Dear Science,
My tomato plants are struggling this summer. They are yellow and
weak despite good amounts of sun and water. Is there anything wrong
with using some Miracle-Gro? Would an organic fertilizer be
better?
Waiting For A Bloom
Sunlight, water, and carbon dioxide aren’t enough for your plant to
grow. Generating new DNA bases requires nitrogen; your yellowing
tomatoes need some. The atmosphere is about 70 percent nitrogen, but
the nitrogen in the air is quite chemically inert. Capturing and
connecting the otherwise content pairs of nitrogen to carbon or
oxygen—fixing the nitrogen—takes a bit of chemical
wrangling. Plants can’t do this for themselves. Some bacteria,
diazotrophs, can capture nitrogen, and the delightful legume family of
plants hosts these bacteria as symbionts.
Chemical fertilizers are generated with modern chemical engineering,
fixing nitrogen to carbon and oxygen with high temperatures and
pressures through the Haber process. From the perspective of most
plants, this fixed nitrogen is as usable and palatable as that made by
bean plants. Organic fertilizers, typically from sewage sludge or
animal manure, recycle some of the already-fixed nitrogen in the other
parts of the biosphere. Crop rotation—planting a round of
beans in your tired soil—also would do the trick.
Organic or chemical nitrogen fertilizers cause problems when they
are overused. The runoff of the extra nitrogen causes a bloom of wild
plants, disrupting the delicate balances of ecosystems. It isn’t
the source of the nitrogen—chemical engineering or
industrially processed manure—that matters, it’s how it’s
used.
You shouldn’t fear the chemical fertilizer over the organic.
Provided you use careful amounts of Miracle-Gro, your tomato plants
will be fine. The same is true of an organic fertilizer. The fact that
the chemical fertilizer comes from the other kind of plant isn’t, in
and of itself, a risk. Almost everything we eat or drink is
genetically modified and processed. From pigs to corn to wheat to
berries to broccoli—just about anything you’d find at an organic
farmers market is the product of millennia of selective breeding,
manipulation of the environment, and bending of the natural world.
Fearing science, and the application of scientific knowledge to the
problem of feeding humanity, is criminally
irrational—particularly in a world with nearly seven billion
people, many of whom are malnourished.
Overidealizing a romanticized notion of 19th-century
agriculture—dating back to a time before we even had the most
basic grasp of biology—goes beyond naive and into the absurd.
Feeding all of us properly is going to require us to apply
science to our food.
Next summer, plant some beans instead. The same advice applies to
industrial farms.
Reasonably Yours,
Science
Send your science questions to dearscience@thestranger.com
It is simplistic to compare selective breeding, which as you note has been part of humanity’s agricultural toolbox for millenia, with the type of genetic engineering that is going on nowadays. 19th century agricultural scientists didn’t have the ability to insert bits of fish DNA into tomatoes, for example. That’s not to say that we should be afraid, per se, of genetic engineering, but only that we are opening up a new realm of what it means for something to be identified as “food”.
Genetic engineering might introduce new allergic reactions to foods, for instance. Also, one aspect of GE that is criminal is for companies to introduce “terminator” genes into crops that have been traditionally saved and re-sewn the following season. These genes make the seed of the plants sterile and force poor farmers in the developing world to purchase new seed from large agro-corporations. Nothing is as black and white as we’d like to imagine it is, and many new technologies raise some new ethical and health considerations that we’d be wise to discuss without sugar-coating.
Also, are your tomato plants in a container or in the ground? If they are in a container then you can add fertilizer everytime you water and just collect the run off at the bottom. If they are in the ground you can use fetilizer more sparingly and at the same time throw some beans around them. Beans grow crazy fast.
Urine is a rich source of nitrogen, too. It’s readily available, and essentially free.
Hm…I don’t think beans will leave a net increase of N in the soil after the plant dies. The exception would be if you tilled them in before they fruited–like with vetches you plant as an over-winter cover-crop. But if they’re allowed to live out their lifecycle, they will put all that good N to their own uses.
That’s what Steve Solomon says in Gardening West of the Cascades…
Containerized tomatoes that turn yellow are frequently root-bound; they’ve run out of room to grow. You’d probably see roots running out of the holes in the pot if this were the case (if you don’t have holes in the pot, then they’re drowning).
Chemical fertilizers are faster-acting than organic fertilizers. If your goal is to get tomatoes fast, you should probably go chemical (although, frankly, I wouldn’t give any money to Scott’s, because I think applying chemicals to make your lawn green is stupid and harmful to the environment).
Whatever you do, don’t apply any liquid or chemical fertilizer (including urine) to the plant itself. They burn.
For next year, read Steve Solomon, and bury a slow=acting fertilizer under the plant when you transplant.
Go get you some fertilizer. I like a nice time release granulated mix. The first number is nitrogen. Get something in the 10-20 range.
Yeah science!
You might be over fertilizing or fertilizing with the wrong ratio of nitrogen:phosphorous. My mom’s tomatoes are totally fine in standard soil so maybe chill with the moiraclegrow for a couple of weeks and see if that helps….
As a scientist and a teacher, I take serious offense at the notion that the industrial agricultural system is a sustainable one, and that all science is ‘good’ science. For example, it may seem that genetically altered rice crops- those engineered to contain beta-carotene- would be a ‘good thing’ for poor countries, but these crops are more often than not controlled by corporations like Monsanto, who care little whether the crops are suited to local conditions, and will fail over the course of 3,5 or 10 years- and leave the local populace worse off than when they started. This may be a better definition of ‘criminaly irrational’
This reply is one of an uninformed journalist- someone who only has a surface grasp of the repercussions of our current methods of genetic manipulation of crops and the consequences, and I cringe that this column purports to call itself “science”, as if it spoke for the entire scientific community. Shame on you.