my landscaping science project part 1

Dino_Rabbit(10b)November 20, 2013

I am helping my son to do a science fair project. He decided to test some landscape coverings to see which ones blocked out the most weeds. He 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 (we put three layers of that). This was done in South Florida (Zone 10B).
Thank you!

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"Black mulch" means nothing. What was that made of, plastic or something else?

In some instances the thickness of the mulch is what determines the effectiveness, not the material. If the mulch material effectively prevents the plants growing under it from access to sunlight those plants will not grow. I have had Tulips and Daffodils push their way up through 5 inches of shredded leaves so it also depends some on how much that plant wants to grow. 2 inches of most good mulch material is just barely adequate.

    Bookmark   November 21, 2013 at 6:32AM
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Black material absorbs sunlight and heats up. This raises soil temps above the germination temperature. If hot enough, is can kill tender or cool season plants.

Sand is not good for plant growth in that sand has very low water and nutrient capacity. Water and nutrients flow quickly through sand, faster than most plants can absorb them.

Mulch has the little to do in with suppressing establish weedy species. Mulch can encourage weeds already growing. How mulch controls weeds in smothering the seed in too much moisture, depriving the seed of oxygen, or blocking light from the seed. Many weedy species are called "early succession" plants. Those generally need light and moderate moisture to germinate.

    Bookmark   November 21, 2013 at 11:12PM
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This is the kind of black mulch I bought. It is made from some wood material, but it doesn't say what kind of wood it is made of. I don't know if it is made from cypress trees, pine trees, or any other types of mulch. I could not find anything on their website, but I might call them on Monday to find out.

    Bookmark   November 24, 2013 at 1:33PM
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