My landscaping science project part 1

Dino_Rabbit(10b)November 20, 2013

I am a ninth grader doing a science fair project. I decided to test some landscape coverings to see which ones blocked out the most weeds. I planted 16 weeds in each section and then put the landscape coverings over them to see which one would have the most weeds left over at the end. These are the results.
Control: 28 weeds
Clear Mulch (cut up gatorade bottles): 19 weeds
Rubber Mulch: 4
Pine Needles: 3
Black Mulch: 1
Granite Gravel: 0
Sand: 2
Weed Fabric: 2

I am a little confused on a couple of things.

What caused the black mulch to be so effective? It retains a lot of moisture, so would presume it steals some of the weeds' water, but it also keeps them cool.

Sand blocks out all sunlight, so why would there be any growth there? It is basically the same as gravel except for the particle size, so it should do much better than gravel. I think that some sunlight is maybe reflected off of the sand particles, but I am not sure.

I know that plants sense sunlight and grow towards it. Is this why the weeds in the weed fabric skirted around the fabric and came up out of the side?

Keep in mind that I planted 16 weeds in a 2x8 formation in a 11.5"x28" space. There were about 2" thickness of the materials, except for weed fabric (I put three layers of that). This was done in South Florida (Zone 10B).
Thank you!

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My guess on why the black mulch worked so well is the absorption of solar radiation= HEAT. Great that you are putting the scientific method to work!

    Bookmark   November 21, 2013 at 11:03AM
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You would need to repeat the experiment several times in order to truly know that the results are consistent. In horticulture, the climate which changes all the time, and seasonally, is a variable that takes a LOT of analysis. I'm not saying that repeating it is in your "scope of work," but it is part of how you would come to actually KNOW.

You can probably make guesses about the black mulch, but probably not know at this point. Why is the mulch black? Is it a chemical process? Are chemicals leaching into the test zone in minute quantities and having an effect? Does it create temperature differences? Does it pack tightly because of the particle shape and size? There is too much to question! And it suggests a need for further study in order to truly know the answers.

Sand ... while it blocks out all the light, plants have STORED ENERGY within them. Some seeds can grow several inches tall in pure blackness before they reach the soil surface.

In the summer, sand can get VERY HOT. In general, temperature usually plays a big part in how plants grow. I'd bet that the different mulches are all different temperatures so they may have different effects based on that.

Most weed fabric doesn't actually block light completely. Part of knowing depends on what kind of fabric you had. I'm guessing that the plants could survive fairly well below it and just grew like mad toward anything they perceived as greater light .... the edges. If you grow an annual vine and study it, you'll be amazed at how they seem to not only have eyes, but brains. They seem able to develop strategies for survival and domination. They can be very sneaky, underhanded and surprising!

    Bookmark   November 21, 2013 at 5:08PM
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Dino the next thing you could do is try and incorporate temperature into your experiment. I have to disagree with Yard about temperature of Hawaiian sand would get very hot, however my beautiful Gulf Coast white sand does not. So maybe you could do just sand based on its color? You see how this could lead to a lifetime of become a college professor!

    Bookmark   November 22, 2013 at 10:44AM
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Thank you for the replies; they are definitely helpful. I need to do more research for sure, but the project is only one month long and I need to run with the results I have for now. Just to explain what I did, I used 7 different types of landscape coverings/mulch along with a control. If you look at the top picture, I had 8 sections each 29" by 11.5". After that I transplanted 16 samples in each (middle picture). I then layered about 2" of each material on top of that, as you can see in the bottom picture. I repeated the same test for seeds.

    Bookmark   November 24, 2013 at 1:23PM
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The surprising result I got was the plants covered with the gravel, black mulch, and sand all had no survivors. I did not expect gravel to be so effective. Only 3 plants survived pine needles, which was surprising since I thought pine needles were loose and lightweight.

    Bookmark   November 24, 2013 at 1:26PM
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