The Truth About Organic FertilizersOrganic Fertilizers
There’s lots of confusion nowadays about “chemical” versus “organic” fertilizers but really, they’re all chemicals, so the correct distinction is between organic and synthetic. Organic fertilizers break down slowly, so they last longer in the soil than synthetics and their effect isn’t an instant “greening up” effect. They also require much larger quantities than synthetics to yield the same amount of each nutrient, and they’re more expensive. It’s those quick and cheap qualities of synthetic fertilizers – plus large advertising budgets on their behalf – that account for their popularity. That popularity will diminish if current garden trends towards organics continue, as expected.
Professor Jeff Gillman wrote The Truth about Organic Gardening to help steer environmentally concerned gardeners through the minefield of misinformation about organics. He warns readers that some organic fertilizers – like rock phosphate – are mined from nonrenewable sources and do considerable damage to the land. (The same harmful effects result from the mining of potassium used in synthetic fertilizers.) Nonmined organic fertilizers include compost, bonemeal, blood meal, seaweed extracts, alfalfa meal, and fish emulsions.
A common criticism of the excessive use of fertilizers is that they leach into groundwater, but the notion that only synthetic fertilizers do this is wrong, says Gillman. If organic fertilizers are overapplied, they’re just as likely to pollute our waters as synthetic ones.
But probably the biggest misconception about fertilizers as a group is that they’re even necessary! Usually, it’s far better to just feed the soil so it’ll support healthy plants, and not just by providing the nitrogen, phosphorus, and potassium in most packaged fertilizers. Healthy soils also need organic matter, plus beneficial bacteria and fungi, and the best source of all of that is compost. For growing food, Gillman recommends mixing a half-inch of aged composted manure into the soils.
I asked Gillman about growing shrubs, trees, and perennials and his good-news answer was that they don’t even need compost! He simply gives his a yearly 2-inch layer of a good organic mulch, which has been my own practice for 30 years, with good results. (I use leafmold, which is chopped and aged leaves, supplied free of charge by my local public works department.) One small exception is that to maximize blooms on roses, many growers recommend applying an organic rose fertilizer like Rosetone in mid-April and again in mid-May, and Gillman himself applies alfalfa meal to his roses. The other exception among ornamental plants is container plants. They’re watered SO frequently, their nutrients leach right out the drain hole, and most are planted in sterile “soil-less media” anyway. For pots, Gillman recommends fertilizers based on fish seaweed.
But what about the primary recipient of over fertilizer in the garden – our lawns? Turfgrasses DO need nitrogen, so a yearly application of any prepared organic fertilizer or a half-inch of screened compost is recommended. Even better, though, is corn gluten. Applied at the right time (when the forsythia is blooming) corn gluten will prevent weeds in addition to providing all the nitrogen the lawn needs. What a deal!