To ensure a successful harvest and higher profits, a key step for many farmers is producing healthy vegetable transplants. In the North Central region, many organic growers have adopted the soil block method, believing it improves root development, but there has been little scientific research to back up these claims.
A new SARE-funded project, led by graduate student Anne Carey and faculty advisor Dr. Ajay Nair at Iowa State University, delved deeper into soil blocks. They evaluated the soil block technique against traditional plastic flats and tested five commercially available organic growing media to determine how they affected transplant growth.
Soil Blocks Vs. Plastic Flats
Organic vegetable growers are interested in the soil block method as an alternative to plastic flats, hoping to improve plant vigor and root development. Carey said that while anecdotal evidence exists, limited scientific research has been conducted to evaluate these claims.
Carey’s study aimed to compare the growth of cucumber and pepper transplants in both soil blocks and traditional plastic flats. They also evaluated four certified organic growing media and a standard mix to identify the best options for organic growers.
Key Findings
The study yielded some surprising results that challenge common assumptions about the soil block method.
- Varying Performance: Cucumbers grown in plastic flats had a significantly greater dry weight than those grown in soil blocks. In contrast, peppers grown in soil blocks had much higher dry weight than those grown in flats.
- Media Matters: The 'Cowsmo Green Potting Soil' stunted the growth of both cucumbers and peppers. However, the 'Beautiful Land Products', 'Purple Cow Organics', and 'Vermont Compost Company' media all produced healthy, vigorous transplants.
- Root Development: The research did not find a specific advantage to the root systems of plants grown in soil blocks.
Recommendations for Growers
The research provides valuable insights for organic growers in the North Central region looking to improve sustainability and profitability.
- Choose Wisely: Consider using soil blocks for pepper transplants but stick with plastic flats for cucumbers.
- Select Quality Media: All three of the top-performing media—'BLP', 'Purple', and 'Vermont'—are suitable for growing organic vegetable transplants. The regional products ('BLP' and 'Purple') can help farmers save on shipping costs and reduce their carbon footprint.
- Embrace Sustainable Practices: Using a durable, long-lasting metal soil block tool instead of disposable plastic flats provides economic and environmental benefits.
- Focus on Transplant Quality: Producing high-quality transplants leads to healthier crops and can increase economic returns for growers, regardless of the method used.
“High-quality transplants lead to high-quality crops, which sell for higher prices,” said Carey. “Having the opportunity to discuss transplant production with many growers and others throughout this project has given us a greater understanding of the challenges regional growers have in producing quality transplants. More information and continued research on soil blocks would be of great value, establishing optimal bulk density parameters and improving understanding of the impact this method has on vegetable transplant performance.”
Dig Deeper
This video series follows graduate student Anne Carey as she shares her findings and gives a hands-on look at the process of using soil blocks.
- In the first video, Carey offers an up-close look at the differences between soil block and plastic tray seedlings, highlighting variations in plant height and color. The video also touches on the different growing media being compared in the study and shares preliminary results.
- The second video provides a simple, step-by-step guide to making your own soil blocks.
- Finally, in the third video, Carey walks you through evaluating your own growing media to ensure a healthy, successful crop.