Friday, March 15, 2013

How To Find Garden Answers Online

From the garden e-mail bag, Pat of Somerset, CA asks:

"My 13 year old grandson is doing a science project for school which involves planting a pea seed in 7 - 8  little cups of dirt then using different combinations of fertilizers:    nitrogen, phosphorus, potash, iron, manganese, boron,  to see the effects on the growth of the pea seed. He needs to sterilize the soil first.  What is your recommendation on how to sterilize a shovel full of garden soil?"

There's a short answer, and a long answer. The long one first:

Pat, this is what I would tell my grandson:  
"Put down that video game controller, get off your butt and head to the computer! You're 13 years old, for Chrissake! You know how to use the Internet better than I do! If you need assistance in finding the best online answer, I can help you there."

Give a kid an answer, and he'll be satisfied for five minutes. Your grandchildren might even look up long enough from playing "Call of Duty 10: Invasion USA" to nod and smile at you. But teach a kid how to use the Internet correctly to find that answer, and that child now has a vital, lifetime skill. 

Which brings us to today's rant:
Pat, you actually have a good question. But don't ask me. Use a search engine.

How to search for the right garden answers online.

No matter which search engine you choose, here are some parameters when searching for garden info:

1. All gardening is local. Learn to rely on authoritative sources in your area. So, be specific in your search query. 

Get in the habit of using ".edu" as part of your online search. For instance, if you did an online search of the word, "Aphids", you might see what I'm seeing right now: a Wikipedia entry, an entry from a site entitled Also, there is an entry from the University of California Integrated Pest Management info on aphid control.   

(hint: choose the UC entry. they're unbiased, informative and backed by research, not opinion. And they're local!)
if you narrowed your search query to "Aphids on Roses", you would get more exact information, but from a wider variety of sources. Of the first five that popped up on my search, only one was University-based (Oregon State). The others were commercial sites with something to sell, as well as one of the most dangerous sites for gardeners to heed: I-Village's, where anyone can chime in with their opinion. Yes, you might get some good answers. Some though, might be backed only by personal experience with something grandma told them. Or, since their answers are not reviewed for accuracy, they might (gulp!) make a mistake, especially when offering advice on amounts of fertilizers, pesticides or whatever to use in the garden. And you never know the real source of the information: is it someone trying to sell something that you may not need? (And frankly, that could be happening at your local nursery, as well).
So what's a gardener to do?

2. When searching online for garden answers, include your local university in the search query.

Enter the search term, "Aphids on roses UC". That'll bring up University of California-supplied answers in the first four queries. Some other examples of other universities to include in your search, depending on your location, include Oregon State University (OSU), Washington State University (WSU), Texas A&M (TAMU), Purdue and Cornell. Choose the university or college in your locale with the strongest horticulture program.

I'm not saying that colleges are pristine beacons of the truth. After all, some large, petrochemical company may have donated a sizable amount to help pay for that research. But, many University horticulture sites offer not only unbiased, well-researched information; they also make their pest control recommendations starting with the least toxic alternatives. Mechanical, physical and cultural controls are usually mentioned before pesticides. And that's where you should begin, too.

To repeat: using .edu as part of your online search will yield better informed results. Usually.

3. Make sure the online information is up to date. 
While researching garden information online, I've come across rather dated university research, some posts going back to the 1960's.
 If given the option of choosing two different, seemingly reasonable, university-backed pieces of Internet advice on the same topic...choose the most recent one.

4. Make sure the information is aimed at the home gardener, not the farmer. 
A lot of Internet searches for pest and disease controls may take you to University-produced pages aimed at commercial agriculture. In many cases, the product recommendations will not be available for the backyard grower; nor are they usually necessary.

5. Finally, for California gardeners, bookmark this website: 

This is the Integrated Pest Management site for the University of California at Davis, an excellent resource that can answer most any question about plant problems that you might be facing in your yard.

And if I may be so bold, (as well as the Twitter, Facebook and YouTube Farmer Fred pages) ain't bad, either, for Northern California garden advice. The vast majority of advice there is gleaned from University of California research.


And now the (not-so) short answer to Pat's question of sterilizing garden soil: 180 degrees for 30 minutes.

Google (or Bing or Yahoo or whatever) the words "how to sterilize soil in the oven .edu".
 Sadly, the information from Colorado State was the only university-based answer on the first three search pages at Google. So, narrow down the results even further by adding "UC" (for University of California) to the search query. And the first listing is from the Tulare/Kings County Master Gardener program on how to control fungus gnats in houseplants  (yep, control them by sterilizing the soil). In California, Master Gardener publications are subject to review by the UC experts. So, if there is a mistake, it should be caught. Theoretically.

But since I am a garden geek, I really enjoyed the detailed reply in the Colorado State University entry, entitled: "Start Seeds and Transplants in Sterilized Soil" written by  Laura Pottorff, Colorado State University Cooperative Extension horticulturist and plant pathologist, in 2010.

She writes: "You can choose from four methods to sanitize soil at home.

Oven Method- Spread soil not more than four inches deep in non-plastic containers, such as seed flats, clay pots and glass or metal baking pans. Cover each container tightly with aluminum foil. Insert a meat or candy thermometer through the foil into the center of the soil. Set the oven between 180° and 200° F. Heat the soil to at least 180° F; keep at this temperature for 30 minutes. Do not allow the temperature to go above 200° F. High temperatures may produce plant toxins. After heating, cool, remove containers from the oven and leave aluminum foil in place until ready to use. The heated soil will give off an odor.

Microwave Oven Method-You also can sterilize soil in a microwave. Microwave soil for 90 seconds per kilogram (2.2 pounds) on full power. Don't use metal containers and aluminum foil when using a microwave. Two methods suggested by others are:

1.  Fill clean, quart-size plastic containers with very moist soil, perlite or cutting medium.  Check the rims of the containers to make sure there is no aluminum of any kind because some yogurt containers come with a foil seal.  Use clean plastic yogurt containers with lids on for sterilizing soil.   This is done using a  temperature probe inside a carousel-type microwave oven, heating to 200F and holding that temperature with the digital oven program for 20 minutes.   Poke a hole through the plastic lids with a nail for steam ventilation.  The temperature probe goes half way down into the soil through this hole in one of the containers.  In a large microwave, up to 7 quart containers can be sterilized at a time, making this a very efficient way to heat sterilize soil.  Allow to cool and tape over the hole in the lid to keep sterile until ready to use.

2.  Place approximately 2 pounds of moist soil in a polypropylene bag. Leave the top open and place in the center of a microwave oven. Treat for 2½ minutes on full power of about 650 watts. After treatment close the top of the bag and allow the soil to cool before removing.

Pressure Cooker Method- Pour several cups of water into the cooker. On a rack above the water, place shallow pans containing no more than four inches of soil. Level the soil, but do not pack it down. Cover each container with aluminum foil. Stack the containers to allow steam circulation. Close the lid, but leave the steam valve open somewhat until all the air is forced out and steam begins to escape. Then close the steam valve and heat at 10 pounds pressure for 15 minutes. Turn off the heat, allow the containers to cool and remove. Leave the aluminum foil in place until you use the soil.

Steam Sterilization Without Pressure- Pour about an inch of water into the sterilizing container. Follow the soil preparation procedures for the pressure cooker method. Place filled containers on a rack to keep them out of the water. Close the lid and bring the water to a boil. Open the lid just enough to prevent pressure build-up. When steam begins to escape, continue boiling for 30 minutes. Then turn off the heat and replace the lid. Remove soil when cool.

Many heavier soils and soils containing large amounts of organic matter may release toxic compounds when heated too long or at too high a temperature. These toxins can cause poor seed germination, plant growth abnormalities or plant death. The toxicity is caused by an accumulation of ammonium compounds, soluble organic compounds, minerals or salts that may occur during the heating process.

Use a simple test to determine if the treated soil is toxic. Plant a few lettuce or other seeds with a high germination rate in the treated soil. If the seed does not germinate, toxic compounds may be present. To check the validity of the test, plant the same seeds in untreated soil."

Other entries on the Google search page on this topic were from non-university, commercial (click on the ads! click on the ads!) sources such as,,, and

I'm not saying that they're information is right or wrong...but the university postings were subject to peer review first.  

Your guidance with good advice on how to find the correct online information can be a lesson that lasts a lifetime for your children or grandchildren. Besides, your thirteen year old grandson is probably already aware of cannibis culture. Have you seen what's growing behind your garage lately?


  1. Or you could just buy bagged potting soil. Isn't that usually sterile?

  2. I have a bulb type plant that grows in early spring and develops a short lived white flower that is not un-attractive. My problem is that the plant propagates relentlessly and spreads to area in out planters that they are not supposed to be in. We are in the process of cleaning out our planters and I would like to eradicate the bulbs, place weed block type fabric and bark over some of the planters and save and augment some of the existing plants including daffodils and irises. Is there anything I can do to kill the existing bulbs (very small white bulbs) so they do not come back?


    Dennis Barksdale

  3. The easiest solution would be to throw out the soil in those pots and start with a fresh potting mix. If the bulbs are also in the ground, sheet mulching may work.