Is Synthetic Fertilizer Really So Bad?

Most of the gardeners I know, read, and talk to have a strong bias in favor of an organic approach to soil fertility. I share that bias. In almost all of my garden, all I do is add mulch with some compost here and there. (And I’m planning on cutting back on the compost after I got back the results of my soil test.) Most of my plants are native wildflowers, cultivars of same, and vigorous exotics that just don’t need fertilizers if grown in the right kind of soil.

Even flowers with a reputation for being “heavy feeders”, such as Clematis and Bleeding Heart (Dicentra spectabilis) do fine in my garden with just a few shovelfuls of compost.

My Jackman Clematis gets only compost and it’s pretty happy.

But I have a confession to make: I do use some synthetic fertilizer. I’ve used it for three things: container plantings, my vegetable garden, and my roses. The first two have a rational basis: constant watering makes nutrients wash out of containers, and vegetable plants really are heavy feeders. As for the roses: OK, I won’t do this again, but I had just planted my first rose bushes and I wanted SO BADLY for them to do well and the roses on the package looked so happy …

Anyhow, I feel a definite sense of guilt when purchasing synthetic fertilizer. At Home Depot I asked for a plain brown wrapper for my container of Osmocote. But is the guilt warranted?

As I mentioned in an earlier post, I just finished a course at the Chicago Botanic Garden on Soil Basics. Very worthwhile course, very much geared toward gardeners and not scientists (very easy on the chemistry, etc.). From the class and assigned as well as supplemental reading I drew the following conclusions:

  • Synthetic fertilizers are greatly overused in home landscapes, and as such they can do substantial environmental damage.
  • Organic fertilizers and soil conditioners improve soil structure, generally contain micronutrients at appropriate levels, and are much less likely to create excess concentrations of nutrients and cause nutrient runoff.
  • Synthetic fertilizers are not inherently bad. The degree of concentration and the extent to which a fertilizer is fast acting are more important than whether the fertilizer was created through an industrial process or through the decay of organic materials.

Some have argued that synthetic fertilizers should not be used at all because they damage or destroy the soil food web – the vast number of bacteria, fungi, and other critters of varying size that are essential to soil fertility. This position is laid out in Teaming with Microbes by Jeff Lowenfels and Wayne Lewis. I found that particular argument unconvincing, though otherwise I found this to be an excellent book.

Synthetic fertilizers usually make nitrogen available to plants in the form of nitrates, a kind of salt. “Fertilizers are salts,” say Lowenfels and Lewis, and these salts “suck the water” out of soil microbes, drive away worms, and cause the overall soil food web to decline.

One problem with this argument is that nitrate salts are also produced by bacteria and fungi breaking down organic matter. Moreover, Jeff Gillman over at The Garden Professors cites a peer reviewed study showing that synthetic fertilizer was actually more effective than aerated compost tea at growing microbial populations in soil samples (though it also found that compost was better at helping poor soils retain nitrogen).

So that is my semi-informed, amateur take on the issue. What about you? Are you organics-only when it comes to fertilizer, or do you use a mixed approach?

24 thoughts on “Is Synthetic Fertilizer Really So Bad?

  1. I use both, I have to admit. Although I have to also admit to being so lazy that I generally just skip it. If I fertilize, I only fertilize my roses, but even they only get that maybe once a year. I could be wrong, and my garden might look much better with more fertilizer, but I think the soil and the water will give most plants what they need, especially as the mulch breaks down over time. Good subject.

  2. Ordinarily, I don’t buy much fertilizer of any kind, relying mostly on my homemade compost and the adage “feed the soil and the soil will feed the plants”. When I think something needs a boost, I usually turn to fish emulsion. This year my new raised beds started with a lot of peat and store-bought compost. They are basically big containers, though, and I had not thought about how all the watering I did during the drought was possibly washing away nutrients. More mulch is called for, methinks. Thanks for a thoughtful post!

  3. We use bone meal and fish emulsion when warranted. Otherwise it is compost and cow manure. Sometimes we make our own with coffee grounds, bone meal and granite dust for our acid loving plants like azaleas. I think soil tests are very important and will instruct the gardener as to what type of fertilizer/nutrients are needed and you go from there. Heavy fertilizing organic or synthetic is not helpful to the overall environment.

  4. In the post I put up yesterday, I mentioned that I rarely use fertilizers, and when I do, they are organic ones. I used to buy potting soil that had fertilizer in it, but decided over the last couple of seasons to pay extra for the organic kind. I haven’t had any soil tests done, but might for the vegetable garden one of these days.

      • Some years are better than others in the vegetable garden. I forgot to mention that I do compost, and manage to get one application a season there. This year was very hot and most things did not do as well as usual. There were lots of tomatoes, but not many ripened before the freezes. I do have some ripening in the house, so am happy about that.

        One of the problems there is that there are more and more locust trees sprouting up form the neighbors’ tree that are probably taking nutrients away from the plants. Oh, but the garlic seems to do fine each year.

      • Here the tomatoes started really early, but by late August were having all kinds of problems. Have you tried making fried green tomatoes? On the locust seedlings – do you pull those up?

  5. I am the guilty one always armed with a jerrycan full of tomato feed. I compost and add that as well. Probably my plants have the horipticultural equivalent of very high cholesterol or whatever the plant overfeeding disease is. Interesting that composting alone can work because I would be happy just to do that.

    • Excess nutrients is usually more harmful to the environment than to plants (because of runoff). If the nutrients are highly concentrated enough, they can be toxic, that’s usually when the plant ‘burns’. You might find a soil test useful, but sounds like your garden is doing extremely well as it is.

  6. I use osmocote and miracle gro on my potted plants. Otherwise, it’s Tagro (our local biosolid fertilizer, home made compost, fish emulsion, and steer manure. Also, when I cut down plants in the garden, they usually get chopped up and thrown on the ground to compost in situ.

    • I also use osmocote on my containers, though not miracle gro. In the beds it’s just mulch and compost. I also let most of the plant stalks etc. lay on the garden – don’t chop it up that much, would love to get a shredder/chipper.

  7. I primarily use compost and vermicompost; also, a little liquid kelp. I am seriously lazy about fertilizing, however – beyond the compost I use in the fall and spring, my plants are lucky if they get one or two additional feedings during the growing season.

  8. I use organic fertilizer, especially fish emulsion, for all of my in ground plants. I also use an epsom salts solution once or twice a year for many of my plants, especially when they are heat stressed during the summer. I use Miracle Grow only for potted annuals.

  9. I have mushroom compost brought in once a year for March and use it for everything, even topdressing my containers and vegetable garden (which is actually a very large container full of compost!).

    There is the danger of burning your plants with too much nitrogen (no matter what you use), or over salting them with syn. fert…. but I think that the “environmental damage” caused by most home gardeners with syn. fertilizer is blown out of proportion. Where it is really damaging is on the large to gigantic farm level.

  10. Since I moved back to the farm, I do miss my oak leaves in Mississippi, but I have gained “THE GOOD STUFF”. The piles of decomposed manure where the cows were fed hay over the winter several years ago is just AWESOME!!!

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