Coring-injection method of applying compost to Christmas tree plantations

Final Report for FNE12-764

Project Type: Farmer
Funds awarded in 2012: $13,491.00
Projected End Date: 12/31/2014
Region: Northeast
State: Vermont
Project Leader:
Fred Salo
Northeast Kingdom Christmas Trees
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Project Information


As Christmas tree farming has evolved into plantation style farming, potential issues with disease and soil health have developed, including increased disease and death from Armillaria, and a decrease in soil fertility and organic matter after multiple harvests. Due to observations on our tree farm in VT, we hypothesized that compost additions may benefit overall tree health and market value. A core injection method of compost application was developed to address potential issues with disturbing the tree roots.

Two different locally available composts were used in this trial: Compost A was obtained from a dairy farm; Compost B was commercial compost with a more regimented culturing process. Both composts outperformed the control in important tree measures, specifically, shoot length, bud count, color and density. The effects were more drastic in the second and third year of application, though the control also increased over time in most cases. Compost A outperformed Compost B in most of these measures, though these differences were small and may not be significant, as compared to the differences between either of the composts and the control.

In contrast, mortality rates were lowest with Compost B treatments, and further research on tree mortality would be beneficial. This study demonstrates the efficacy of using the core injection method to apply compost to Christmas trees. Application of compost may increase tree vigor and commercial value, increase soil health, and decrease the need to synthetic fertilizers and pesticides over the length of an operation.

Each compost treatment area was 5 rows (30’) wide and 70 trees (350’) long and received 27 cubic yards of compost. The application rate for compost was one inch thick in a 30 inch wide band in the space between tree rows which covered one-half of the total plot area. The average cost of compost application was $2.25 per tree (Compost A) or $2.75 per tree (Compost B) which included $1.25 per tree for application and coring. Compost A was less expensive to purchase at $26/yd ($1.00 per tree) than Compost B at $40/yd ($1.50 per tree) plus the delivery charge.

However, irrespective of cost, this study demonstrated there is value in applying compost. Specific kinds of compost application may also reduce tree mortality caused from Armillaria, but that result needs further investigation, as Compost A did not suggest this result. The mechanisms of compost benefits were not included in this study, but it has been demonstrated in other contexts that compost confers multiple beneficial features. These include inoculation of, and habitat for, beneficial soil organisms, addition of organic matter, addition and retention of slower release nutrients, increase in soil friability and increase in both water infiltration and retention.


Salomaa Tree Plantation operates on 277 acres, of which 93 acres are in the production of Balsam fir and Fraser fir for the Christmas Tree Industry. The Farm was started by Fred and Yolande Salo with transplant beds in 1980 and with the first planting in the field in 1983 of 15,000 trees. We have planted trees every year thereafter maintaining a balance of approximately 40 % Fraser fir and 60% balsam fir. We harvest between 5,000 and 10,000 trees annually. The current inventory exceeds 75,000 trees. We market most of the trees to Christmas tree dealers in the major Metropolitan areas (wholesale trade). We have all our production on our farm location in Stannard (no leased land or external farm location). Salomaa Tree Plantation is a full time operation that requires 1 to 3 people to maintain the farm, and with a seasonal increase to 10 or 12 people for November harvest.

We, Fred and Yolande, started a business as Landscape Contractors (design and build), in NY (1974). A small garden shop was then added along with an FTD flower shop. The farm was managed part time until 1989. During these years we experimented with using compost from Lederle Labs, Monsanto chemical. Their form of compost was free to landscape contractors. We found that odor was the biggest use problem. We never had it tested but found that a compost application prior to seeding a new lawn, on a plot where the builder had stripped and sold the top soil, would assure a beautiful healthy lawn (and to eliminate the odor one inch of top soil was added). Fred is a graduate of UVM, Business, and was a sales Engineer for a major Corporation for eight years, was a Certified Nurseryman on the board of Directors of the NY State Nurseryman’s Assoc. in NY State, and a founding member and a past President of the Vermont Christmas Tree Association.

Over the past 50 years growing trees for the Christmas tree industry has transformed from being a wild forest crop, growing naturally in the more mountains areas, to plantations with trees planted in rows and highly cultured. During these years the industry has grown to plus or minus 30 million trees consumed annually in the U.S. However, during this very productive period certain cultural problems have been noticed that could threaten the sustainability of at least portions of some farms. At the center of the problems is the fact that the organic make up of some soils is lacking or is being depleted over many rotations of growing trees, causing unhealthy soils and unhealthy trees that chemical fertilizers just will not cure. Unhealthy soils mean unhealthy trees that can die from diseases and lack the quality demanded by the buyers and at the same time encourage the over use of chemicals in the attempt to compensate for poor soil health.

As we encountered dead and dying trees on the farm we began to wonder what was causing their death. A number of possibilities arose, including Armillaria, planting too deeply, too much or too little water, or other poor soil health conditions. Armillaria is a parasitic fungus, causing root disease. All of these potential problems gave reason to wonder about soil health in general. We hypothesized that compost amendments might improve soil health and reduce tree mortality. Two experiments to support that applying compost to improve soil health were considered. An actual field trial was chosen (over a small plot test plot method) as being the best way to convince growers that applying compost is not only doable but will increase the value of their crop enough to compensate for the expense.

Adding compost to fields of planted trees has not been part of the recommended cultural practices. Sod and weeds killed with weed killers adds a good quantity of organic material and is sufficient for the first tree rotation and sometimes thereafter. Some fields of trees maintain health with these methods. If unhealthy soils do develop and a farm makes the decision to apply compost multiple challenges may arise in application. Rototilling is not an option because rototilling destroys roots. A surface application not only takes too long to be effective, but dragging a cut tree through compost is not desirable. Cost and availability of compost are other big issues.

Fir trees planted for Christmas trees have a normal crop rotation period of 7 to 14 years depending on the species, cultural practices and soil conditions (Balsam 7 to 11 years, Fraser 8 to 14). Salomaa Tree Plantation was started in 1980 and the original blocks (fields) of trees are currently ending the 3rd and beginning the 4th rotation. Three problems have evolved. 1. The blocks that were cleared with a bull dozer and rock rake have always produced trees that lack dark green color and cannot demand a premium wholesale price. 2. The blocks in their 3rd rotation lack the luster of the prior rotations and 3. These same blocks (3rd rotation) are having more dieback. Some of this more serious die back and death of trees has been diagnosed as Armillaria root rot fungus that has become a major problem in Christmas tree plantations. Continued die back and producing trees of reduced quality will cut heavily into the financial bottom line and could actually place the future of any Christmas tree farm and the future of the industry in jeopardy. It should be noted that plantation grown Christmas trees is a relatively new industry in Vermont. With a slow start in the late 1950’s, and 1960’s many farms today have not been active long enough to experience what I refer to as the - “rotational problem.”(Several rotations of growing trees using up the organic material)

Applying compost to soils to grow other crops has become a common cultural practice. Costs have been reduced, fungus problems have been minimized, and on some farms chemicals use has been completely eliminated. These crops are maximizing quality, commanding top prices at market and are create a more environmentally friendly business model. Christmas tree growers should consider following these practices.

The question came up as to how you add compost to an existing block of trees without hurting the roots by cultivation and get it to the root zone so it could go to work quickly. The main problem is how to apply compost to existing blocks of trees that have trees of different ages growing. A common practice by most growers is to interplant the existing block with new transplants two years prior to the harvest to accelerate the next crop rotation. If the farm waited for the field to be completely harvested to add compost then three years would be added to each rotation, which would decrease farm profits. Adding compost between the rows mixing with a rototiller would tangle with roots and do more damage than good. We developed a coring-injection method that seemed to solve these challenges (See Intro-Methods pdf for pictures).

Project Objectives:

A field trial using the coring injection method for compost application was used as a demonstration to show Christmas tree growers that they can add compost to their acres of trees. This application could solve soil health issues, caused by lack of organic material, result in healthier trees, reduce fungus diseases, enable less chemical use and potentially reduce the production cycle time. We projected the grower would see an economic return and the environment would benefit from reduced chemical application. The community will benefit from this reduced chemical use but also from a sustainable farm that adds not only beauty as a working landscape but also economic gains from hiring workers and more local spending.

This project demonstrates how to add compost to established stands of Christmas trees by top dressing and incorporating the compost using a turf core aerator. This removed 2 to 3 inch cores the size of the index finger and the added compost was brushed into the holes with any remainder on the surface to be leached in by rain. This placed compost very close to roots without hurting them, used less compost, kept costs down, and theoretically improved the organic content of the soil (soil health improvement), which we hypothesized would result in healthier, more robust looking trees.


There is a lack of literature investigating whether Christmas tree composting in the Northeast would have a positive effect on growing Fir trees. Several projects in other areas, including Europe, seemed more concerned with getting rid of sewer sludge and landfill compost than actually increasing profitability and sustainability on the tree farm. A North Carolina project in 1999 showed that adding compost did not help reduce Phytophthora root rot, a disease problem found in wet soil conditions. Several projects noted that more time was needed to measure the response to compost. Projects did not include adding compost to the soil but rather used the top dressing technique as a form of treatment. Projects seemed to be administered by research scientists, very technical in nature, and lacked practical field trials that would have to be exhibited before most growers would be willing to try the concept.

The approach offered by this farm is to recognize that changes could occur to the chemical and physical makeup of the soils and should be monitored including soil pH, organic matter (OM) content, and nutrient levels. We recognize two beneficial aspects of applying compost that may be overlooked: 1. Ability of compost to hold more moisture during the drier season, 2. Compost will also suspend chemical fertilizers. Fir trees are classified as shallow rooted and heavy rains can leach fertilizer through the root zone before the roots accept it. Retention of fertilizer and water in the root zone with compost application is not only environmentally beneficial it also may yield better tree color.

An important aspect of applying compost is that over several rotations of growing trees the existing soil is lacking or has used up certain important qualities of soil ecology. A hypothesis passed on to this project by one of our experts is that cleared and cropped forest soils change over time, eliminating essential factors, most likely related to the micro-flora and fauna that reside in forest soils. Inoculating compost with native forest soil may also be beneficial, but is not explored in this project. However, compost can serve as a biological inoculant for trees.


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  • Jeffrey Carter


Materials and methods:

Compost Choice and Application:

Understanding these facts about composting and recognizing the problems with applying compost to an existing block of trees we developed the following method. We believe this method is innovative, environmentally friendly, will over time be economically feasible, and the economic returns will exceed the expenditure of time and compost cost. The economic return will contribute to sustaining farms that might stop growing trees because of the declining ability to produce trees profitably.

We specifically focused on compost, recognizing that many of the larger Vermont Christmas tree farms are not close to urban landfills or sewage plants. We used two local compost sources: farm compost produced by Michaud dairy farm in East Hardwick VT (Compost A), and engineered compost, manufactured by Highfields Composting in Hardwick, VT (Compost B). Both sources of compost were lab tested for future comparison with results between the two kinds of compost. Dairy farm compost is more readily available to most growers in Vermont and costs less per yard, with less trucking cost. However it is generally not as weed free as the engineered compost is. As the makeup of compost can vary it needs to be closely monitored.
The first choice, Compost A, was from a source considered to be of acceptable quality and has a track record of producing compost from the farm’s own source of cow manure. It was also offered at a lower price than other producers. This compost was not under cover at the dairy farm, probably had less wood mulch in contributing to density, so it was heavier than Compost B. The delivery truck had to make two trips to keep within the weight limits. By volume it exceeded the forty eight yards ordered but because it did not spread as easily there was no excess compared to Compost B.

Compost B was engineered compost from Highfields Composting, a mix of materials from manure, hay, waste products from restaurants, wood mulch, and other. It is monitored carefully, turned when required and overall more carefully prepared. Because of this process most weed seed is killed and is very user-friendly. However, some soup spoons, clam shells and bones were still present.

Three separate trial blocks were used so that there were three replications of the compost treatments and the control (Blocks I, II and III). Each treatment in each block had the same length and width. Compost was applied between the rows of trees (see Intro-Methods pdf for pictures). The three treatments were adjacent to each other so that all three together make a rectangle shape block, Block I, II and III. Block IA, IIA, and IIIA received compost A with the aerator. Block IB, IIB, IIIB received compost B with the aerator. Block IC, IIC, and IIIC received neither the compost nor the aerator. All trees were taken care of the same way with normal cultural practices. Each compost treatment area was 5 rows (30’) wide and 70 trees (350’) long and received 27 cubic yards of compost. The application rate for compost was one inch thick in a 30 inch wide band in the space between tree rows which covered one-half of the total plot area. The average cost of compost application was $2.25 per tree (Compost A) or $2.75 per tree (Compost B) which included $1.25 per tree for application and coring. Compost A was less expensive to purchase at $26/yd ($1.00 per tree) than Compost B at $40/yd ($1.50 per tree) plus the delivery charge.

These two choices of compost were made as a way to compare sources that are available in this area. In another area someone might not have these choices. Other sources such as municipal landfills may be an obvious choice because of cost. But then one might have to incorporate manure to create that “perfect mix”. If composting the trees proves successful, this farm will remove humus from a thirty year old “stump dump” here on the farm, import raw manure and create our own compost.

Several machines were experimented with before this particular Classen® unit proved to do the best job. Weight was a factor along with the split tines allowing for the necessary “adjusting” turn capabilities in the row.
Aeration with this type machine is relatively easy, respecting the need for a good operator. Level, flat ground will be the easiest, with uneven ground a bit more challenging. That is where the split tine design helps. The machine will have the tendency to dart and weave and some core holes will not be maximum depth of three inches. It was found that ground speed was difficult to regulate. Sod or moss cover will inhibit the depth of core also. One has to remember that coring alone offers benefits. Aeration for sure, but allowing water, fertilizer, lime and in this experiment, compost, to leave the ground surface is important. It will also help with compaction or crusting of the surface.

It was first thought that compost could be spread with a VICON fertilizer spreader behind a small Kubota tractor. This did not work because the consistency of compost varies, had clumps and can be very wet. Small manure spreaders of various types were considered but were ruled out because they would not drop the compost in place at a controlled rate/thickness. Compost costing $25 to $50 per yard (plus delivery cost) does not allow for careless use. Turf-grass managers have sophisticated top dressing machines but because there are no rentals locally we did not try one. No matter which approach was used the hopper would have to be refilled mid row, with five gallon buckets. With that in mind dumping and spreading with a rake worked well enough, and actually helped work the compost into the holes.

Sampling for soil testing was taken from the center two treatment rows so as to reduce cross-contamination between compost types. The data collected from the trees were only taken from the center thirty-five trees of the inner three rows of the five rows treated (total 105 trees per treatment), leaving one row of trees on each side as a buffer to prevent possible cross-contamination of compost types.

Treatment and Block Analysis:

Soil moisture was measured with a soil moisture probe, and aerated composted treatments had greater soil moisture. Compost samples were sent to the University of Vermont Agriculture and Environmental Testing Lab for analysis (summary of results can be seen in Table 1, see Result pdf). Compost A weighed 836 lbs per cubic yard and was 68.2% total solids. Compost B weighed 660 lbs per cubic yard and was 59.4% total solids. A comparison of the two compost tests shows that Compost A had more N, P, and K than Compost B.
Soil samples were sent to Dairy One for analysis. The soil test results indicate that the soil is very low in phosphorus, potassium, calcium, and magnesium. Soil samples were also sent to the Cornell Nutrient Analysis Lab for a Cornell Soil Health Test (CSHT). While it is more costly than a regular soil test, it also provides a complex approach measuring not only the chemical properties but also the physical and biological properties. Analyzing a CSHT can result in a better understanding of one’s soil. Results from the CSHT can be found in the Result Figures pdf (Table 2 and 3). CSHT samples were taken to examine differences between the three blocks, and between the three composts. The average overall quality score was 77.9 compost A, 65.0 for compost B, and 70.4 for the control group.

Tree Measurements:

All trees to be measured within each block were tagged and numbered. There were 105 marked trees per treatment per block. Compost was applied in early April and measurements taken in July every year. Measurements were taken in 2012, 2013 and 2014 after annual growth was complete. Ten different characteristics were chosen for the study. These characteristics are important for Christmas tree growers, and would indicate tree growth and vigor and market value. Trees were also checked for disease. The most important characteristics became apparent over time: shoot length, bud count, color, and density. Only these four measures were taken in 2014 and these measurements are summarized in the results. Other measurements taken the first two years are detailed in the Appendix along with individual graphs of each measurement (another way to visualize the same data).

Trunk diameter was measured with a caliper one inch above the ground. Shoot length of the tree in inches was the shoot in the barrel mid height. Density refers to the amount of foliage on a tree, and was scored as low, medium and high. More dense trees demand more money. Bud count was scored as the number of buds on the same shoot used to measure shoot length: a score of 1 was 0-5 buds, a score of 2 was 6-10 buds and a score of 3 was 11-15 buds. Color refers to the color of the foliage of the tree, and was a simple rating of light, medium or dark (dark maximum being about Benjamin Moore forest green 2047-10 color). A light color can indicate poor health while a dark green color indicates good tree health. Leader length was the length of the main leader prior to shearing and was scored 1 for more than 12 inches, or 2 less than 12 inches. Number of leaders was the number of buds on the main leader prior to shearing and was scored as 1 for less than 10 buds and 2 for 10 or more buds. Terminal buds were counted on the terminal of the main leader prior to shearing.

Research results and discussion:

Tree Measurement Results:

Shoot Length

Average shoot length increased the most between 2012 and 2013, for both Compost A and Compost B (Figure 1, Results pdf below). The control actually averaged slightly greater shoot length than Compost B in 2012, but was less than both composts in 2013 and 2014. While the compost appeared to affect shoot length in 2014, the differences in the treatments were not as great as in 2013.

Bud Count

Average bud count was similar across all treatments for the first year (Figure 2, Results pdf). However, in 2013 and 2014 average bud count was greater for both of the compost treatments than for the control. These effects were greater in 2013 than in 2014. Compost A had slightly greater number of buds than Compost B in both of these years. The bud count results suggest the second and third year have greater bud development than the first, regardless of the treatment.


Average color scores for Compost A increased yearly, while Compost B color scores were greatest in 2013 (Figure 3, Results pdf). Both compost treatments had greater average color scores every year as compared to the control. The differences between the control and the composts were slightly greater in 2014 than in 2013.


Average density score differences between the compost treatments and the control were the greatest in 2014 (Figure 4, Results pdf). However, during 2014 all treatments had increased density irrespective of treatment. In both 2013 and 2014 Compost A had slightly greater average density scores. The density results suggest that the third year of growth is markedly different, regardless of treatment.

Treatments By Blocks

This data is also summarized with the effects of each block (see Tables 4, 5, and 6, Results pdf). In general, irrespective of treatment, block III outperformed the other blocks. These differences were most noticeable in shoot length averages. The average number of dead trees in 2014 was slightly lower with the Compost B treatment than with either Compost A or the control.


Both Compost A and Compost B appear to provide benefits to Christmas trees which may result in greater health and marketability. The compost tests show a higher nutrient value for Compost A than B, and the Cornell Soil Health Test shows a better soil health rating for the area in which Compost A was used than where Compost B was used. These measures correspond with the results that generally suggest Compost A outperformed Compost B. However, the difference was not as great as the difference between either one of the composts and the control, suggesting that differences between the composts might not be significant. Contrarily, Compost B had a lower average mortality rate in 2014 and a higher color score in 2013. It was observed that Compost A promoted annual weed growth and Compost B did not, which makes sense because Compost A was not processed commercially. It is possible that weeds grew from seeds from Compost A and competed for nutrients with the trees, though this factor didn’t seem to outweigh the positive benefits Compost A conferred to tree vigor on trees that were not dying. Dairy farms are a dominant agriculture practice in Vermont, and this study suggests that dairy compost can be used to improve soil health.

The year 2012 was the only year that the control had a greater average value for any measurement than the composts, and the first year in general did not show as great of a treatment effect as did 2013 or 2014. This suggests that there may be a lag time between compost application and tree response. Additionally, this response is probably related to tree growth timing, as even the control averages increased over time for most measures.

Further studies may consider more specific density measurements for more precise results. Research might also increase block replication or a priori designations based upon soil characteristics (as block III had greater averages for most results), other farms, or longer time periods. Statistical analysis of measurements was beyond the scope of this study, but may be useful in future analyses. Economic analysis of compost cost and application as compared to the benefits demonstrated by this research in increased tree health may also be useful for growers when deciding when it is most advantageous to apply compost.

However, irrespective of cost, this study demonstrated there is value in applying compost. Specific kinds of compost application may also reduce tree mortality caused from Armillaria, but that result needs further investigation, as Compost A did not suggest this result. The mechanisms of compost benefits were not included in this study, but it has been demonstrated in other contexts that compost confers multiple beneficial features. These include inoculation of, and habitat for, beneficial soil organisms, addition of organic matter, addition and retention of slower release nutrients, increase in soil friability and increase in both water infiltration and retention.

Participation Summary
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.