Does Treatment with Chlorella vulgaris Extend the Life of Tomato Plants to Increase Tomato Sales?

Final report for FS21-330

Project Type: Farmer/Rancher
Funds awarded in 2021: $14,640.00
Projected End Date: 03/31/2023
Grant Recipient: Sweetgrass Garden Co-op
Region: Southern
State: South Carolina
Principal Investigator:
Dale Snyder
Sweetgrass Garden Co-op
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Project Information



If these initial observations are valid, treatment with live chlorella vulgaris could make it possible to extend the life of tomato plants so that tomatoes can be harvested, where bacterial spot is endemic. Positive results will increase productivity and the length of the harvest period which will positively impact a farmer's bottom line.

Project Objectives:

The test garden site has not been planted with tomatoes during the previous 7 years.  It will be divided into 2 sections:  one will be treated with 3 inches of mushroom compost before planting, and with additional compost side dressing 4 weeks later.  The other section will be treated with chlorella vulgaris weekly beginning at the time of planting, 50,000 cells per sq foot produced on farm at Sweetgrass.   

Assignment of which section to treat with which amendment will be done by an independent observer.

It measures 32x32 ft (1026 sq feet), divided into four 16x16 ft test plots, which will be randomly assigned to the following treatments:
    1.   Algae
    2.   Algae + Compost
    3.   Compost
    4.   No amendment
The 25 plant tomato grid (let's call it the "tomato patch") in each of the 4 plots has 5 rows containing 5 plants.  The rows and plants are separated by 30 inches.   Each tomato patch is situated in a corner of its test plot so there is a 4 ft area between the edge-tomato plants and the edge of the plot.  That means 8 ft of separation between each of the tomato patches.   
There will be an untreated board barrier extending 10inches into the ground separating the 4 plots (essentially a 32-ft cross dividing the test garden into four equal-sized plots).
To reiterate the nomenclature:  test garden = 32x32 ft.  Test plot (four of them) = 16x16ft.   Tomato patch (four of them in the corners of the plots) = 12x12 ft.

Tomatoes: we will grow BHN1021.  Plants will be obtained from Banner Greenhouses (if plants are not available they will be grown from seed, started in our hoop house in organic potting soil).   There will be 25 plants in each of the test plots, planted at 24 inch intervals.   Lower leaves will be protected from exposure to the soil with organic matter (straw), and plants will be watered with drip irrigation (using our irrigation well).

In addition to determining whether there is resistance to bacterial spot, we will assess the effect of chlorella on nematodes and on soil health and bacterial activity determined by Haney testing.

End points:

1.Plant height

2.Plant vigor—a qualitative assessment by Zach Snipes (Clemson Extension Agent), blinded to treatment assignment. 

3.Onset of bacterial spot (adjudicated by Zach Snipes).

4.Tomato yield (also adjudicated by Zach Snipes), measured as tomatoes harvested per plant

5.Nematode testing in each test section (Clemson Nematode Lab)

6.Haney testing at the time of planting, and 2 months later (Ward Laboratories, Kearney, NB) 


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Materials and methods:


The effect of live chlorella vulgaris (algae) on plant growth and yield has been the subject of study since the 1970’s.  Its positive effect is attributed to production of growth enhancing compounds with foliar application, including auxins, gibberellin, and cytokinin.  In addition, with soil application, increases in soil microbial activity have been described, leading to increased organic matter and organic carbon. 

In this tomato study, we tested the effects of four soil nutrient approaches:   

1) live algae alone,   

2) algae plus compost, 

3) compost alone, and 

4) as a control, no soil amendment. 



The test garden was located on Johns Island, South Carolina, a barrier island with sandy soil described as Seabrook.  It was last tilled 5 years previously and was covered with native grasses and weeds.   

It measured 15,000 sq ft, and was divided into 8 rows, with each row divided into 4 sections, so there were 32 repeats.  

Each of the four treatments thus had 8 sections, and the treatments were randomly assigned by the agriculture statistics group at Clemson University.  Each of the 32 repeats was planted with 7 tomato plants separated by 18 inches. 

Tomato starts were from Bonnie Nursery in Nebo, NC. 48  plants per tray (2 inch plugs).   

Two tomato cultivars were planted from April 1 to April 5, 2021: Cherokee Purple (indeterminant), and  BHN 529 

(determinant).   Cultivar type had no influence on any of the 

variables measured and reported, so they are combined in this report. 

Compost was provided by Allen Skinner at Jacksonville, FL.  It was 

applied before planting by adding an 8 inch strip, 4 inches deep to the 

row, and it was lightly tilled in.   Side dressing of compost was applied 4 

weeks after planting.   Live chlorella vulgaris (algae) was provided by 

Enlightened Soil Corp (Johns Island, SC).   Algae were applied at a rate of50,000 cells per sq ft 

with a tank sprayer.  Half the application was directed to foliage, and half to soil within the drip line of the 

plant.  Algae were applied immediately after planting, then at 2-week intervals. 

There were no other chemical or organic inputs; e.g. no pesticides or herbicides were used.  Cardboard 

mulch weighted with wood chips was used between rows for weed control, and hoe and hand weeding 

was performed weekly.  

Spray irrigation was used as needed. 

Research results and discussion:

There was a high plant attrition rate.  Each of the 4 treatment groups had 56 plants at the beginning of the study, 

and at 3 months, the study groups had declined by 28%-36% (Table 1).  

We anticipated that most plants would succumb to bacterial spot whic is endemic in our area (that has 

been our past experience).  The months of May and June were unusually dry, so bacterial spot was rare, noted i

n 3 just plants.  The other plants died from Southern Blight, a soil borne fungus (Athelia rolfsii).  Since the 

distribution of plant loss was  uniform, we report yield per treatment block as well as yield per living plant. 

Table 1.  Distribution of plant loss:          

Live plants at 90 days: 

1.Control, no amendment40 plants 

2.Group 2, algae alone36 plants 

3.Group 3, compost alone37 plants 

4.Group 4, algae + compost36 plants 


Early soil testing: 

Soil testing was done by Ward Laboratories, Kearney, NE.  This included Haney testing, and 

measurement of microbial using phospholipid fatty acid analysis.  The first tests were done 

one week after application, before planting and before application of algae.  Thus, it is a measure

 of the contribution of the compost to fertility (Table 2) 

Table 2. Soil test results before algae application and planting. 

Haney testing 







CO2-C, ppmC







Haney soil 

health index
















Phospholipid fatty acids 


Total living microbial 

biomass (ng/g soil)

Total bacteria 


Total fungi 


No amendment









Of note, the PLFA measure of biomass was reflected by soil respiration, a measure of bacterial 

activity.  The results document the high quality 

of compost used in the study.   Based on the Ward Laboratory Haney Test Interpretation Guide 

the composted soil would be above average, 

and the untreated soil, below average. 


 Plant vigor: 

This was a qualitative assessment performed on June 5, three months after planting.  Two observers, 

experienced gardeners, assessed plant size, color, and foliage thickness and assigned a score to plants 

in the 7-plant block.  The highest ranked block was given a score of 100%, and the lowest, 25% (Table 3).   

The observers were blinded to treatment assignment. 


Table 3.  A qualitative assessment of plant vigor. 

Treatment assignment       Average score

Control (no amendments)


Algae, alone


Compost, alone


Algae + Compost



As noted, there was considerable plant loss during the disease, but the magnitude of loss was similar 

for the 4 treatment groups, so yield is reported as pounds of tomatoes per block and pounds per plant (Table 4).


Table 4.   Yield 

Treatment    / no.  plants                Pounds tomatoes/blockPounds/plant 

Control                      40



Algae, alone             36

8.0       (+10%*)

1.64    (+45%)

Compost, alone       37

15.28   (+110%)

3.2     (183%)

Algae + compost     36

15.48   (+113%)

3.7     (+227%)


*Compared with control 

The results are affected by two quirks of randomization.  First, two blocks in the compost alone 

group were outliers, producing 25 and 28 lbs tomatoes per block.  The next highest producing 

blocks yielded 20 and 22 lbs/block, both in the algae + compost group.   The two outlying 

blocks were adjacent to each other in one corner of the test garden; they were the only blocks

 in the test field that received 100% vigor scores (Table 3). That corner of the field appeared to be 

different than the rest.    


Secondly, the relatively small increase in yield per block was affected by the higher number of plants 

in the control group.  This was apparent when results were reported as pounds per plant.    



The initial soil testing indicated that the quality of compost used in the study was exceptional, 

so that compost treated sections of the test garden were more fertile.   This is reflected in the

results (Tables 3 and 4).   Both composted groups outperformed soil not receiving compost.  

Adding algae did not bring soil fertility to a comparable level. 

That said, when algae was added to poorer soil (Control), tomato yield per plant was increased 45%.  

Likewise, treating rich soil with algae boosted yield per plant by 16%.    

Thus,  algae boosted yield regardless of baseline fertility. 

Participation Summary

Educational & Outreach Activities

1 Consultations
2 Tours
1 Workshop field days

Participation Summary:

4 Farmers participated
1 Ag professionals participated
Education/outreach description:

Video_1 Video The results of the research will be published on the SSARE website, distributed on social media platforms, and shared with farmers' groups including but not limited to SAAFON,  BFAA, and the Farmer Veteran Coalition. The results of the research will be shared on multiple platforms and a variety of accessibility options to remove any barriers to access to the results. Sweetgrass Garden will create videos and photo graphic evidence as the project develops to document the progress and results from start to finish. The documentary will be shared as above and, if possible based on Covid-19 restrictions, at an on farm gathering of farmers and community members.

Learning Outcomes

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

Project Outcomes

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

The outcomes of this project show that the effects of Chlorella vulgaris ( liquid green algae concentrate) as a soil-amending bio-stimulant and foliar spray have positive implications for long-term soil health, healthy plants and yield, nutrient input cost reductions, and watershed safety. 

  1. Chlorella vulgaris concentrate increases soil microbial activity and respiration whether it is combined with nutrient inputs or not. Robust microbial activity and soil respiration are markers of soil health.
  2. C. vulgaris concentrate gives the soil’s biome what it needs in order to ensure the plant gets what it needs. We could say the algae is “farming the soil.” This focus on soil health is a basic principle of regenerative farming, a growing trend in agriculture for both commercial and academic sectors.
  3. Because C. vulgaris concentrate is a bio-stimulant and not a nutrient, its beneficial effect on the soil’s biome is not diminished by plant uptake. Regular applications of algae concentrate can provide long-term soil health.
  4. When combined with high-quality compost and adequate water, liquid C. vulgaris concentrate not only improves the soil activity, but boosts nutrient uptake, producing healthy plants and yield. Substituting a percentage of nutrient inputs with algae concentrate may be a viable way for fertilizer reduction. This could create both an economic and ecological advantage for farmers and their communities.
  5. C. vulgaris are single-cell green algae and are not water-permeable. The concentrate is diluted with water, delivering the cells to the soil in micro-amounts where they are lodged in the soil. Algae cells do not go into solution as would synthetic NPK nutrients. Therefore, there is no danger of runoff or watershed contamination when using C. vulgaris.
  6. C. vulgaris is commonly found in health food supplements and cosmetics. It is nontoxic and poses no threat to humans or animals. When used on pasture, it may be sprayed in direct proximity to cattle and horses.




We are continuing to study how various algae concentrations and application techniques work on different types of plants and growing situations. This is just one study, and it looks at the short-term effects of algae in combination with a high-quality, organic compost. We will continue additional studies to track long-term effects of C. vulgaris concentrate. We recommend that growers conduct trials on soil, crops, and pasture and then share findings to their growing communities, or perhaps engage state agricultural extensions to become involved in algae concentrate trials. Sweetgrass Garden welcomes questions about this project, and is happy to provide feedback assistance to others who wish to trial C. vulgaris concentrate. Contact us at: [email protected].

In closing, be aware that delays in the global supply chain along with material shortages have NPK input costs going steadily upward. The growing methods of the past 70 years are becoming increasingly untenable for today’s market. However, bio-stimulant alternatives such as algae concentrate are a viable solution. It is our hope to see current interest in regenerative/sustainable agriculture practices continue to expand so that both economic interests of the farmers and the ecological security of our land and water are addressed. Our goal is to provide growers with an economical, ecologically-sound alternative to synthetic fertility inputs. Algae concentrate can allow farmers to reduce synthetic NPK fertilizer usage by either supplementing a substantial percentage of nutrient inputs with algae concentrate or, when the soil is robust enough, replace synthetic NPK, altogether, with a paring of algae concentrate and organic carbon concentrate.

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.