Controls on vegetable growth, flowering, and production of Hops in the Southeastern USA

Final Report for FS14-280

Project Type: Farmer/Rancher
Funds awarded in 2014: $8,834.00
Projected End Date: 12/31/2016
Region: Southern
State: Virginia
Principal Investigator:
Justen Dick
Kelly Ridge Farms, LLC
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Project Information


We applied several treatments to Cascade hops at Kelly Ridge Farms' hop yard (Meadowview, VA) in an attempt to affect vegetative growth and infloration timing.  These variables can directly control hop cone production per crown which is of critical interest to this industry.  Applied treatments included techniques to increase early soil temperatures, three different timings of early emergent shoot pruning, and two apical meristem manipulation treatments.  We attempted to survey regional growers for additional data and engaged local college students in the experimental process.  Our results were presented at meetings of regional hops growers and at the Association for Southeastern Biologist 2016 meeting.


The bulk of America's production of Hops (Humulus lupulus) has historically been limited to the Pacific Northwest. Several recent economic and cultural factors have conspired to spur an interest by the farming community in regional production of the crop: the recent explosion of the craft brewing industry; local-vore movements that encourage sourcing ingredients within a narrowly defined geographic area; and the environmental, financial, and regulatory considerations of shipping and preserving unwieldy amounts of vegetative material intended for consumption.

A major hurdle to production in the Southeastern United States is lower overall production per acre compared to that of traditional production areas. Virginia growers have estimated current average production per acre at about 25% of larger Western producers. The ability to achieve an adequate amount of vegetative growth prior to flowering is hypothesized to be a significant variable in this production gap.

There is significant economic incentive to solve this problem of yield. Locally sourced hops allow consumers to experience wet-hopped beers - a popular style that has been prohibitively difficult to procure for brewers that are separated by a distance threshold from established large producers. Brewers are able to have more quality control of their ingredients, as well as a line of communication for input with growers. Locally-sourced hops also reduce the additional costs and the increased carbon footprints associated with transcontinental shipping.  

Flowering in Humulus lupulus is controlled by a complex interrelationship of light, temperature, vegetative size requirements, and hormones. Hops require a vernalization period of approximately six weeks. It is a photoperiod sensitive plant which has been described as performing best between 35 and 55 degrees latitude; this is due to longer summer day lengths, which extend the vegetative growth that ultimately provides the platform for flower growth. Previous research indicates that the short day lengths and minimum internodal numbers/lengths (i.e. vegetative growth) that occur in autumn incur flowering. Increasing the period of vegetative growth and delaying the final flowering stage results in an overall increase of commercially viable yield.  Manipulation of these variables could also potentially contribute to affecting local flavor and characteristic/chemical variations contributing to a regional “terroir”. 

Several treatments for affecting these variables have been hypothesized.  Hop growers in South Africa have reportedly had success using phototherapy to delay hops flowering and increase production.  There is also anecdotal evidence that several Virginia growers have experimented with pruning treatments to delay flowering.  Plant hormones which control flowering are typically produced in the apical meristem (the tip of the hop bine). The removal or manipulation (inverting) of the apical meristem may favorably affect hormone concentrations and delay associated flowering. However, these experiments have yet to be performed with scientific rigor or to be adequately documented.

Region-specific research into sustainable and responsible manipulation of these and other variables could potentially narrow the production gap between eastern and western growers.  Theoretical successes may even allow a southward expansion of hops production into traditionally unfavorable areas (lower latitudes with shorter summer day lengths).  Such innovation could open up new viable crop options to southern farmers.

Project Objectives:

We evaluated three potential treatment types (a total of 7 discrete treatments) to affect vegetative growth and associated flowering timing in Cascade hops.  These were all designed to attempt to increase the amount of vegetative growth prior to flowering, either through promoting earlier vegetative growth or delaying the onset of flowering.  This was hypothesized to result in increased hop cone production.  Environmental, vegetative growth, hops cone production, and hop cone analytical data was collected to evaluate these treatments.  

We attempted to gather and document production data via questionnaires from regional growers regarding observed flowering and emergent shoot timing through the established regional growers organization Old Dominion Hops Cooperative.

We presented our results at two quarterly growers meetings of the Old Dominion Hops Cooperative in Charlottesville, VA. 

Our results were also presented by Emory and Henry Cooperators at the Association for Southeastern Biologists annual meeting in Concord, NC on March 31st – April 3rd, 2016

Students from Emory and Henry College (Primarily Emily Belanger) participated in research implementation activities throughout the summer collecting data and evaluating results, receiving an unique learning opportunity.


Click linked name(s) to expand/collapse or show everyone's info
  • Dr. Gerald Bresowar
  • Dr. Christine Fleet


Materials and methods:

Cascade hop crowns at Kelly Ridge Farms in Meadowview Virginia are planted in a total of twenty 50-foot sections.  Each section consists of approximately 16 to 18 hop crowns.  Each section was used as a base unit for different treatment groups and assigned an identification number between 1 and 20.  Treatment groups were established in a distributed pattern of sections to attempt to account for yard variations (elevation, horizontal position, etc). A total of seven treatments were evaluated for this project. 

One treatment group consisting of two sub groups (composed of three sections each) was selected for installation of hoop house treatments (fabric and plastic) in early spring. Hoop houses were installed March 16-18, 2015. Installation timing was selected to attempt to maximize early vegetative growth before growth exceeds hoop house height at first frost.  Once ambient temperatures were warmer, coverings were vented as needed manually to avoid overheating (100 deg F +).  The hoop houses were removed April 15, 2016 once shoots had emerged and significant vegetative growth was achieved.  All sections were trained to strings starting on April 24th.   

 A second treatment group (three sub groups, two sections each) was subdivided for application of early, middle and late emergent shoot pruning treatments. The prunings occurred on April 7th(early); April 14th-21st (middle); and on May 15th (late).

The third treatment group was subdivided into apical meristem pruning and manipulation (inversion) subgroups consisting of two sections each.  The manipulation of the apical meristem was performed by tying the tip in a downward position, in order to simulate reaching the top of the trellis.  These treatments were performed June 11 19, 2015 and were intended to occur about two weeks before flowering, after the bulk of vegetative growth had occurred. It was hypothesized that this would stimulate more lateral sidearm growth.

A fourth group was established as a control (4 sections).

The following environmental measurements were periodically collected during the experiments for each group:  Soil temperature (12” deep), ambient air temperature and humidity, and hoop house (both sub groups) air temperature and humidity.

Composite soil samples were collected from each section pre (4/30/2015) and post (4/21/2016) season and submitted to Virginia Tech's Soil Analysis Lab for nutrient analysis. 

Soluble nitrogen fertilizer (150 lbs/ acre) was applied starting on May 4th via drip fertigation system until flowering was observed.  

Vegetative growth data for each group was observed to determine the date of first shoot emergence and the date of flowering.  Measurements of average shoot height for each section were collected on May 13th and May 20th.  . On June 10th, just prior to anticipated flowering, more detailed vegetative growth data was collected including:  average internode length, total plant height, maximum sidearm width, and average sidearm width.  Cut bine lengths were measured during harvest on August 1st

Hop cone weight was measured during harvest for each section to obtain production data (lbs/section). Laboratory analysis of composite samples of hop cones from each section for alpha and beta acid content (the critical oils and resins in hops valued by brewers) was also performed at Virginia Tech.

In order to gather additional regional data regarding 2014 and 2015 crop shoot emergence and flowering timing, short questionnaires were prepared and distributed amongst the Old Dominion Hops Cooperative members in both hardcopy form during the Fall 2016 meeting.  An online survey was also submitted to the membership.  Finally, selected individual members were contacted directly in an attempt to gather data. 

Research results and discussion:

All treatments in this experiment were unsuccessful in altering flowering timing or first shoot emergence; all sections began flowering at approximately the same time on June 19th.  

Plastic hoop house treatments (and to a lesser extent fabric treatments) significantly raised air temperature 5-40 degrees F above ambient, but this did not appear to affect soil temperatures as intended.  Collected environmental data, depicted here soil-temperature-data indicates that neither hoop house treatment (plastic and fabric) was able to significantly raise soil temperatures. 

Later pruning dates may display a tendency toward increased sidearm width, as indicated in statistical analysis work by Emory and Henry Collaborators depicted here:  .hopposter-final.

Other treatments did not appear to strongly affect any of the measured vegetative growth critera (height, internodal length, sidearm width),  hops production, or acid /resin content.vegetative-growth-data

Soil nutrient data indicated all sections had adequate nutrients. soil-nutrient-analytical-data No strong correlations were observed between major nutrient flux and treatments.  There may be a weak trend of P and K nutrient flux with later pruning treatments.  One interpretation could be that there was increased nutrient uptake with later pruning dates.  

Soil nutrient data was much more variable than originally anticipated.  

We documented three data gaps during our experiment.  Fortunately in all cases,data gaps were spread across different treatment groups so that no total data loss occurred across any one treatment groups' sections.  Harvest vine length data was lost for four sections (17-20).  Hop cone weight data was unable to be collected for sections 18-20, due to cones being mixed with other sections prior to being weighed.  Finally, we failed to collect the laboratory analytical sample for section 2 prior to the hops being sold to breweries.  

We were unable to solicit any concrete responses from other growers in response to our questionnaires.  In the majority of cases, growers declined to participate in the survey.  Of those growers willing to respond, they typically had failed to adequately document precise dates of shoot emergence or flowering.  

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

We presented our results at two quarterly growers meetings of the Old Dominion Hops Cooperative in Charlottesville, VA. 

Our results were also presented by Emory and Henry Cooperators at the Association for Southeastern Biologists annual meeting in Concord, NC on March 31st – April 3rd, 2016 hopposter-final.

Students from Emory and Henry College (Primarily Emily Belanger) participated in research implementation activities throughout the summer collecting data and evaluating results, receiving an unique hands-on learning opportunity.


Project Outcomes

Project outcomes:

Our research indicates that hoop houses are ineffective mechanisms by which to attempt to manipulate hops vegetative growth or flowering timing.  Apical meristem manipulation also appears to be ineffective.  

Pruning timing was the only treatment that weakly indicated an effect on vegetative growth.  

This data suggests that the mechanisms we evaluated may not have as strong a role in vegetative growth or flowering than previously hypothesized. 

Soil nutrient data was much more variable than originally anticipated, which suggests further research into appropriate scales of soil management would be appropriate.  



Potential Contributions

The data we gathered will be very useful in guiding future research focus areas in non traditional hops regions. The collected soil also provides extremely useful baseline data to support ongoing nutrient recommendation  (Virginia Tech, North Carolina State University) in our region.  

Hops analytical data indicated relatively consistent alpha and beta acid content, which are important crop quality indicators.  Although we saw no significant differences between treatment groups, one benefit of these results is that they indicate that the final crop is a consistent product even with variations in horticultural conditions.  

Future Recommendations

Our results suggest that it may be beneficial to focus future research on the effects of pruning timing.    

Although hoop houses appear to be ineffective in raising soil temperatures to affect earlier vegetative growth, there may be other horticultural mechanisms that have not been evaluated to achieve the same result (elevated soil temperatures).  

Although apical meristem manipulation was ineffective in our experiment, other variables exist (such as different timings of the manipulation) that could be evaluated in future research.  

Phototherapy in hops as it relates to flowering timing and vegetative growth in hops remains an under-researched and potentially viable technique, albeit with higher capital costs.  

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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.