Peat versus Rockwool experiment.
The purpose of this experiment is to show what happens when a potting mix has a 'buffer' compared to when it is completely inert such as in Grodan stonewool.
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Shopping list
2 round containers
1 small bag of peat mix
1 small bag of Grodan Growcubes
An All purpose water soluble plant food
2 six-packs of 1" Petunias
Lemons/lemon juice
pH text kit or litmus paper
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- First prepare one six-pack of 1" Petunias as shown in the Grodan Growcube user guide
- Fill one container with your peat mix and one container with your Grodan Growcubes.
- Saturate both media with the exact same nutrient solution
- Plant 6 petunia in each container.
- You need to water the plants 1-2 times per week. Be careful always to mix enough nutrient solution, so that each time both containers receive the exact same amount of plant food.
How long does the experiment take? The rate of growth depends on light and temperature. Expect to wait 4-6 weeks to have enough growth for a comparison.
Our result
We did the experiment ourselves:
Petunias grown in a standard peat potting mix on the left and Grodan Growcubes on the right.
We fed a low 7-4-10 NPK solution, one to two times per week to each plant. Because you need much less fertilizer for your Grodan plant than for the peat plant, this small amount of fertilizer was ample to grow a healthy petunia plant on the right. However, the peat locked up much of the fertilizer, creating the small petunia plant on the left that is essentially starving. Peat also compacts over time, suffocating roots, unlike Grodan. |
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Other experiments to evaluate media.
Ultimately when evaluating which medium to choose or how well they perform there are two things that are important to look at: - How well are the roots able to utilize the entire volume of the medium ? Meaning do the roots grow throughout the whole medium. This can be tested by doing a rooting test
- When you fertigate (water with nutrient solution) will the solution spread throughout the medium, so the food reaches all the root tips? This uniformity test can be tested by doing a blue dye test
To find instruction on how to do these tests, please go to this page: test Your Rockwool.
You can use the same methods to test any medium against another. If you use loose media, put each of them in a long plant container.
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