Thursday, February 24, 2011


            Meanwhile, back at the miles of shelving full of plant foods, how do you know if a product is organic? Why, it’ll say so, right on the label. How do you know if using the product constitutes a sustainable practice? That’s a little trickier. As Tim likes to point out, there’s nothing more organic than petroleum: it’s just dead plants aged under great pressure for eons.

Never assume “organic” on the label automatically means “good for you.” In addition to crude oil, poison ivy is also 100% organic. So are cyanide, and strychnine, and curare. In The Truth about Organic Gardening, author Jeff Gillman cautions that rotenone, a botanically derived insecticide (from South American derris root), is extremely toxic to beneficial insects, fish and humans. He believes that it would not be available, ironically, if it were not “organic.”

Espoma's Organic Traditions line
Tim and I espouse Espoma products. They are almost entirely sustainably derived and environmentally neutral, and readily available in our area. For mail-order, I like Gardens Alive! products. They use ’way too many exclamation points, but sell good stuff.

To reiterate, Tim and I feed our soil just before spring kicks in by mixing two cups of kelp meal into every 50-pound bag of Black Kow. The 2727 square feet of planted area on my 55-by-120-foot lot uses about 25 bags of Kow and kelp, or roughly about one 50-pound wheelbarrow load of Kow and kelp per 100 square feet. Tim occasionally topdresses the 2459 square feet of lawn (that shrinks a little every year as the resident plant-fanatic needs more space for her newest treasures) with eight to ten bags of sun-dried, unadulterated Kow.

Sandy soil needs all the nutrient help it can get. At your house, adjust amounts according to your soil-test results.

Length in feet times width in feet
equals square feet

(Don’t know how to figure square footage? Slept through that geometry class in tenth grade, eh? Just measure your beds as if they were all rectangular, and then multiply length by width. For example, the lovely uterus-shaped area in my front yard measures 1044 square feet when rectangle-ated, 36 feet times 29 feet. Ergo, this bed needs roughly ten 50-pound loads of Kow mixture.)

Let’s talk a little bit about everyone’s favorite soil additive, nitrogen. The following gets a bit technical: just read it slowly, going back over the parts that don’t sink right in, and you’ll be fine. We Americans need to get beyond our science-phobia.

The microorganisms in your dirt really matter, precisely because the amount of nitrogen available for plant use depends upon the total biomass of bacteria and fungi in the soil. This is how it works: a good chunk of the energy photosynthesis creates gets expended in the production of chemicals, which ooze out through the roots. These exudates, as they’re called, are sugars that attract and nourish beneficial bacteria and fungi. The microbes consume the exudates, thus fixing (immobilizing) nitrogen and other nutrients in their bodies, becoming in essence tiny, living bags of fertilizer. Enter the fertilizer-spreaders, the protozoa and nematodes. These guys eat the bacteria and fungi to power their own metabolisms. Whatever they don’t use is excreted (or “mineralized”—isn’t that a nice way to describe poop?) in a form plants can use. Without microscopic organisms exuding, eating and excreting, your soil becomes sterile. Most plants really struggle in sterile soil.

In fact, they die.

The nitrogen in protozoa poop comes out as ammonium (NH4—nitrogen bonded to hydrogen), but may be converted to nitrate (NO3—nitrogen bonded to oxygen) in the presence of bacteria.

So what? you ask grumpily.

So this. Pay attention: behavior-changing enlightenment follows. Research has demonstrated that, in general, perennials, shrubs and trees prefer their nitrogen to be hydrogenated, as ammonium. The ammonium excreted by protozoa stays in that form in a soil where fungi outnumber bacteria. If bacteria hold the upper hand, as in sandy soils, they oxygenate the nitrogen, converting it to nitrate. Annuals, grasses and vegetables (which are just annuals we eat) like their nitrogen as nitrate.

Read that paragraph again. It’s telling you something really important about your plants’ dining preferences.

Here’s the kicker: the nitrogen in most commercial fertilizers comes in the form of nitrate, favoring bacteria at the expense of the fungi. So while nitrate fertilizers are great annual-and-grasses pleasers, they’re not the first choice of your perennials, shrubs and trees.

Now it’s time for a little question-and-answer period.

Question: How do I know if my soil is full of fungus or brimming with bacteria?

Answer: Depends on the pH. Acidic soils favor fungi; bacteria prefer neutral to alkaline.

Q: I live on the coast. What kind of soil pH am I likely to have?

A: Neutral to alkaline.

Q: So that means my lawn, annual beds and vegetable patch will do okay without amending?

A: Well, I wouldn’t say without any amending. You still need composted materials to add organic material to sandy or swamp-mucky soil. And you should attend to any glaring deficiencies noted on your soil test.

Q: But I have a lot of shrubs and trees around my house, and I’ve been thinking of putting in a cutting garden. Short of moving inland, what environmentally responsible steps can I take to encourage more fungi in my soil?

A: Offer them food they like. Use organic mulches like shredded hardwoods, shredded leaves, or newspaper. The browner, the better. (What’s “brown”? See the “Compost Happens” posts.) Apply supplemental nitrogen only as ammonium—no sense making it easier for those nitrate-loving bacteria. Always study the label on any fertilizer you spread, even the organic ones.

Q: So what you’re really saying is that I want to feed my microbes, not my plants?

A: Bingo.

Thunderstorms bring atmospheric
nitrogen down to earth

If your dirt’s in pretty good shape, with healthy populations of microbes, protozoans and arthropods, it already has sufficient nitrogen in it. Earth’s most plentiful element, nitrogen accounts for 78%-by-volume of our atmosphere. Another significant bit of terrestrial nitrogen comes from lightning and rain-water. (That’s why grass looks so much greener after a thunderstorm.) Certain bacteria, either living free in the soil or colonizing the roots of leguminous plants, convert nitrogen in the atmosphere to a plant-friendly form. The damn stuff is everywhere.

And, yes, Virginia, you can have too much nitrogen. Besides root burning, overdoses cause lanky growth and favor foliage development at the expense of flowers. Wisteria, for instance, will bloom sparsely or not at all if you dose it with nitrogen. You’ll get leaves and shoot growth galore, but no flowers. And frankly, there’s no point in putting up with wisteria if you don’t get those gorgeous, fragrant, spring blooms.

Bulb-Tone has 2.4%
Water Insoluble Nitrogen

If you still feel compelled to apply nitrogen, spread it just before a rain or an irrigation cycle. Nitrogen moves easily into the root zone as long as enough water is present. When buying formulations with high N numbers, check the label for the WIN (water-insoluble nitrogen) percentage. In order to increase nitrogen uptake and decrease loss through volatilization, WIN should be at least half of total nitrogen. In the unlikely event your soil test comes back declaring a lack of nitrogen, use cottonseed meal (6-2-1) to remedy the situation. (Lowenfels and Lewis advise avoiding formulations that have more than ten percent of any of the primary nutrients, eliminating most commercial inorganic formulations with the ironic exception of the yucky 10-10-10.)

There! Now you’ve made your well-thought-out, sustainable decision about what to buy, paid for it and had the nice man load it in the trunk. Now are we done? Not quite yet. The little matter of where you ought to place your plant food needs some discussion, requiring a tiny bit of botanical knowledge.

But that’s for next time. Thanks for dropping by.


P.S.—For my new Winding River readers, here are some pictures of Lespedeza thunbergii ‘Pink Cascade.’ Nice plant, huh?