The lone voice of horticultural reason

Fertilizer Frenzy Part III

6-16-1999 — This week we conclude our discussion of one of the most bewildering topics in gardening: fertilizers.
Plants eventually use up the nutrients in soil. We add fertilizer, then, in order to replenish these nutrients. I don’t use much fertilizer because I use a lot of compost in my garden, either as a top dressing or to fill in holes every time I move a plant. But to kick things off I lightly fertilize with a basic 10-10-10 or 5-10-5 (depending on what I find in my cupboard left over from last year) once in mid-May, and again in July.

Now the big question: granular or water-soluble? Remember, in gardening, easy is not always best. A soil scientist I rely on points out that water-soluble fertilizers have distinct disadvantages. If your soil drains well, as it should, much of the fertilizer can pass right through the root zone without being drawn in by the plant. If it rains soon after an application, just about all the fertilizer is lost. Plus, we’ve had a wet spring and summer-when would we have been able to fertilize, with a water-soluble product? I never like to add water to a wet garden; keep it up and plants will rot. And claims of “foliar feeding” made by the manufacturers are nonsense. Plants don’t absorb main nutrients through their leaves, they are processed through their roots.

Granular fertilizers do a better, more consistent job. I circled each plant with a bit of granular this spring, and roughed it into the soil with a hand hoe. I didn’t water it in, because the soil was drenched. I let the next rain take care of that. Every time it rains or I water a small amount of fertilizer is released. My plants are happy because the soil around them contains a consistent, average level of nutrients. Plants fertilized with water-soluble products are more like heroin addicts, anxiously waiting for their next brief, sharp blast, and perhaps a bit cranky between hits.

If your flowers still don’t bloom, or bloom poorly, or if your vegetables don’t reach proper size and/or have perplexing disease problems, your soil may be more out of whack that standard fertilizers can remedy. Time for a soil test.

It’s easy. Call the University of Minnesota Yard & Garden Line at 612-624-4771 and order a soil testing kit. Follow the directions that come with it. You make a soil sample and mail it back to the U along with $7, and shortly thereafter you will receive, on one elaborate page, the results of your test.

The results will be indecipherable. Tape the page to your bathroom mirror, and study it a few minutes each day, as if memorizing a speech. Slowly the meaning will become clear, until you reach the point one morning where you say, “I get it! I understand what to do!”

First thing you’ll decipher is your soil lacks organic matter. Problem soil always does. It will suggest your soil is low in nitrogen-soil low in organic matter always is. Next discern if you are lacking (or overloaded) in phosphorus and potassium, and if so, to what degree. Study the data on the page and soon its meaning, and corresponding recommendations, will become clear.

Finally, the test results will tell you your soil pH, which is usually where much of your problems lie. What exactly is soil pH? I’m sure I have no idea, and I’ve read books on the subject. I don’t even grasp pH as explained in shampoo commercials. The number seven on the scale is neutral, that much I know; anything above seven is alkaline, below seven is acidic. Best I can figure, pH relates to nutrient availability. Too high or too low and the nutrients in the soil (or supplied by fertilizer) don’t release. A soil pH between six and seven-mildly acidic-creates the greatest availability of nutrients. So that’s where you want your garden soil to be, in general.

Use soil sulfur to lower your soil’s pH (you can add bales of peat moss to a garden bed and not lower soil pH by more than .5) and lime to raise pH. Soil pH in our area tends to run neutral-to-alkaline to begin with; you’ll rarely find a situation where soil needs lime. I keep a crusty half-sack of the stuff kicking around in case I need to bury a cat, but that’s it. Yet I once came across a neighbor gleefully dashing lime across his lawn and flower beds, and when I asked him what he was doing, said, “I’m adding lime to everything, because it’s good for the soil.” No, it isn’t. Don’t use fertilizers and soil additives just for the sake of using them. There aren’t three gardens between here and Hudson that need lime.

Don Engebretson
The Renegade Gardener