Honey Plant Intercropping on Christmas Tree Farms

Final report for FNE19-925

Project Type: Farmer
Funds awarded in 2019: $10,032.00
Projected End Date: 02/28/2021
Grant Recipient: Humming Grove Farm
Region: Northeast
State: Connecticut
Project Leader:
Richard Cowles
Humming Grove Farm
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Project Information


There are many reasons to establish high-yielding honey crops as interplants within Christmas tree plantations: the crops are mutually compatible, there are probably pest management benefits from increasing plant diversity, and honey can add a second stream of revenue.  However, establishing these plants, mostly small-seeded mints, can be very difficult.  Planting seeds directly provided virtually no establishment of these species and would be a very expensive and inefficient approach.  We found that reduction in herbaceous cover with glyphosate in the fall, followed by planting seedlings from plug trays, use of SureGuard herbicide, and composted wood chip mulch comprised a program that allowed these plants to become established.  Many of the high-yielding honey crop species were judged to be inadequate, including bird’s-foot trefoil, creeping thyme, and figwort.  The exceptional plants were all of the mountain mint species, agastache, and wild mint.

Project Objectives:

(1) This project seeks to establish intercrops of honey plants within a Christmas tree planting.

(2) This project seeks to measure inputs required for establishing and maintaining these intercrops. Inputs will include cost of seed and any herbicides used to favor the establishment or to maintain the intercrop.

(3) This project seeks to measure the honey bee activity within the different intercrops over a growing season: this will serve as a surrogate for measuring honey yield from specific intercrops being tested, because honey bees can forage for several miles from their hives and cannot be caged on these crops to measure honey yield.

The information gained will permit other growers to establish plantings most compatible with their specific objectives (e.g., bee forage and honey income, support for natural enemies of insect pests, fixing of nitrogen, and/or reduction of vegetation management costs).


Armored scale management: Armored scales are the most challenging arthropod pest affecting Christmas tree production along the East Coast. These insects have two generations per year, and can build to high populations if left unmanaged. They cause yellow spots to form on the needles; under extreme conditions the color is completely bleached and the needles may appear mottled with white or brown (Cowles 2011). Growers currently manage scales by spraying systemic insecticide on the base of the trunk of the tree, which selectively kills armored scales (Cowles 2010). The basal bark spray method does not contaminate surrounding flowering vegetation with the insecticide active ingredient, dinotefuran, which is highly toxic to bees. Dr. Carole Cheah (CAES, Valley Laboratory) is investigating mass rearing of Chilocorus stigma, the twice-stabbed lady beetle, for release in Christmas tree plantations for biological control of these armored scales (Cheah 2016).

Fixed land honey production: The idea to plant seeds of nectar-yielding plants to boost honey harvests is an old idea. In the United States, within 30 years of the invention of the Langstroth hive, which permitted industrialized beekeeping, journals recorded the efforts of innovators to test plants for use in bee pastures (Root 1887, McLain et al. 1887). By 1900, beekeepers had noted that farm practices and urbanization were leading to reductions in flowering plant populations with associated reductions in honey yields, and were debating the value of cultivating honey plants (Williams 1900). It appears that the nay-sayers for cultivating bee pasture won, as the concept appears to have nearly disappeared through the 20th century.

During the 1980s, Dr. George Ayers at Michigan State University studied diversionary plantings of extremely attractive flowering species to divert honey bees away from apple orchards. His idea was to locate plantings far enough away from the orchards (with its problematic bee-attractive clover blooming in the grassy row middles) to prevent spray drift in the orchard from contaminating the diversionary crop (Ayers et al. 1991). Dr. Ayers came to realize that there was good potential for honey harvests from some of these plants, so they could be grown expressly for honey crops (Ayers and Hoopingarner, 1986). The potential yields of crops grown to produce honey was also studied and reported by agronomists at University of Massachusetts (Herbert et al. 1996).

More recent efforts have emphasized the use of cover crops, non-cropped areas and set-aside programs to enhance pollinator habitat (Decourtye et al. 2010). These authors ignored the practice through parts of Eastern Europe to cultivate honey plants expressly to support managed honey bees (Dr. Leo Sharashkin, pers. comm., Oct. 14, 2017).

Vegetation management

Intercropping within Christmas tree plantations has not been extensively investigated. Researchers have recognized the potential benefit of relay-intercropping to supplement Christmas tree farm income; however, using black plastic mulch to intercrop muskmelons slowed the growth of the trees (Lamont et al., 1993). An agronomist tested herb intercrops between rows of pines – some of these herbs are also plants well known to have high value to honey bees (https://agresearchmag.ars.usda.gov/1997/nov/tree), but did not appear to have published the results. An environmental group dedicated to reduce atmospheric carbon dioxide levels provides several justifications for tree/edible crop intercropping systems (www.drawdown.org/solutions/food/tree-intercropping), but does not describe any systems involving Christmas trees.

If we assume that Christmas trees are planted on a 5 × 6 foot spacing, require 7 years per crop, and are worth $50 apiece, the gross sales would average $10,000 per acre per year. Anise hyssop, Agastache foeniculum, is estimated to produce up to 2,600 pounds of honey per acre per year (Pan and Herbert 1997). Generally, honey bee activity over an entire season on a crop is directly proportional to the amount of honey yield from that plant (Ayers et al. 1991). In a direct comparison, a mountain mint, Pycnanthemum pilosum, had 3.5 times the number of visits from honey bees as plots of anise hyssop (Ayers et al. 1987). If half of the area of a Christmas tree plantation were planted to honey crops with yields similar to mountain mint, the maximum predicted yield should be close to 1,000 lb of honey per intercropped acre (in which about half of the area would be covered by the honey crop). Honey bees consume about half of the nectar that they gather (Al-Ghamdi et al. 2016), and so the net yield should be about

500 lb per acre. At $10.00 per pound (a reasonable retail value estimated for locally-produced honey), this would be worth $5,000 per acre.

This proposal is intended to simultaneously address several problems and missed opportunities:

(1) Three species of armored scale pests of Christmas trees are commonly found to cause economic damage to trees in the eastern U.S. Scales cause yellow spots to form on needles where they feed, and can cause the needles to drop. Currently, interstate shipments of Christmas trees from North Carolina to Florida ($15M annually) are threatened by the presence of armored scales (James Rockis, National Christmas Tree Board, personal communication). One farm in CT destroyed over $30,000 of trees in 2017 because they had become unsalable, due to injury caused by armored scales. Christmas tree growers currently depend on basal

bark sprays of systemic insecticides to manage armored scale pests, which can be effective but is costly. Armored scales can reach population densities of approximately 10 billion per acre, making the rare occurrence of favorable mutations leading to insecticide resistance a likely outcome. Dependence on one class of insecticide for scale management may lead to insecticide resistance and management failure. Armored scales have numerous natural enemies, including twice-stabbed lady beetles (Chilocorus spp.), another generalist scale predator (Cybocephalus nipponicus), and a parasitic wasp (Encarsia citrina), which have been observed to sometimes provide adequate control of the armored scale complex (elongate hemlock scale, hemlock scale, and cryptomeria scale) found in Christmas tree plantings where there is high ground cover plant diversity. Establishing high quality honey bee forage could also support these beneficial predatory and parasitic insects and consequently help to maintain low population densities of armored scales, balsam twig aphids, and spruce spider mites.

(2) Our landscapes do not currently have enough floral resources to support the health of honey bee colonies. This manifests itself in excessive competition among colonies, and weak colonies unable to defend themselves from hive parasites (small hive beetles) and predators (yellowjackets). Weak hives are victims of robbing behavior from nearby honey bee colonies, which transfers diseases and varroa mites between hives, and leads to poor honey yields and winter starvation. Growing bee forage in Christmas tree plantations could support 2 – 4 hives per acre.

(3) Current conventional Christmas tree vegetation management is labor, machine, and chemical intensive. Although the current grassy strips grown between rows of Christmas trees stabilize soil, they require considerable labor and machine time to maintain. An alternative system based upon flowering perennial vegetation growing in the row middles may only need mowing once annually, in the autumn.

(4) Christmas trees are a perennial crop that requires about seven years per production cycle. During the time that trees are growing to salable size, there is no revenue generated. Integrating high-yielding fixed-land honey production by intercropping honey plants within the confines of Christmas tree farms could generate revenue equal to half the value of the trees.

Description of farm operation:

We have been operating this farm for 4.5 years, but I have been involved with agriculture professionally for 40 years. From 2.5 acres, we sell up to 250 Christmas trees per year.


Click linked name(s) to expand
  • Dr. Jatinder Aulakh - Technical Advisor (Researcher)


Materials and methods:

Site preparation was attempted with fall (2018) application of glyphosate herbicide, followed by spring frost-crack seeding of high-yielding honey crop species.  This method was found to be inadequate for establishing most species.  The greatest success with this approach, based upon stands of the desired species, was with bird’s-foot trefoil, alsike clover, and creeping thyme.  Even so, with these species, excessive competition from remaining grasses will have to be mitigated with selective grass herbicides to be applied in 2020.

Improved growth of anise hyssop over a septic leach field indicated that improved fertility could enhance the growth and establishment of plug transplants.  Therefore, 19-19-19 fertilizer was applied at the rate of 2 lb per 1000 square feet (actual N) applied in mid-July, in preparation for replanting.  Glyphosate was applied to whole plots on July 10, 2019, using an application rate of 2% glyphosate (without surfactant, in the Mad Dog formulation), applied at a volume of 15 gallons per acre.

Replicated plots (three replicates) containing seven species were split into main plots consisting of wood chip mulch vs. no mulch conditions.  Three herbicide treatments (no herbicide, Plateau, SureGuard) were then randomized to each main plot, so that there was a split-split plot design.  Herbicides were applied on July 20, 2019, with a backpack sprayer equipped with a flat fan nozzle calibrated to deliver 15 gallons per acre.  Herbicides were applied into designated plots:  Plateau was applied at 6 mL in 1.5 gal of spray (2 fl oz per treated acre), and SureGuard at 17 g in 1.5 gal (6 oz per treated acre).  Wood chip mulch was applied as fresh chips of mixed conifer and hardwood species applied to a depth of 4 cm, up to and under the adjacent Christmas trees, on the side of the plot designated through randomization to receive the mulch treatment.  Wood chips were applied after herbicide application and immediately prior to planting plugs.  

Seedlings of the seven species started in plugs trays were then planted by mid-September.  The condition of the transplanted plugs was rated on October 16, 2019, by Dr. Aulakh, using a 0 – 10 scale for chlorosis or stunting, where the higher the value, the greater the degree of plant damage observed.  Data were subjected to analysis of variance using Statistix 9 software.


Research results and discussion:

The species planted varied in their ability to tolerate conditions resulting from being planted in a wood chip mulch and being exposed to herbicides.  For example, figwort (Scrophularia marylandica) was intolerant of mulch and was healthiest when competing vegetation was suppressed with SureGuard herbicide.  On the other hand, lemon balm (Melissa officinalis) was healthiest in the mulched plots, and did not tolerate either herbicide.  

A summary of the conditions favorable to establishing these species from plugs is given in the table below.  Ratings are as follows,  Maximum damage from stunting or chlorosis <1, ++; 1 – 2, +; >2, –; >5,– –.

  No mulch No mulch No mulch Mulch Mulch Mulch
Species No herbicide Plateau SureGuard No herbicide Plateau SureGuard
Agastache foeniculum — — ++
Mentha arvensis + + ++ + ++
Melissa officinalis + +
Scrophularia marylandica + +
Pycnanthemum pilosum + ++ ++
Pycnanthemum tenuifolium + ++ ++
Pycnanthemum muticum — — ++ + ++
Research conclusions:

Ideal conditions for establishing stands of high-yield honey plants that may also provide resources to the natural enemies of armored scales in Christmas trees are very species-specific.  Three species were found to establish good populations with autumn glyphosate site preparation, followed by frost-crack spring seeding: bird’s-foot trefoil, alsike clover, and creeping thyme.  Most of the remaining species were tolerant of fresh wood chip mulch without herbicide, with the exception of Agastache foeniculum and Scrophularia marylandica.  Most species were also tolerant of SureGuard herbicide when applied without mulch, with the exception of Agastache foeniculum and Melissa officinalis.  Agastache foeniculum appeared to thrive with the combination of mulch and SureGuard.  Melissa officinalis grew best with no herbicide, with or without mulch.  The remaining plants in the mint family, including three mountain mints, plus the Scrophularia marylandica, would best be established with no mulch but with the application of SureGuard herbicide.

Participation Summary
1 Farmer participating in research

Education & Outreach Activities and Participation Summary

2 Consultations
1 Curricula, factsheets or educational tools
1 Webinars / talks / presentations
1 Workshop field days

Participation Summary

65 Farmers
Education/outreach description:

A summer twilight meeting of the Connecticut Christmas Tree Growers’ Association was held at the Humming Grove Farm on June 26, 2019.  The interplanting of high yield honey crops and the potential ecological value of these crops for managing armored scales was discussed.  This project was also used for an educational program at the Connecticut Agricultural Experiment Station’s virtual Plant Science Day, in August, 2020.  The education video produced for that event can be viewed at https://youtu.be/rzyEyNf5CaU .  

Learning Outcomes

2 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

The key discovery from this project was that direct seeding is virtually impossible to accomplish in the drive row areas within Christmas tree plantations.  The reasons are (1) there is excessive competing vegetation, (2) tillage cannot be accomplished, because the roots of the Christmas trees are so shallow, and (3) the establishment from seed is extremely inefficient (and costly).  Therefore, the only practical way to establish the highest yielding honey crops is to plant them from plugs.  I anticipate that further propagation can readily done in succeeding years through sprigging of rhizomes, and so the only difficult period for establishing these plants will be in the first year.  Another grower, in New Jersey, will be following my recommendations for establishing honey crops in his Christmas tree plantation.

Project Outcomes

2 Farmers changed or adopted a practice
1 New working collaboration
Project outcomes:

This project has been very productive with respect to discovering what methods work for establishing various species of high-yielding honey crops, and for observing the responses of various species of pollinators to the plantings.  Certain species we tested are of questionable value for supporting honey bees:  (1) Bird’s-foot trefoil was found to be visited almost exclusively by European wool carder bees.  An additional concern for planting this species is that it may be an alternate host for phytophthora root rots, the most important disease of Christmas trees.  (2) Late figwort was found to initially only be attractive to Vespids, though later it was attractive to honey bees.  Again, later in the season it was principally visited by Vespids.  (3) Lemon balm was surprisingly unattractive to honey bees.  (4) Creeping thyme had tiny flowers and was not significantly attractive to honey bees.  (4) The great “winners” were all the species of mountain mints and the wild mint.  

Having the pollinator plants in place greatly reduced the effort and fuel used for mowing, as only half the area still needed to be mowed.  One final mowing was required before the sales season for Christmas trees, to allow customers to walk through the field.

Assessment of Project Approach and Areas of Further Study:

Observations were made regarding visitation by honey bees to the various plantings.  However, not all the plantings are even yet fully established, and it may take one or two more years of propagating the best of these species to have the full benefit of well established plants to provide nectar to the honey bees.  Further interactions suggested by this project proposal haven’t yet been investigated (such as benefit to natural enemies of armored scales in the Christmas trees) because the plantings need to be fully established.  

One other grower, in New Jersey, is planning to follow-up from this project to establish honey crop interplants among Christmas trees.  I am anticipating that the greatest use of the information gained from this project will be efforts by beekeepers to establish fixed land honey production with planned bee pastures.  However, one difficulty that may be insurmountable is that the honey crop is openly accessible to more than my own bee colonies.  Honey bees will travel up to two miles to exploit excellent forage, and since my farm is surrounded by commercial farms that rent bees, my own farm may only recover a small portion of the honey that is produced.

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.