid loving evergreen food on clematis? Indoor plant food on my perennial seedlings? Yes, yes, yes and yes.

Green thumbs down to the gardening marketers whose strategies for increasing sales have so muddied the fertilizer solution. A fertilizer's purpose is to compensate for imbalances in the soil. Plants have some slight variations in nutrient preferences but their primary needs are the same and even the outlier species grow adequately in soil that provides the Big Three: N (nitrogen), P (phosphorus) and K (potassium). Plants need only miniscule amounts of other elements, which is why those minerals are referred to as trace elements or micronutrients. Soil provides all the micronutrients plants need in most cases.

Buy the prescribed fertilizer

To know which fertilizer is best for a crop the farmer and professional grower look at the nutrient analysis on their latest soil test. If the analysis says the soil is fine but for nitrogen, nitrogen is what they apply. A little low on nitrogen and potassium, they use a fertilizer that supplies those two. The grower requests additional analyses if he or she is growing in soilless mix like the peat-based and bark-based media in most annual cell packs, greenhouse starter vegetables and potted perennial flowers Those mixtures are desirable for their sterility - no soil-borne fungi or insects - and quick drainage. Yet since they are soilless they lack minerals to supply trace elements. That grower probably uses an N-P-K fertilizer plus tiny amounts of iron, boron, sulfur and other minerals known to be vital to a particular group of plants.

 

Soil test results for our garden tell us to add nitrogen in the standard amount, that the soil needs 0 phosphorus but it is quite low in potassium. The prescription is for 6 times as much potassium as nitrogen. A fertilizer with analysis 1 - 0 - 6 would be perfect. We will use blood meal for nitrogen and green potash for the potassium.

Soil test results for our garden tell us to add nitrogen in the standard amount, that the soil needs 0 phosphorus but it is quite low in potassium. The prescription is for 6 times as much potassium as nitrogen. A fertilizer with analysis 1 - 0 - 6 would be perfect. We will use blood meal for nitrogen and green potash for the potassium.

12-0-0 bloodmeal is 12% nitrogen. That means a 10 pound bag has 10 x 12% or 1.2 pounds of N, enough for 1,200 square feet of garden. Since we need 6x as much potash we will use 48 pounds of 0-0-15 potash because 48 x 15% = 7.2 lbs

12-0-0 bloodmeal is 12% nitrogen. That means a 10 pound bag has 10 x 12% or 1.2 pounds of N, enough for 1,200 square feet of garden. Since we need 6x as much potash we will use 48 pounds of 0-0-15 potash because 48 x 15% = 7.2 lbs

Soilless potting mixes are peat based, or made of bark. Without any real soil they offer no nutrients. Without standard N-P-K plus micronutrients plants live but they are not healthy.

Soilless potting mixes are peat based, or made of bark. Without any real soil they offer no nutrients. Without standard N-P-K plus micronutrients plants live but they are not healthy.

Plants do not need "food!"

So why does fertilizer packaging feature plant names: Azalea fertilizer, Mum Finisher, Vegetable Starter? Some are insultingly inaccurate: Tomato Food, Bloom Booster are two. They are an insult to anyone who learned about the food chain in grade school. Its basis is that plants create their own food, all of it. It is the reason all other life on Earth survives, that given water and sunlight a plant can break and remake molecules to produce sugars, starches, fats, oils, proteins.

As for blooming, don't we wish we knew what makes that happen! We don't, although we know some triggers such as changes in day length and plant age. No fertilizer can make a plant bloom.

Marketing ploy

Anything on a fertilizer package other than "Fertilizer" and a list of ingredients is pure marketing ploy. If we were to go back to school our thesis could be to examine and chart the duping of the garden world from the advent of specialty fertilizer labels to the present, and its impact on fertilizer manufacturers' profits and the world's water quality.

Do you know that since mankind learned how to remove nitrogen from the air in the 1930's - a discovery driven by weapons manufacturers' needs - the amount of nitrogen applied to farm fields and drained away into the water is 40 times higher? Mankind has converted more atmospheric nitrogen into water soluble nitrogen in 200 years than all the nitrogen fixing bacteria and lightning of all the eons before. The algae and bacteria that "bloom" in our lakes and river mouths have appreciated the addition but it is unlikely that anyone's petunias are growing 40 times better!

It looks greener after a thunder storm because it IS greener. Lightning passing through our nitrogen-rich atmosphere converts nitrogen to soluble forms that rain down instant green.

It looks greener after a thunder storm because it IS greener. Lightning passing through our nitrogen-rich atmosphere converts nitrogen to soluble forms that rain down instant green.

Save money - do the math

So if you want to grow better gardens rather than line the coffers of fertilizer manufacturers, do a soil test and buy a fertilizer that matches the prescription you receive with that analysis. Until you have a soil test result, use a basic, balanced fertilizer. That means one with relatively equal amounts of the three most important elements in plant growth - N, P, K - which are also and not coincidentally the three ingredients the law requires producers to list on the label.

A 5-5-5 fertilizer has 5% each N, P, K. Fertilizer labeled 4-5-3 is 4% N, 5% P and 3% K. A 20-0-0 has 20% N and no P or K. Some 5-5-5 fertilizers are labeled as Rose Fertilizer, others as Vegetable Garden Fertilizer but all are good for any green plant.

The soil test says - woo hoo! - all your soil needs is N!

The soil test says - woo hoo! - all your soil needs is N!

Donate that potassium to someone who needs it!

Donate that potassium to someone who needs it!

The 15% potassium we will use for our K-poor soil.

The 15% potassium we will use for our K-poor soil.

Micronutrients for the seedlings in soilless potting mix

What about acidifiers, micronutrients and wonder-ingredients? Try letting Nature take care of that this year while you watch for how your plants do with the basics. Look around you and see what grows there naturally - oaks, wildflowers, elms, whatever. Look up those species in plant encyclopedias and note which "require acid soil" or benefit from additions of calcium. Be sure to move the book out of the way as you look again at Nature's work to notice no one is out there spreading acidifiers or lime yet those plants have prospered for decades or centuries. Plants are a lot more adaptable than fertilizer manufacturers and bushels-per-acre agricultural textbooks cause us to believe.

Not willing to do just the basics? We'll give you a pass if you are growing in soilless mix. In that case, do use one of the blue powders that lists "trace elements" or "micronutrients." If you are growing plants that require acid soil and you know from a soil test that your soil is alkaline, then spread a handful of soil sulfur on the plant's root zone or use acid-reaction fertilizers and mulch such as coffee grounds and cocoa hulls.

 See also Soil Testing in What's Coming Up #34

Download it here, it's a classic!

Ask us, we help with math and save the $s!

If you have specific fertilizer questions, head over to our Forum to follow the discussion there about finding a prescription fertilizer. We hope you will also add to the discussion.

http://forum.gardenatoz.com/index.php?/topic/986-need-fertilizer-recommended-by-soil-test-report/?hl=%2Bsoil+%2Btest

Everyone can read the Garden A to Z Forum. Members can also post questions, photos and suggestions. It is free and simple to become a Member. Sorry we must require Membership, otherwise computer bots and hackers invade.