Sciency Answers: The great fertilizer debate

Gary has a question:

Are organic fertilizers such as GardenTone and HollyTone really worthwhile using or is putting compost on your garden beds just as good?

Feeding soil versus feeding plants

Compost provides two things when you put it in your garden. A small amount of fertilizer for plants to take up, and a huge amount of food for all the earthworms, bacteria, fungi, and such in the soil. The fertilizer component is released slowly over time as the compost is degraded by soil life and taken up by plants to use to build leaves and flowers. The soil eating the rest of it improves the texture and structure of the soil making it better at holding water, nutrients, and allowing plant roots to grow through it more easily, so the same amount of fertility is utilized much more effectively.

Fertilizers, on the other hand, just provide nutrients for the plants. Because they are not tied up in the complex structures of compost, they are released quickly in higher concentrations to the plant roots. There really isn't much of a difference between organic and synthetic fertilizers here. The compounds the plant roots actually take up are absolutely identical in either case, and, depended how they are formulated, both synthetic and organic fertilizers will be released fairly quickly in high concentrations. Since both lack the bulky organic matter of compost or mulch, neither are going to do anything to improve soil structure and health in the long term.

More isn't always better

Fertilizers need to be used with caution. I grew up in a rural area where most people's "lawns" were really periodically mowed meadows, never fertilized or watered, and full of as many flowers (what the lawn care companies call "weeds") as actual grass. But we got a new neighbor who had lived in the city, who wanted a green, all grass lawn. They bought a bunch of fertilizer, and dumped it on. Their grass turned a vivid shade of green almost over night. And after the next rain storm, so did the drainage ditch all down the street and a good portion of our stream with a mass of algae spurred into growth by the fertilizer bonanza. Because fertilizers are quite concentrated and release their nutrients quickly, it is easy to over do it. You can harm you plants, but long before you do, you'll harm the more delicate life in the soil, and pollute your local ground water and wetlands as all the extra fertilizer leaches out of your soil.

The bottom line

In my own garden, I rely almost exclusively on compost and mulch to provide fertility. I do use more concentrated fertilizers, but only rarely in my container plantings, and very rarely in new beds that haven't yet been beefed up with enough compost for hungry plants like vegetables. In my ornamental beds, I don't even use compost, just regular mulching, because keeping fertility relatively low there keeps my plants a bit smaller and more compact so I don't have to stake them. When I do buy fertilizer, I frankly don't see much difference between synthetic and organic, so I go with price and convenience, which leads me to a slow-release synthetic fertilizer.

Have a question? Get a sciency answer! E-mail me: engeizuki at gmail dot com

Sciency Answers: Wood chips and nitrogen

Nancy has a question:

Hi, Joseph!  Looking for a Sciency Answer.
I keep reading that you can't use wood chips as mulch in gardens as it robs the garden of nitrogen.  Is that so?  How does that work?  What can I do about it?  Just add more fertilizer?  Wood chips are such cheap and easy mulch.
Thanks,
Nancy

The all importance of nitrogen

Wood chip mulches, and other high carbon, low nitrogen mulches, can suck up some of the available nitrogen in your soil. This happens because mineral nitrogen is essentially not just for plants, but for all life. Nitrogen is a key ingredient in proteins, and are a fundamental part of how life on earth works. The genes in our DNA are simply blueprints for making proteins, proteins which go on to build our entire bodies. No nitrogen, no protein, and without protein, no life. Which applies to all the soil microorganisms that want to decompose your woodchip mulch. To build their bodies and make their cool wood-digesting enzymes, they require nitrogen, specifically, mineral nitrogen, the form they can use. But mineral nitrogen is often in short supply in the soil. Everything wants it, and yet it is very easily leached away by rain water, and in the right conditions, can be converted into nitrogen gas which simply floats away in the air (forming, indeed, 78% of the air we breath). Only a few organisms, most famously the rhyzobium which form symbiotic partnerships with the roots of legumes like beans, can convert the gaseous nitrogen back into the mineral form other organisms can use.
So nitrogen is a key building block of life, and often scarce.

Carbon = food

Carbon compounds, on the other hand, from sugars to starch to wood, are primarily food for soil life. When a leaf or branch falls to the ground, all sorts of bacteria and fungi quickly begin munching away on it, breaking down the carbon structure to release the energy in it to power their life. When you, the gardener, take a whole bunch of carbon, in the form of wood chip mulch, and put it on the soil, the microorganisms rejoice and start reproducing like crazy. "So much food!" they say, "Let's all have a million babies to eat it all up!" But remember, each of those little baby bacteria requires a bit of nitrogen to live. If there is a lot of nitrogen in the soil to match the amount of carbon food sources, the microrganism population skyrockets and rapidly gobble down the organic matter, releasing all sorts of nutrients and making a lovely rich soil in the process. It is this balance of nitrogen and carbon that people aim for in their compost piles to achieve extremely rapid decomposition.

 When nitrogen runs low

If, however, there is a shortage of nitrogen, and lots of carbon, the bacteria are limited. Without enough nitrogen, they can't reproduce to match the food supply, so any bit of loose nitrogen they find floating around gets quickly snatch up and used to make more bacterium and fungi babies. With microorganisms scavenging up any loose nitrogen they can find, it doesn't leave much for plants to use to build their proteins and chlorophyll. The nitrogen has been immobilized. It is still there, just microorganisms are busy using most of it. Over time, however, as the microorganisms finish eating up all the carbon, they run out of food, and begin to die, releasing the nitrogen in their bodies back into the soil where plants can take it up again, re-mobilizing the nitrogen.

The wood chip nitrogen sponge

So when you add a layer of high carbon, low nitrogen mulch like wood chips to your garden, they act like a sponge, soaking up some of the nitrogen from your soil, and then gradually released it again. If you already have a shortage of nitrogen in your soil, this can cause a shortage for your plants , but you can solve that by simply adding a high nitrogen fertilizer, whether it be synthetic or organic fertilizer like manure, to make up the difference. And actually, adding nitrogen with carbon is better than just putting down the nitrogen fertilizer by itself. If you add concentrated nitrogen along, it will be instantly highly available to your plants, but it will also quickly leach away into the ground water, away from your plants that need it, and polluting streams and wetlands, forcing you to keep fertilizing to keep your plants growing happily. Combine that nitrogen with a lot of carbon, like wood chips, however, will keep the nitrogen around, releasing it slowly and stably over time, keeping your plants happy and minimizing polluting run-off.

The bottom line

So yes, wood chips can soak up nitrogen, but that is actually kind of a good thing. And the reality is, the effect is pretty small, and you don't need to worry about it in most cases. In my vegetable beds, where I want my plants to grow very rapidly and lushly in a single season, I add a higher nitrogen layer of compost annually along with new layer of wood chip mulch to keep the nitrogen abundant. In my ornamental perennial and shrub beds, however, I pretty much just mulch with wood chips, only adding compost if the soil is particularly poor and plants aren't growing well. Most plants don't really need high fertility levels. Extra nitrogen will help they grow bigger and faster, but for many flowers, that actually just means they are more likely to fall over and require staking, and sometimes even produce more leaves at the expense of flowers. I give a few greedy flowers, like my lilies, a big dose of compost every year to really push them to decadent proportions, but other wise, wood chip mulch produces healthy, happy plants for me.

In short, say yes to wood chip mulch!

Have a question? Get a sciency answer! Just e-mail me: engeizuki at gmail dot com

Sciency Answers: Fertilizers: Organic, natural, conventional or... what?

Dave sent me a question -- asking about my thoughts on some specific natural fertilizers that had been recommended to him. So, today's sciency answer is a quick run down on different types of fertilizers.

There are tons of differents kinds of fertilizers -- conventional liquids and powders, and a seemingly endless array of different organic options.

The first thing to say is:
Your plants don't care.
A plant's roots absorb certain specific compounds from the soil. And the phosphorus they get from an organic fertilizer is identical in every respect to the phosphorus they get from a synthetic fertilizer.

Which isn't to say what you choose doesn't matter. How a fertilizer is produced has an environmental impact. Synthetic nitrogen fertilizer is produced by the Haver process, an effective but energy intensive method to convert the nitrogen gas in the atmosphere into forms of nitrogen plants can use. Phosphorus for conventional fertilizers are actually mined -- and minable phosphorous in the earth is a non-renewable resource, and at our current usage rates, we're predicted to run out in about 30 years (A nice article on the topic from Slate: http://www.slate.com/id/2258112/entry/2258053/). In contrast, organic fertilizers like compost or manure let us recycle the nutrients we have. Though it is worth mentioning that shipping some sort of special organic fertilizers from across the country isn't going to be exactly carbon neutral either. Like very thing else, local is the best here.

The other big difference between different sorts of fertilizer is how concentrated and how "fast acting" they are. Highly concentrated fertilizers, like the genetic bag of 20-20-20 synthetic fertilizer OR the highly purified equivalent organic fertilizer bags, usually break down quickly in the soil releasing lots of nutrients in a rapid burst. This gives a satisfyingly rapid response from your plants, but also makes it much more likely you'll over fertilizer, potentially harming beneficial soil biology, and much increasing the risk of polluting fertilizer run off into ground water and wet lands. Most less concentrated fertilizers, like compost, don't release nutrients right away. Rather, soil microbes have to further decompose the compost to actually break down the nutrients in it to the forms plants can uptake. The result is a much slower response from the plant, with fertility that stays more constant, and much less chances for overfertilizing and polluting run-off.

The final benefit of using things like compost as a source of fertility is that they provides food for a whole host of soil organisms, creating a healthier, richer soil that retains water better, promotes healthy root growth, and allows plants to better utilize the nutrients that are already there.

So, in short: Highly concentrated, fast-acting fertilizers (organic OR synthetic) can give you impressive, quick results, but don't do anything for your soil, and can easily lead to polluting run-off. Less concentrated, slow-release fertilizers, like compost, take time to show results, but produce healthier soils that can grow great plants consistently over time. So in general, I am skeptical of any special fertilizer. Organic or not, the basic chemicals of fertilizers are all the same, and anything that will show results over night is probably not great for your garden in the long term. In the end, the basic standards, just local compost and mulch, are the simpliest, easiest, and best.

Wednesday Links

By way of The Scientist Gardener, the NY Times had a great article on green washing -- by individuals. We're used to hearing corporations criticized for pretending to be green, but there is a wider trend of justifying excessive, and ecologically damaging, consumption in the name of being "green."

I admit I'm drawn to the next subject partly because it is sort of giggle inducing (in a sophmoric way), but it actually is an important thing to think about. So, I bring you the Garden Professors talking about urine as a fertilizer. Jeff emphasizes nitrogen, but this article from Slate focuses recapturing the nutrients in urine from the prospective of the potential future phosphorus shortage -- including a discussion of special urine separating toilets, which solve the whole "yes, but how do you do it PRACTICALLY" side of the matter.

I saw this link on Margaret Roach's blog and was very intrigued: Right here in Michigan, researchers are having a field day to distribute Japanese beetles! Show up and get your free baggy of the little vermin! Japanese beetles, that is, infected with Ovavesicula popilliae, a pathogen which it is hoped will suppress beetle populations to low levels once established, and won't infect any other organisms. I really want to go and get some, but... it is on a Wednesday morning, an hour from where I live. Who thought of that timing? I'd have to take the day off work to go! If it was on a weekend I would absolutely be there.

Mr. Subjunctive writes about plant theft and the odd fact that many people somehow feel it is okay to pocket cuttings and even whole plants without permission. My take -- not okay.

Diana of Gardening on the Edge has a cool post about a shrew apparently infected with toxoplasma -- which is one of my favorite pathogens. It is a little organism that changes the behavior of rodents in order to get into the stomach of cats -- the only place it can reproduce.