Final report for OS17-106

Developing Sustainable and New Alternative Non-chemical Weed Control Strategies for Container Nursery Growers

Project Type: On-Farm Research
Funds awarded in 2017: $15,000.00
Projected End Date: 03/14/2019
Grant Recipient: University of Florida
Region: Southern
State: Florida
Principal Investigator:
Dr. Stephen Christopher Marble
University of Florida/Institute of Food and Agricultural Sciences
Expand All

Project Information


Five trials were conducted at four locations in central Florida in 2017 and 2018 [Dover (2 separate trials), Ruskin, Balm, and Apopka FL) to determine the efficacy of different mulch types on weed control in container nurseries. Mulch treatments included 1) pinebark mini-nuggets alone; 2) pinebark mini-nuggets applied in combination with M-Binder mulch tackifier (Granite Seed Co., North Lehi, Utah) 3) hardwood-mulch (derived from the invasive Melaleuca tree species) alone; 4) hardwood mulch applied in combination with tackifier; 5) recycled newspaper slurry alone; 6) recycled newspaper slurry used in combination with pinebark nuggets; 7) sawdust applied alone; and 8) sawdust applied in combination with the tackifier. Treatment (9) involved seeding pots with annual ryegrass seeds (Lolium multiflorum) at a rate of 30 lbs. per acre, allowing seed to become established for 6 weeks, and then applying a contact action herbicide (diquat) before seed development to evaluate residue as a weed control tool. A plastic mulch was also evaluated which was comprised of cutting a white on black plastic sheet (white side up) and securing around the entire base of the plant, covering the media surface. These mulch treatments were compared with two control treatments, the first being a chemical control of one of the most commonly used preemergence herbicides [OH2 Ornamental Herbicide (oxyfluorfen + pendimethalin), Everiss, Inc., Dublin, OH] applied at the standard recommended label rate. A non-treated control (no herbicide or mulch) was also used for comparison at all locations with the exception of Ruskin for comparison. Growth of Podocarpus macrocarpus (podocarpus), Ulmus parvifolia (elm) and Ligustrum japonicum (ligustrum) were also evaluated. All mulch treatments significantly reduced weed growth in comparison with the non-treated control. The sawdust and herbicide treatments were the only treatments that did not significantly reduce handweeding time. Across all trial locations and years, plastic and pine bark treatments resulted in the greatest reduction in weed biomass (79 to 97% reduction) and a 66 to 91% reduction in hand weeding time. No growth differences were observed on any of the evaluated species. Results of this study demonstrate that mulch comprised of plastic or pine bark nuggets could be an effective weed management tool for several long-term nursery crops.

Project Objectives:

The objective of our trial is to evaluate use of mulch as a long-term (multi-month) weed management strategy and compare performance of mulch materials to a commonly used preemergence herbicide or use of no weed management method (non-treated control). The goal of this project was to determine the efficacy of these different mulch materials as well as develop a guideline for growers in terms of using mulch more effectively for weed control and provide cost estimates for using mulch in comparison with preemergence herbicides, the industry standard. 


Click linked name(s) to expand
  • Greg Shiver
  • Vincent Tort


Materials and methods:

In 2017, trials were conducted at two container nurseries in Hillsborough County, Florida including J&R Nursery in Dover, FL and Sun City Tree Farm in Ruskin, FL. Trials were initiated on April 25, 2017. At both locations, treatments (Table 1) were applied to container-grown ornamentals. Treatments originally planned included 1) pinebark mini-nuggets alone; 2) pinebark mini-nuggets applied in combination with M-Binder mulch tackifier (Granite Seed Co., North Lehi, Utah) 3) hardwood-mulch (derived from the invasive Melaleuca tree species) alone; 4) hardwood mulch applied in combination with tackifier; 5) recycled newspaper slurry (described previously by Cline et al., 2011) alone; 6) recycled newspaper slurry used in combination with pinebark nuggets; 7) sawdust applied alone; and 8) sawdust applied in combination with the tackifier. The last mulch treatment (9) annual ryegrass seeds (Lolium multiflorum) were sown at a rate of 30 lbs. per acre, allowed seed to become established for 4 weeks, and then sprayed with a contact action herbicide (diquat) before seed development to evaluate residue as a weed control tool. These mulch treatments will be compared with two control treatments, the first being a chemical control (11) of one of the most commonly used preemergence herbicides [OH2 Ornamental Herbicide (oxyfluorfen + pendimethalin), Everiss, Inc., Dublin, OH] applied at the standard recommended label rate of 100 lbs. produce per acre (112 kg per ha). A non-treated control (12) (no herbicide or mulch) was also used for comparison and to determine percent control (fresh weight reduction) from aforementioned treatments.

Table 1. Mulch treatments applied to container-grown ornamentals at 2 locations in Central Florida.

Mulch Material


1. Pinebark nuggets (PB)

Applied at 2 in. (5 cm) depth

2. Pinebark nuggets + M Binder Tackifier

Applied at 2 in. (5 cm) depth

3. Hardwood mulch

Applied at 2 in. (5 cm) depth

4. Hardwood mulch + M-Binder tackifier

Applied at 2 in. (5 cm) depth

5. Newspaper slurry

Applied at 0.5 in. (1.3 cm) depth

6. Newspaper slurry + Pinebark nuggets

Slurry applied below PB mulch layer at depths described above

7. Sawdust

Applied at 1 in. (2.5 cm) depth

8. Sawdust + M Binder tackifier

Applied at 1 in. (2.5 cm) depth

9. Ryegrass mulch

Applied at 30 lbs. per acre. Germination was poor so treatment was excluded from analysis

10. Herbicide (OH2)

Applied at 3 mo. intervals (2 times) to mimic standard grower practices

11. Nontreated control

No treatments applied

12. Plastic mulch

Added to trial based on grower interest. Plastic bags placed over pots (Figure 1).

In Dover, treatments were applied to 15 gal. (57 L) container-grown podocarpus (Podocarpus macrophyllus). In Ruskin, treatments were applied to 25 gal. (95 L) elm trees (Ulmus parvifolia). Ryegrass sown as a living mulch had poor germination at both locations, likely due to high temperatures; therefore, this treatment was excluded from analysis. In cases where the M-Binder tackifier was used, it was applied on top of mulch treatments at a rate of 150 lbs. product per acre (68 kg ha) based on manufacturer recommendations. An additional treatment was added in Dover based on grower interest. Plastic was draped over pots and secured with tape (Figure 1). No control (non-treated) was used at the Ruskin location due to grower preference.

Figure 1. PB = pinebark, PB+T = pinebark+tackifier, HW = hardwood mulch, HW+T = hardwood mulch + tackifier, NP = newspaper slurry, NP+PB = newspaper slurry + pinebark, SD+T = sawdust + tackifier; PM = plastic mulch, HERB = herbicide, CNTL = control.

Treatments were replicated 4 times at each location and single pots represented an experimental unit. The trial was designed as a completely randomized block design with location within the container nursery pad serving as the blocking factor. Data on weed control were collected monthly. Each month, pots were handweeded and time to handweed each pot was recorded. Following handweeding, all weeds from each pot were weighed to determine weed fresh weights in each treatment. At the time of trial installation, plant growth was assessed on podocarpus by taking growth indices [(plant height + plant width1 + plant width2)/3] and elm size was assessed by measuring height and caliper. Soil moisture was monitored using Hobo SMx-M005 soil moisture sensors connected to a HOBO datalogger (Onset Computer Corp., Bourne, MA). Weed and growth data were subjected to ANOVA using SAS software and post hoc means separation accomplished using Fisher’s LSD (0.05).

In 2018, these trials were repeated in Dover and in Balm (Wimauma) and Apopka, FL with installation at all locations occurring on April 19. In Balm and Apopka, Ligustrum japonicum were potted into 7 gal. (26.5 L) containers from trade (3 L) containers. The same mulch treatments and data collection procedures described previously were followed in 2018. However, as ligustrum liners were uniform in size at trial initiation, no initial growth measurements were recorded and only final measurements were taken.

Data were subjected to a mixed model analysis of variance with location, year, and block (rep) as random variables and treatment as a fixed variable. This allowed the analysis of all treatments across all dates and locations to determine the most effective mulch treatment. As the tackifier had no significant effect on results when comparing a mulch with or without the tackifier, the data from treatments containing a tackifer were pooled with like mulch materials that did not contain the tackifier. Data were analyzed to determine the differences in hand weeding time and weed biomass by month and cumulatively over the entire study. Decagon soil moisture data was plotted for illustration purposes and standard errors were added to the graph. Growers at Sun City Tree Farm had to lay down their trees in September of 2017 in order to protect their stock from damage due to Hurricane Irma. As a result, some of the mulch that was applied to trees in Ruskin was removed from pots. Therefore, only data through September were analyzed from that location.

Research results and discussion:

Weed Control. Weeding time was low at both 1 and 2 MAT but increased sharply at 3MAT, coinciding with higher rainfall that is typical for Florida in the summer months (Figure 2). Control (weed biomass) decreased at 4 MAT and then stayed relatively constant for the remainder of the trial. All treatments reduced weed biomass relative to the nontreated at 1 MAT but by 2 MAT the sawdust treatment had similar weed biomass as the nontreated (Table 2). It is also important to note that the herbicide treatment provided a benefit through 3 MAT but was similar to the control group on all other evaluation dates.

Figure 2. Means and standard error bars for weeding times across all treatments by month after trials were initiated (MAT).


Table 2. Mean weed weights by month after treatment (MAT) in mulch treatments.



Weed Weight (g)


Mulch type









4.3 b

27.6 b

66.6 bc

21.2 abc

33.8 bc

60.7 ab


Pinebark (PB)

0.3 b

9.8 b

12.5 c

12.2 bc

18.0 c

27.2 bc



4.1 b

8.2 b

72.9 bc

14.5 abc

41.7 bc

36.4 abc


PB + Slurry

0.5 b

8.6 b

8.7 c

21.8 abc

4.8 c

13.0 bc



3.0 b

63.8 a

82.5 b

29.4 ab

62.1 ab

42.4 abc



0.7 b

2.4 b

3.3 c

0.0 c

6.2 c

6.9 c



3.8 b

12.0 b

63.2 bc

39.8 ab

58.6 abc

41.8 abc



15.2 a

77.8 a

249.4 a

45.8 a

99.0 a

79.0 a


*Means within a column followed by the same letter are not significantly different (Fisher’s Protected LSD, P < 0.05).



When examining total weeding time, the plastic treatment provided the most benefit, however treatments containing pine bark (pine bark alone or pine bark + slurry) resulted in similar reductions in weeding weed (66 to 91% reductions). Sawdust and herbicide were the only treatments that did not significantly reduce weeding time (Table 3; Figure 3). All treatments significantly reduced weed biomass relative to the non-treated, but again, the plastic treatment and pine bark treatments provided the greatest benefit.

Table 3. Cumulative mean weeding time and weed weight (collected monthly) in mulch treatments over 6 months.



Weeding time




Mulch type

Total time (sec)

% Reduction of control


Total wt. (g)

% Reduction of control



48.7 cd



171.5 b



Pinebark (PB)

28.7 de



  70.3 c




49.9 bcd



124.9 bc



PB + Slurry

25.4 de



  46.9 c




59.3 abc



225.8 b




 7.5 e



  10.0 c




81.4 ab



188.2 b




84.0 a


333.3 a


*Means within a column followed by the same letter are not significantly different (Fisher’s Protected LSD, P < 0.05).



Figure 3. Mean weeding time and standard error by treatment across all locations and evaluation dates.


Plant Growth. Plant growth was largely unaffected by mulch treatments (Table 4). For all three species, all mulch treatments resulted in plants with similar growth rates or size compared with the non-treated control group. Minor differences were observed amongst mulch treatments with podocarpus and elm height, but differences were not observed visually and were potentially the result of differences in liner quality or other cultural practices.

Table 4. Effect of mulch treatments on mean increase in growth parameters including growth indices (Dover) and height and caliper (Ruskin) at two locations in Florida







Growth Index

(% increase)


(% increase)


(% increase)

Growth Index



Pinebark nuggets

  15 abw

21 ab




Pinebark nuggets + M Binder tackifier

24 ab

23 ab




Hardwood mulch

15 ab

21 ab




Hardwood mulch + M Binder tackifier

9 b

29 a




Newspaper slurry

25 ab

15 b




Newspaper slurry + pinebark nuggets

17 ab

15 b





12 ab

13 b




Sawdust + M Binder tackifier

29 a

28 a




Herbicide (OH2)

19 ab

24 ab




Plastic mulch

20 ab



Nontreated control

11 ab



z Podocarpus growth was measured by calculating percent increase in growth index = [(plant height + plant width1 + plant width2)/3] in Dover, FL. Height = tree height to highest growing point. Caliper measured at 6 in. above soil line. Height and caliper were measured on elms in Ruskin, FL.


yElm growth was measured by calculating percent increase in tree height and caliper on Elm in Ruskin, FL. Caliper was measured on all trees using digital caliper measurements taken 6 inches from the soil line.


xLigustrum growth was measured by calculating growth index at the conclusion of the study. Means were pooled across two locations (Balm and Apopka, FL).


wMeans followed by the same letter within each column are not significantly different according to Fisher’s protected LSD. Columns with no letters indicate no significant difference between treatments.



Soil Moisture. Due to system malfunctions, soil moisture data could not be analyzed statistically due to lack of replications with some treatments. However, soil moisture levels remained relatively constant and within acceptable levels for most of the study (Figure 4). Moisture sensors were also placed on the opposite side of drip emitters and were on the top 2in. of soil, which also contributed to lower moisture levels than might be expected in some cases. Most mulch treatments resulted in higher volumetric water content compared with non-mulched controls throughout the experiment but the increase in soil moisture did not correspond to increased growth.  

Figure 4. Soil moisture levels under each mulch layer averaged bi-weekly across two trial locations.


As illustrated with cumulative weed biomass, all of the mulch materials evaluated provided a reduction in weed growth in comparison with the non-mulched control. For the entire six months of the experiment, treatments containing pine bark or the plastic mulch tended to provide the most benefit. Several other treatments provided more significant reductions in weed biomass or handweeding time, but the benefit was only realized in early evaluation periods. For example, hardwood, the slurry, and the herbicide treatment provided a benefit through 3 MAT but were similar to the non-treated at 4 MAT. For hard wood, the small particle size of the shredded wood material held more moisture, which likely contributed to greater weed germination. The same was true for sawdust that also held more moisture and decomposed more rapidly than pine bark. The herbicide treatment provided a benefit through 3 MAT but was less effective than some other mulch materials by as early as 4 MAT as it would have needed to be reapplied at approximately three months to continue to provide a benefit. The slurry provided a high level of control through 2 MAT but by 3 MAT, the material shrunk (Figure 4), exposing a large portion of the container media surface which reduced weed control. Adding the slurry to pine bark also did not provide any additional benefit compared with use of pine bark mulch alone.

Overall, growers wishing to use mulch for long-term weed control in container production could utilize pine bark nuggets or potentially wrap pots in plastic. Both of these mulching methods reduced weeding time and weed biomass by 60 to over 90% compared with using no mulch material at all and outperformed the use of a single preemergence herbicide application. While these treatments were the most effective, other mulch materials that were evaluated also provided a benefit and could potentially be utilized. The costs for these materials will likely be highly variable depending upon availability and grower location. The material cost for pinebark was about $0.16 per #7 container at 2 inches deep, hardwood was about $0.12, and plastic cost was about $0.023.  This would not include the labor to apply the materials. In comparison, material costs for a preemergence herbicide range about $0.008 to $0.012 per application to a seven gallon pot. However, in most cases preemergence herbicides are broadcast at a cost of approximately $200 per acre and up to 80% of the material falls in-between the pots.  In Florida, during the spring-fall growing season, a preemergence herbicide application would be applied approximately every 5-6 weeks to maintain expected weed control. Other ongoing research at the University of Florida has shown that mulch particle size and depth are more important to weed control than mulch type. Thus, other mulch materials not evaluated here could also be utilized if they were available and processed in large (> 0.75 in.) particle sizes and did not hold high levels of moisture. An additional consideration is that these mulch materials were applied at approximately a 2 in. depth in all cases. This was difficult to accomplish on-farm as growers will typically completely fill pots to maximize root volume, and there will be no container “lip” to hold mulch materials on the media surface. In very large containers, growers could potentially utilize a labeled herbicide immediately after potting and then topdress pots with mulch once soil had settled. In very large containers, leaving a shallow rim in containers for mulch application would likely have little to no impact on overall plant growth, but this has not been thoroughly investigated.


Due to small sample size available in 2017, few statistical differences were noted among the treatments, especially when considering growth data. However, as this was designed to be a 2-year trial, additional data points will allow us to better determine the effects of these mulch treatments on both weed control and ornamental crop growth. We also determined that adding tackifier to mulch significantly increased the amount of mulch that stayed in the pots, especially for the sawdust treatment in which some of the mulch blew away once it dried. Additional data points are also needed for moisture sensor data due to two incidences when loggers malfunctioned or were dislodged from pots following hurricane conditions. Trials for 2018 are schedule to be installed at the two grower locations on April 17, 2008 and will follow procedures described above. In addition to trials at grower farms, the experiment will also be repeated at the Gulf Coast Research and Education Center (using funds from Dr. Marble’s program) to display at the field day if pots from grower locations cannot be moved for the field day. While this trial will be used primarily for educational purposes, it will be replicated and data will be collected as described above to provide us additional data points in a more controlled environment and also to provide additional data for publishing in a peer-reviewed journal article.



Participation Summary
2 Farmers participating in research

Educational & Outreach Activities

6 Consultations
3 Curricula, factsheets or educational tools
3 On-farm demonstrations
3 Online trainings
1 Tours
4 Webinars / talks / presentations
1 Workshop field days

Participation Summary

111 Farmers
7 Ag professionals participated
Education/outreach description:

An educational field day for nursery growers was held on October 18, 2018 at the University of Florida/IFAS Gulf Coast Research and Education Center in Balm, FL. At this field day, growers toured research plots and were able to inspect each of the mulch treatments and examine ligustrum growth. All growers were given a handout (see attached) that summarized research results from the mulch trials across all trial locations and years. Growers from seven different nursery operations were in attendance. 100% of all attendees increased their knowledge of ornamental plant production, 71% of growers indicated they would alter their current weed management practices to improve control and utilize the integrated weed management methods that were discussed, 100% gained new knowledge on new weeds and weed control methods, and 71% indicated they would be or would consider using or trialing one or more of the mulch materials that were demonstrated.


In addition to the field day, six different nurseries, not in attendance at the field day, were visited for consultations about incorporating use of organic mulch materials in their operations. Four locations were in central Florida while one was in south Florida (Loxahatchee) and one was in north Florida (Havanna). In several cases, the growers had a tremendous amount of ground wood material following Hurricane Irma in 2017 and Hurricane Michael in 2018 and were looking for weed control options in long-term crops or chemically sensitive crops. Results from these experiments were shared and weed management programs for each nursery were developed.

Results of these trials were shared at three different locations in Florida (Tallahassee, Gainesville, Seffner) with over 100 nursery growers in attendance combined across all three locations.

The experiments/trials that were conducted at the different grower locations in Dover and Ruskin, FL were also used as demonstrations for those growers or others visiting those farms.

Results of the trial were incorporated into online Weed Management Courses offered through the University of Florida. These courses were offered in 2017 and 2018 and had over 60 grower participants from the U.S. and four other countries.

A video demonstrating the trial and the trial results is currently being developed.

Results from this trial were presented at national scientific and extension conferences including the Weed Science Society of America national conference in New Orleans, LA in February 2019 and will be presented at the 2019 National Association County Agricultural Agents (NACAA) in summer of 2019. Support from Southern SARE was recognized in all instances.


Learning Outcomes

71 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key changes:
  • Growers who attended the field day or were visited during consultations were able to see the results of these on-farm experiments and how mulch can be used to reduce weed control costs in container nurseries. As a result of field days and other training opportunities, 71% of growers indicated they would consider incorporating mulch into their current production. During consultations, 4 of the 6 nurseries that were visited began using mulch or started using mulch more extensively in their operations to improve weed control and reduce handweeding costs. While the use of mulch can significantly improve grower profitability and reduce hand labor costs, eliminating or significantly reducing preemergence herbicide applications provides additional environmental benefits. When granular herbicides are applied to spaced containers, as is conventionally practiced in large container production, over 80% of the herbicide applied falls in between containers and is not available for weed control in the crop. Growers that utilize mulch will be able to reduce or eliminate use of preemergence herbicides in some of these cases, further saving on chemical costs and increasing environmental quality and potentially improving water runoff quality. Long-term learning outcomes and impacts will continue to be assessed as adoption increases in the future.

Project Outcomes

4 Farmers changed or adopted a practice
2 New working collaborations
Project outcomes:

Overall, this project was highly successful in terms of impact for growers and adoption, which is already occurring. Growers were able to see the results of the trial at the field day or were given handouts or viewed photos during classroom in-person presentations. As the trials were concluded in late 2018, we have not yet fully disseminated the results to a broad audience, but currently over 200 growers or green industry professionals have seen the results of these trials and observed how different mulch types can improve weed control. We can verify that four large container operations in Florida have already implemented mulch into their production systems partially as a result of this research project while a high percentage of those in attendance at various trainings indicate they plan to also incorporate or at least consider, incorporating mulch into their production.

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.