Experimenting with Growth Mediums for Microgreens: Coco Coir vs. Paper Towels
(Disclaimer: this is not intended to be business or health advice, read the end of the blog for more info.)
In the realm of hydroponics and indoor farming, the choice of growth medium is one of a few critical factors that can significantly influence the health, growth rate, and yield of plants. Two such mediums, coco coir and paper towels, have been the subject of debate among gardening enthusiasts and professionals alike. To shed light on their efficacy, in 2020 we conducted an experiment to compare these mediums in a controlled environment, focusing on the cultivation of Radish Microgreens. This video has now become one of our Top 3 most popular YouTube videos for Microgreens on our channel, with over 500,000 views.
The experiment was designed to evaluate the performance of Long Scarlett Cincinnati Radish Microgreens grown in coco coir versus those grown on paper towels. Coco coir, a by-product of coconut husks, is renowned for its water retention and aeration properties, making it a popular choice among hydroponic growers. On the other hand, paper towels, an unconventional choice, offer an intriguing combination of affordability and simplicity for many home-growers.
The experiment was conducted over several days, with observations and adjustments made as needed.
Here's a breakdown of the process and findings:
- Tray Setup: 1 no holed 1020 tray, 1 mesh 1020 tray, 1 no holed 1020 tray.
- Seed Quantity: Each tray was sown with 25 grams of Long Scarlett Cincinnati Radish Microgreen seeds.
- Germination Period: All trays underwent a 4-day germination process, of 3 days under weight and 1 day in blackout.
- Consistent Treatment: Throughout the test, every tray was given the same care and conditions.
Days 2 - 3 Observations:
- Coco Coir Germination: Exhibited strong germination with initial roots (radicles) effectively penetrating the medium.
- Paper Towel Germination: Showed signs of germination, but with less radicle penetration compared to coco coir. Seed Loss in Paper Towels: Noted a higher rate of seed loss due to inadequate radical penetration into the medium.
- Continued Growth in Coco Coir: Maintained healthy germination and growth, with effective radical development.
- Challenges for Paper Towels: Faced significant seed loss as many seeds failed to drive their radicles into the medium, affecting potential crop yield.
Day 5 Observations:
- Coco Coir Trays: Exhibited robust growth. One tray required additional water due to slight drying.
- Paper Towel Trays: Showed slower growth with signs of stress, such as reddening in the stems, likely due to dehydration.
Day 6 Update:
- Coco Coir Trays: Nearly ready for harvest, showing true leaves.
- Paper Towel Trays: Starting to catch up in growth, with a potential decent harvest expected.
Harvest Day (Day 8):
- Coco Coir Trays: Produced a healthy and tall crop, with some true leaves indicating readiness for harvest.
- Paper Towel Trays: Despite some germination issues, a surprisingly successful growth was noted, marking a first in our history with paper towels.
Harvesting from coco coir was straightforward using a harvesting knife, although some medium attached to the stems required washing. Paper towels presented a challenge due to less medium for roots to grip, necessitating careful cutting to avoid pulling out roots.
Harvest Weights & Costs:
- Coco Coir Tray 1: 410 grams
- Coco Coir Tray 2: 435 grams
- Paper Towel Tray 1: 292 grams
- Paper Towel Tray 2: 210 grams
422.5 grams = Average harvest weight Coco Coir (410 + 435 = 845 ÷ 2 = 422.5)
250.5 grams = Average harvest weight Paper Towel (292 + 210 = 501 ÷ 2 = 250.5)
The cost for coco coir was mentioned to be approximately 78 cents per 1020 tray for the brand of coco coir used in the experiment. Considering the additional costs associated with the use of coco coir, such as the need for nutrients and the potential for higher water usage, the total cost per 10x20 tray was estimated to be around $1.50.
In contrast, the cost for using paper towels was cited as being around $0.01 (one penny) per tray, depending on the brand used.
- Coco Coir: Showed a very healthy root structure with minimal issues.
- Paper Towels: Had some areas of poor germination but overall healthy growth.
- Coco Coir: Taller crops with a healthy appearance and minimal undergrowth.
- Paper Towels: Less height but good uniformity and healthy cotyledons, despite some yellowing indicative of stress or deficiency.
A blind taste test revealed no significant difference in flavor between crops grown in coco coir and paper towels. Both exhibited the characteristic spicy kick of radish microgreens.
Conclusion and Recommendations
The experiment's findings were quite revealing, with each medium showcasing its strengths and weaknesses. Here's a more detailed conclusion based on the observed results:
Coco Coir: The Preferred Medium for Consistency
Coco coir proved to be a reliable medium, offering a balance of moisture retention and aeration that facilitated robust plant growth. The Radish Microgreens grown in coco coir trays not only germinated more uniformly but also developed a stronger root system, which is crucial for nutrient uptake and overall plant health. The ease of harvesting and higher harvesting weights made coco coir the preferred choice for this experiment.
Paper Towels: A Surprising Contender with Potential
Despite initial skepticism, paper towels emerged as a surprisingly viable medium. While they did not match the performance of coco coir in terms of growth speed and ease of management, they demonstrated potential for certain applications, especially considering their cost-effectiveness. The paper towel medium could be particularly appealing for small-scale growers or educational purposes where cost constraints are a significant factor.
Given the promising results with paper towels, further research is recommended to optimize their use. This could involve:
- Testing Different Brands: Identifying which brands of paper towels offer the best balance of water retention and root penetration.
- Exploring Other Crops: Determining if the success with radishes can be replicated with other crops, especially those with more delicate root systems.
- Refining Germination Techniques: Improving the germination rate on paper towels to match that of coco coir.
An additional aspect worth considering is the environmental impact of each medium. Coco coir is a renewable resource but often requires significant shipping distances, which can increase its carbon footprint. Paper towels, while convenient, can contribute to waste unless sourced from recycled materials. Future experiments could include a lifecycle assessment to understand the full environmental costs of each medium.
In conclusion, while coco coir stands out as the more robust and user-friendly medium, the low cost and unexpected success of paper towels cannot be dismissed.
When considering paper towels as a growth medium, it's important to be mindful of the potential presence of chemicals like bleach, used in the manufacturing process for whitening. These substances could impact plant health and the safety of the produce. Therefore, we recommend growers should select unbleached, chemical-free paper towels to ensure a safer cultivation environment. Despite these concerns, using paper towels can be an engaging and educational method for growing plants, offering a fun way to experiment with hydroponic techniques and indoor gardening. As with any growing practice, making an informed decision that aligns with personal and safety standards is key.
*All information found within this blog is based off of our 2020 YouTube video "Can Paper Towels Grow Microgreens Successfully? | Coco Coir vs Paper Towel". Please note that the mentioned costs and prices may vary due to changes in the cost of goods since the creation of this video, as well as differences in the brands of items used. This was a single experiment and is not meant to be a complete conclusion of potential results. This is also not intended to be used as health, environmental or business advice.*