The Q&A Archives: Starting Seeds for School Experiment

Question: I am thirteen and have had my own garden since I was eight. I am planning to enter a science fair in mid-April, and I wanted to choose an experiment where I could really use the results. Since I love to grow zinnias, I thought I would test which additives improved the performance of zinnias in my 3 foot by 20 foot garden in the foothills of the Wasatch mountains. I wanted to use my own soil for this experiment if possible. It is sandy and somewhat alkaline, although I have added a lot of organic material over the past two years. However, your catalogue says "Never use garden soil for seedlings . . sterilizing your own soil is messy and difficult." Since my goal is to conduct an experiment, I was wondering if you thought it would be possibleto sterilize my soil well enough to use it, and what tips you might be able to give me. And if you think this experiment is possible, what zinnia seeds would you recommend that I order? My favorite is Scarlet Splendor, but I'll get something else if it would give me better and faster results. <br><br>Thanks so much for helping me get my project started!

Answer: Wow--you've had your own garden for five years? That's great! And I bet it's a beautiful garden! It's great that you have chosen an experiment that has real meaning for you. <br><br>First of all, you probably know that it's best to use a sterile medium for seed-starting, because there are microorganisms in garden soil that can harm tender young seedlings. (The general name for such diseases is "damping off".) <br><br>I'm wondering why you want to use garden soil for starting your seedlings. You will probably have better, and more consistent results, if you use a commercial soilless seed-starting mix, since it will already be sterile and very light and well-drained.<br><br>That said, you should be able to sterilize your soil adequately. And since it's a sandy soil with lots of organic matter, it should have adequate drainage. To sterilize soil, (according to the book "Park's Success with Seeds", the classic book of seed starting!) bake the soil in a shallowpan at a temperature of 180F for 30 minutes. Use a meat thermometer to make sure the temperature is right. Take note that this might create an unpleasant odor! That should sterilize your soil adequately for your experiment. Good luck!

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