As spring barrels down upon us, today we start a multi-part tutorial on supplemental fertilization. This is a longer-than-usual post, but so worthwhile. Honest.
Well, yes and no. And, from where I stand, mostly no. So first and foremost, get a soil test (kits available from your local Cooperative Extension agent). How you gonna know what to add if you don’t know what’s missing?
In my opinion, fertilizers head the list of most-abused gardening products. The two main problems:
1) most people never think about why they fertilize; and
2) the combined powers of habit and advertising.
|Who wouldn't buy Miracle-Gro|
on this guy's say-so?
- Do I want organic stuff or are inorganic formulations just as good?
- Is there anything else I need to consider or should I just take my headache home for a nice nap?
To demystify the topic of topical fertilization, I’m going to run through a brief, ridiculously basic overview of plant chemistry. (Don’t stop reading: “brief and basic” represents the sum-total of my knowledge on the subject. I promise it will be practically painless.)
For optimum health, growth, reproduction, and resistance to pests and diseases, plants require the presence of 16 essential elements.
1. three structural elements: carbon (C), hydrogen (H) and oxygen (O), obtained by the plant from air and water;
2. three primary elements: nitrogen (N), phosphorus (P) and potassium (K)—to vastly oversimplify, nitrogen produces lush, green foliage; phosphorus encourages blooming; and potassium aids in building strong healthy roots;
3. three secondary elements: magnesium (Mg), calcium (Ca) and sulfur (S); and
4. seven trace elements: iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), boron (B), molybdenum (Mo) and chlorine (Cl).
(There are also seven important-but-nonessential trace elements: sodium, cobalt, vanadium, nickel, selenium, aluminum and silicon, but they come under the rubric of too much information.)
Structural, primary and secondary elements are called macronutrients, because plants need relatively larger quantities of them. Trace elements, only needed in tiny amounts, are micronutrients.
Plants take in primary, secondary and trace elements from the soil. Just like in humans, a serious lack of any of these elements results in one or more deficiencies, adversely affecting health and appearance.
And then there are single-element formulations, such as blood meal (12-0-0), superphosphate (0-45-0) and greensand (0-0-.1). Some secondary and trace nutrients, such as garden lime and Ironite, are sold as single-element formulations too. These particular soil additives have N-P-Ks of 0-0-0 because there aren’t any primary elements in the bag. In our example, lime provides the secondary element calcium and Ironite (not surprisingly) gives you the trace element iron.
(click on the picture
to make it larger)
Okay. You’ve decoded your soil test and written down what the state says will be most beneficial for your shrubbery/flower beds/vegetable garden/lawn. (By the way, don’t waste a lot of time looking for the exact N-P-Ks the state recommends, because many of them don’t exist commercially. Soil tests are primarily a tool for farmers, who custom-blend their chemicals.) The next big thing to think about is whether you should buy a quick-release or timed-release product. Regular ol’ 10-10-10, for instance, is quick-release, meaning that the Ns, Ps and Ks get set loose all at once in the presence of water and/or high temperatures. Timed-release blends such as Osmocote keep their Ns, Ps and Ks in little sacs made of inert material that require the nutrients to osmose out over time, once the soil temperature reaches 70˚F.
What does it matter, fast or slow? When it comes to synthetic fertilizers, speedy delivery—damningly called nutrient dumping—increases the likelihood of your plants' foliage and/or root system suffering fertilizer-burn. Any time you mess with roots, you’re asking for trouble. Just like people, plants can process only so many nutrients at a time: unlike us, they can’t vomit or take Alka-Seltzer to relieve the effects of over-indulgence. Although more expensive by the pound (although not necessarily by available nutrients), timed-release blends are much better for the health of your plants.
As for Miracle-Gro and other water-soluble products, well, they don’t hurt anything (if you don’t count compromising the water table). The problem lies in how water goes through your soil. In sand, water drains away rapidly, so plants can only snatch at nutrients as they flow by on their way to the ocean. If your petunias and hollies are looking the other way at the time, they’re out of luck. In swamp-muck and other heavy soils, nutrient retention is higher, but I’d discourage liquid fertilizing until you’ve improved the soil to where it drains more freely, to decrease the likelihood of your darlings drowning. Water-soluble plant foods are fine for containerized plants, however; pots leach out water and nutrients quickly, so a shot every other week or so would be appreciated by their occupants. Besides, the “soil” in most containers is actually soil-less (read: “nothing alive in it”) anyway. As always, read and follow label directions.
That’s all I have to say about inorganic—a.k.a. “chemical” or “synthetic”—plant foods. (Literalists point out that everything is, at base, chemical. They’re right, of course, but they should lighten up.) Next time I’ll reveal what I really think about fertilizing vis-à-vis increasing sustainability in our gardens, and, by extension, on our planet.
Thanks for dropping by. Stay tuned.