Summer Cover Crops for Organic No-till Broccoli

Progress report for FS20-326

Project Type: Farmer/Rancher
Funds awarded in 2020: $14,820.00
Projected End Date: 03/31/2022
Grant Recipient: Wild Hope Farm
Region: Southern
State: South Carolina
Principal Investigator:
Sarah Belk
Wild Hope Farm
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Project Information


While Shawn Jadnircek, the farm manager at Wild Hope Farm, has done some small experiments with sunn hemp and millet as summer covers for no-till fall-planted crops, we would like to conduct a more controlled experiment in order to examine what mix of sunn hemp, Japanese millet, soybeans and buckwheat result in the best weed suppression and yield for our fall-planted broccoli. If we find a successful mix, this would bring our no-till crops to 75% of our total production, increasing our ecological and financial sustainability as a farm business. 

In order to investigate which summer covers work the best, we will evaluate 1) weed suppression 2) total yields and 3) total labor hours for each treatment including bed preparation, transplanting and weeding.

Our experiment will consist of 5 treatments: 

1) Tilled after Sunnhemp (100lbs/acre)

2) Crimped Sunn Hemp (100lbs/acre)

3) Crimped Sunn Hemp (100lbs/acre) & Millet (50lbs/acre)

4) Crimped Sunn Hemp (75lbs/acre), Millet (50lbs/acre) & Buckwheat (50lbs/acre)

5) Crimped Sunn Hemp (75lbs/acre), Soybeans (50lbs/acre) & Buckwheat (50lbs/acre)

An area of 12 tractor pulled raised beds (217ft long) will be divided into 15 sections (3 beds wide, 54 ft each) in order to provide 3 replications of our 5 treatments. A list randomizer was used to assign each area a treatment.

Before planting, the 12-bed area will be stale seed bedded 1-2 times with mechanical cultivation equipment dependent on weather. Each cover crop will be seeded 3 beds wide with a bag seeder at the densities specified above, and then incorporated with another pass of the bed shaper.

Project Objectives:


  • Weed Suppression
    • After broccoli planting, weed counts will be conducted in each treatment area every 2 weeks until the end of harvest.
    • We will randomly pick three 5ft x 5ft squares to sample within the plot at each weed count. 
  • Labor Hours
    • Labor hours for the preparation, seeding, planting, and weeding will be tracked for each plot.
  • Total Yield
    • The total yield of broccoli in pounds will be tracked for each treatment. 


Click linked name(s) to expand
  • Katherine Belk - Producer (Educator)
  • Sophia Friis - Producer (Researcher)
  • Mark Dempsey
  • Shawn Jadrnicek - Producer
  • Rachel Klein - Producer


Materials and methods:


An area of 12 tractor pulled raised beds (217ft long) was divided into 15 sections (3 beds wide, 54 ft each) in order to provide 3 replications of our 5 cover crop treatments. A list randomizer was used to assign each area a treatment. Treatments were seeded with a bag seeder at the following rates:

Treatment 1: Tilled after Sunnhemp (100lbs/acre)

Treatment 2: Crimped Sunn Hemp (100lbs/acre)

Treatment 3: Crimped Sunn Hemp (100lbs/acre) & Millet (50lbs/acre)

Treatment 4: Crimped Sunn Hemp (75lbs/acre), Millet (50lbs/acre) & Buckwheat (50lbs/acre)

Treatment 5: Crimped Sunn Hemp (75lbs/acre), Soybeans (50lbs/acre) & Buckwheat (50lbs/acre)

The Plot Map depicts the randomized location of each treatment within our test plot. Broccoli plants were planted in each plot except for plots 4, 8 and 12 where we were short on broccoli transplants and supplemented the plots with cabbage and summer squash. 

Materials needed for weed tracking include a 5x5' square made from PVC pipe. Materials needed for harvest and yield tracking include harvest bins and knives for the harvest crew and color coordinated tape that correlates to each treatment in the field. In the plot, colored flags were attached to grounded stakes that indicated where treatments began and ended.



  • Winter rye and clover plot mowed and disked
  • Beds reformed with the bed shaper. 


  • Sections with treatment #1 and #2 seeded with Sunn Hemp (100lbs/acre)


  • Sections with treatment #3 seeded with Sunn Hemp (100lbs/acre) & Japanese Millet (50lbs/acre)
  • Sections with treatment #4 seeded with Sunn Hemp (75lbs/acre), Millet (50lbs/acre) & Buckwheat (50lbs/acre)
  • Sections with treatment #5 seeded with Sunn Hemp (75lbs/acre), Soybeans (50lbs/acre), & Buckwheat (50lbs/acre)


  • Treatment #1 sections flail mowed & disked


  • Treatment #1 sections tilled (2" depth) and bed shaped
  • All other sections terminated with roller-crimper


  • Same variety of broccoli transplanted in all sections using the mechanical transplanter with no-till attachment. Spacing at 2 rows, 12 inches.
  • 2 lines of drip tape laid per bed.
  • Treatment plots were marked in the field with colored flags.
  • Weed counts were conducted bi-weekly by laying the 5x5 square in the middle bed of each plot and observing weed coverage and weed type.


  • Harvest of broccoli began. All plots were picked 2-3 times a week and yield was tracked in pounds.
  • Harvest bins were marked with colored tape that corresponded to the treatment of that plot. A color key was posted in our wash station where yield by recorded in pounds in a chart that was then digitized for our records. 
Research results and discussion:

Weed Counts

A primary goal of crimped cover cropping systems is to suppress annual weeds. We assessed the effectiveness of our cover cropping through weed tracking. We tracked perennial & annual weed coverage in a randomized 5x5 plots in each of the treatments on a bi-weekly basis. We experienced significant cover crop regrowth & reseeding. The following Weed Count Graphs depict the % cover of weeds and cover crop regrowth/reseeding. Negative space in the graphs is shows properly mulched bed space and broccoli plant coverage.

In Treatment 1, sunn hemp alone did not suppress perennial weed growth at first. Over time the cover crop regrowth ultimately outcompeted both perennial weeds and broccoli. In Treatment 2, we experienced low suppression of both perennial and annual weed growth. In Treatment 3 we experienced high competition from both buckwheat reseeding and soybean regrowing. In Treatment 4, we believe the millet cover crop was water stressed prior to crimping so it did not effectively suppress perennial weeds. The presence of annual weeds was not significant. In Treatment 5, we experienced a great deal of buckwheat reseeding and sunn hemp regrowing.

Labor Hours

We tracked labor hours by treatment type and this bar graph shows how many times we had to visit the plot with the tractor.  The no-till plots required less trips which equated to less time and fuel needed to produce the crops.  The no-till numbers would have been even lower but we had to make several trips to mow the regrowth of the cover crop.  Hopefully we can properly terminate the sunn hemp and prevent those trips. 


Yields were highest in the sunn hemp and millet plot with a total yield of 0.249 lbs per bed foot. Overall, there was significant crop loss in the research plot due to transplant loss, Alternaria head rot and Bacterial head rot.

Cover and Cash Crop Behavior Observations

We experienced the regrowth of cover crops in most of the plots due to not timing the crimping of the cover crops sufficiently. At the time of crimping, the millet and buckwheat had produced viable seed and reseeded itself in the plots. The sunn hemp regrew from new growth points. This indicates to us a timing issue.

We experienced significant crop loss to disease. We also experienced heavy pest pressure in our greenhouses at the time of fall transplant production (particularly army worms) resulted in poor transplant vitality.

In the test plot, we experienced broccoli stem elongation possibly due to light competition from the cover crop regrowth. We flail mowed the tops of the sunn hemp in attempt to increase the broccoli’s light access. We knocked some broccoli stalks over during this process which resulted in further plant deformation. Cover crop regrowth possibly reduced air circulation and may have increased disease problems. Poor fall transplant production probably due to pythium, weak transplants affected growth in field.

Given our findings in the first year of this two year grant, we are making a few changes to our project methods so to ensure more robust broccoli transplants, properly crimped beds and hopefully the reduction of disease and pest pressure that may be altering the accuracy of our results. We're prioritizing early pest prevention in our greenhouses. These new methods will be outlined in our 2021 Methods  & Materials Report.

One last notable change is that in Treatment 5 (Crimped Sunn Hemp (75lbs/acre), Soybeans (50lbs/acre) & Buckwheat (50lbs/acre)) we are eliminating buckwheat from this mix so that we can crimp this treatment to the maturity of the soybeans. This treatment will also be planted three weeks earlier than the treatments containing buckwheat and millet. This alteration will give us more accurate data on the specific abilities of soybeans creating a sufficient understory of coverage in tandem with the sunn hemp. Our planting timeline will be as follows:

5/15/2021 - Treatments #1 and #2 seeded with Sunn Hemp (100lbs/acre).

5/24/2021 - Treatment #5 seeded with Sunn Hemp (75lbs/acre), Soybeans (50lbs/acre).

6/15/2021 - Treatment #3 seeded with Sunn Hemp (100lbs/acre) & Japanese Millet (50lbs/acre). Treatment #4 seeded with Sunn Hemp (75lbs/acre), Millet (50lbs/acre) & Buckwheat (50lbs/acre).

Participation Summary
5 Farmers participating in research

Educational & Outreach Activities

3 Consultations
3 Curricula, factsheets or educational tools
1 Webinars / talks / presentations

Participation Summary:

30 Farmers
Education/outreach description:

In November of 2020, to summarize year one of our research, facilitated a workshop at the Carolina Farm Stewardship Association 2020 Sustainable Agriculture Conference. This conference occurred virtually with a powerpoint presentation and opportunities for participants (approx. 30) to ask questions using the Zoom chat feature. The workshop lasted approximately an hour and was recorded for later access by conference participants.

Through our partnership with the Carolina Farm Stewardship Association, we consulted with Mark Dempsey throughout year one of our research. He studied the research plots with us days after crimping the cover crop and then a month later, after the broccoli had been planted. We discussed cover crop regrowth, possible disease apparent in the broccoli crop and cover crop management changes for next season. He also sat in on our CFSA workshop in November of 2020.

We created two visual representations of our research. A fact sheet describes our projects goals and a preliminary summary of results with images of our cover crop and graphs of weed counts to analyze the cover crop effectiveness. 

The second visual product is a seven minute video shot throughout the growing season and provides great visuals of our cover crop at all stages. This video describes the scope of our project and the benefits of cover cropping in a no-till agricultural system specific to the southeast. The video also includes conversation among our farmers, Mark Dempsey’s consultations, and possibilities to improve upon our experiment next season. The video was shown at our 2020 CFSA conference workshop. The video can be found here:

Learning Outcomes

40 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation

Project Outcomes

Project outcomes:

In regenerative, organic vegetable systems, cover crops provide several benefits to the producer - they prevent erosion, reduce water use, increase fertility, and improve the biological and physical properties of the soil. In addition to these benefits, cover crops that are terminated with the roller-crimper to produce mulch for the following cash crop can also provide a significant labor reduction for the farmer. Currently, 50% of our production is done in fall-planted rye and clover terminated for late spring planting. Most research in this area has focused on fall-planted cover crops, leaving little information about summer cover and prompting us to investigate further. With a longer growing season in the southeast, we have more of an opportunity to utilize summer cover crops. Having summer cover or mulch in place during the hurricane season (June-Dec) can significantly reduce damage and erosion to the field. Summer cover crops have the potential to reduce labor hours and increase soil resilience and retention in the southeast.

Information Products

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.