Vermicompost vs potting soil: experiment #1

Okay, so you always hear of the studies about the different soil types with fertilizer X or compost Y.  But what does it really mean??? I set up a small “scientific” experiment to get a concrete results of a comparison of my vermicompost to normal potting soil.  The results are shown in photos below.


Using a vermicompost mix will still benefit plant growth even when using commercial potting soil.  The results may not be as impressive as when vermicompost is compared to regular soil, but there should be a noticeable difference.


I started on January 12th with two pots of premium potting soil. This was a store-bought product. I filled one planting pot with only this soil. In the other, I put the potting soil with a 20% mix of vermicompost (usual recommended amount). In each pot I placed 4 flower seeds (dwarf thumbelina zinnias).  Since the whole experiment was performed in winter, I placed the pots under sunlight bulbs to provide the proper amount of “daylight” and warmth. Then I waited….

Potting Soil Sprouts coming up 1 week later

Potting Soil Sprouts -7 days

On 1/19 I noticed that three of the potting soil seeds had sprouted compared to 1 in the vermicompost pot. A few days later all the seeds that were going to germinate had done so. There were 3 plants in each of the pots.

17 Days into experiment

Sprouts all beginning to grow -17 days

17 days in: The sprouts are getting larger. Note: the pot with the gray duct-tape V is the one with the vermicompost mixture… I know, I know it is not very scientific labeling but we make due with what we have.

Plants 19 days into experiment

Plants 19 days into experiment

Here we are 3 days later (19th day) the plants are growing more and more.  The vermicompost plants are slightly taller and have a little bit bigger leaves.  The difference is not too impressive though

39 days in - vermicompost plants are slightly bigger

39 days in - vermicompost plants are slightly bigger

Photo above shows experiment 39 days in. Comparing tallest to shortest the vermicompost plants are bigger. Right now, the advantage of the vermicompost still seems to be small.

47 days Vermicompost plants are taller

47 days Vermicompost plants are taller

Photo above depicts plants after 47 days. It is clear that the vermicompost plants are growing taller and and leaves are larger. Now I am regretting placing all the seeds in a single pot. They are crowding each other too much. If I run experiment again, I will use individual pots. Also noticing that the soil is drying out quicker overall. I imagine this is since the plants are so much larger now. But one other notable difference is that the vermicompost soil is holding the moisture longer than the potting soil.

Vermicompost experiment after 53 days

Vermi-plants are fuller, healthier looking after almost 2 months.

After 53 days, the vermicompost plants (on right) are still taller, but also appear to be fuller. There are more offshoots from the stem. Note the one coming off the largest plant, it is going to produce another bud.

Potting soil plant flowers

Potting soil plant flowers

Vermicompost plant flowers

Vermicompost plant flowers

62 Days into experiment

62 Days - I declare vermicompost the winner!

The above photo shows the final results after 62 days. Notice that the potting soil plants (left) did eventually grow taller, but they did not match the height of the vermi-plants. Also the vermi-plants have more offshoots (4) and leaf growth too. See the biggest offshoot is reaching up to the lamp. It has another flower forming on it.

One last photo with measuring tape….

Measuring the results

Measuring the growth results


In conclusion, I believe vermicompost resulted in numerous benefits to the plants. first, the increased growth was demonstrated in the photos. The largest vermicompost plant flower reached over 1 foot in height. The next highest flowers were 10.5,  8.5, and 8 inches. With the potting soil plants flowers reached 9.25, 8.75, &  6.5 inches.

Not only did the vermicompost seem to increase the plant height, but there were more flowers and fuller plants. From the photos the vermi-plants had 6 offshoots where-as the potting soil plants had only 3 (one on each plant). This is what lead to fuller plants and more flowers. Letting the plants continue to grow will result in these offshoots flowering and producing more beautiful plants.

And lastly, the vermi-plants had better water conditions. The soil remained moist for longer periods of time compared to the potting soil. I added the same amount of water to each pot, but several times I found the potting soil plants starting to wilt. The vermi-plants did not have this issue.

In general, I believe there was a realistic benefit to using the 20% vermicompost mix. I only wish I used bigger or separate pots for each seed. I think that plant growth was hampered slightly as they grew larger by overcrowding of the soil.

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2 Responses to Vermicompost vs potting soil: experiment #1

  1. Carolyn says:

    Hi Steve,

    Nice experiment. It also seemed that the pink flowers on the vc plant were a brighter or deeper color than the one in the potting soil. I transplanted some marigolds into a bed of regular soil, but threw in a couple handfuls of vc. In addition to growing 2x as big as the flowers that were already in the bed, the flower heads were bigger and were a more vivid color.

    I appreciate when I see more worm composters actually doing these experiments that not only back up the more scientific ones, but lend more credibility of the product to others.

  2. gards says:

    nice experiment man, to the point and easy to follow thanks:)