• More Blogs
• Observations »
• Bering in Mind »
• Cross-check »
• Extinction Countdown »
• Solar at Home »
• Expeditions »
• Guest Blog »
• Anecdotes from the Archive »

Gardeners, take note: the secret to growing hearty tomatoes is remarkably close at hand. Look no further than your fireplace and, er, your bladder.

According to a study from a group of environmental scientists at the University of Kuopio in Finland, human urine and wood ash make a reasonably potent tomato fertilizer, boosting plant growth and fruit yield dramatically over untreated plants and nearly keeping pace with conventional fertilizer. The research appears in the August 26 Journal of Agricultural and Food Chemistry.

The idea did not come completely out of left field—urine and ash have individually found use in helping plants grow, and their beneficial aspects appear complementary on paper. A commonly used nitrogenous fertilizer called urea is prevalent in urine, and wood ash (the Finnish group used birch) is rich in nutrients, such as potassium and calcium, that urine lacks.

In the greenhouse test, urine alone actually produced more tomatoes than urine with ash did—and neither treatment produced quite as much as did the researchers' mineral fertilizer. But both urine-based fertilizers roughly quadrupled fruit production when compared to unfertilized control plants. The researchers estimate that the product of a single individual's micturition could fertilize 6,300 tomato plants a year, yielding more than two tons of fruit.

The addition of ash did confer some benefits—those plants were larger and grew fruit with significantly higher magnesium and potassium content. A panel of 20 taste testers rated all growing methods as equally tasty.

Some caveats, remain, of course. The urine in the Finnish study was stored in cool conditions for six months before use, and it is unclear what effects this had on its fertilizing properties. What is more, plants are often highly salt-averse, and it seems reasonable to think that the salinity of urine could be harmful at high enough doses.

Then there's the inevitable gross-out factor: The researchers caution that even though urine is usually free of the harmful microbes found in fecal matter, care should be taken to avoid direct contact between urine-based fertilizer and the plants themselves to prevent contamination.

Photograph of tomatoes (used for illustration only and likely not grown with urine-based fertilizer): ©iStockphoto/Funwithfood

10 Comments

1. 1. silvrhairdevil 04:35 PM 9/4/09

   "...equally tasty..."
   
   Hmmm

   Reply | Report Abuse | Link to this

2. 2. Nostrilbone 05:48 PM 9/4/09

   What a waste! If only I had known this, I would have started storing my urine as soon as I stopped wetting the bed. Give those Finns due credit. They're probably years ahead of the rest of the world in terms of urine storage. I bet they've got vats of the stuff!

   Reply | Report Abuse | Link to this

3. 3. scientific earthling 12:08 AM 9/5/09

   Caution: Don't use power station ash.
   In the Punjab the BBC reported power station ash treated in unlined pits contaminated the groundwater with uranium.

   Reply | Report Abuse | Link to this

4. 4. way2ec 12:48 AM 9/6/09

   Would this "homemade" mix work with other plants besides tomatoes?

   Reply | Report Abuse | Link to this

5. 5. Forlornehope 01:13 PM 9/6/09

   The farmer next door planted his fields with potatoes this year and all my tomatoes keeled over with blight - but next year - I can hardly wait!

   Reply | Report Abuse | Link to this

6. 6. windhorse 10:37 PM 9/6/09

   Many medications are excreted in the urine. You would be putting these medications in your soil. Many are already being found in our water supply.

   Reply | Report Abuse | Link to this

7. 7. way2ec 01:38 AM 9/7/09

   Good point windhorse. To make a bad joke, maybe by "recycling" my meds I could save some money.

   Reply | Report Abuse | Link to this

8. 8. Tom Storm 03:05 PM 9/7/09

   I live in Queensland Australia - and a 'bushy' friend of mine complained that I was using the 'dunny' too much (water is scarce here) and she suggested that I urinate in the garden...on trees...plants etc. Well I did - and began 'fertilizing' the lawn on a daily basis. However, after a couple of weeks the grass disappeared from my favored 'p' spot - subsequent research suggested I had over-fertilized with my daily streams and created a nitrogen burn hole in the lawn. Is this too much a a good thing - or should I add more water inorganically?
   
   Tom Storm

   Reply | Report Abuse | Link to this

9. 9. Plant Grow 02:22 PM 11/20/09

   This blog Is very informative , I am really pleased to post my comment on this blog . It helped me with ocean of knowledge so I really believe you will do much better in the future . Good job web master .
   
   <a href="http://www.hydroponicswholesale.com">plant growing</a>

   Reply | Report Abuse | Link to this

10. 10. Uncle B 07:55 AM 12/7/09

    Try pee pee on the cumbers too! Mine loved it! Squash too! I dilute 3 waters to 1 urine, and use as freshas possible, even houseplants benefit, and cheaper than the store bought stuff.

    Reply | Report Abuse | Link to this