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"If a person is looking for a `one size fits all' prescription for a garden but doesn't want to bother with a good soil test, the only thing my conscience would let me recommend is adding compost," says Steve Rioch. Remember, though, that nutrientpoor soil produces nutrient-poor compost, and if you try to enrich a plot with materials grown on that plot, you'll still end up with the same deficiencies. The moral, then, is if you want to know how to best improve your soil's fertility, get a good soil test. My experts suggest using organically minded soil testers. If, instead, you get a state extension test or use a hometesting kit, the recommendations will be for specific doses of chemical fertilizers.

You can use the information that follows to convert those recommendations to natural amendments, and that trick may work out just fine. But it does carry some risk—and for a surprising reason. While underestimating how much of a nutrient you need has obvious drawbacks, excessive applications of a supplement are more harmful. In fact, the imbalances they cause can take years to correct. (Even an expert like John Jeavons, for instance, no longer tests his own soil but gets it professionally analyzed.)

I was a bit surprised when I learned about the risk of "overdosing" a garden. I suppose I was a victim of the common mindset that if a little bit of something is good, more of it must surely be better. I remember the first time I used natural amendments. I started out with a light application of those fine powders, but that dusting didn't look as if I'd put on much of anything (especially since I was used to spading on gobs of compost). So I began spreading the supplements freely—and didn't realize how excessive I was being until after I emptied the bags and then checked their labels. I had covered a few hundred square feet with fertilizer that was meant for an area four times as large.

I have two last words of advice (boiled down from my hours of phone calls): The experts I talked with all agree that within one to five years of adding the proper amendments, a soil should have good nutrient balance. Still, they say, it's a good idea to retest every five years or so. And they all shouted unanimously, "Never stop adding compost!" When humus levels drop in the soil (because you fail to keep boosting organic content), beneficial microbes die of. And those little critters are vital for breaking matter down into nutrients that plants can use and for enhancing soil structure in general.

What's What Among Amendments Here's a get-acquainted tour of the common natural amendments. Please note that the application rates mentioned are the maximum amounts to apply in any given year—a complete soil analysis will provide your best application guidelines.

Nitrogen (N) Sources:
• Hoof and horn meal (14% N, 2% P, 0% K). This odorous amendment is just what it says, a slaughterhouse by-product of ground hooves and horns. It starts releasing in 4-6 weeks and lasts 12 months. Use up to 4 lb./100 sq. ft.

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