An integrated approach to developing a day neutral strawberry production industry

2007 Annual Report for LNE06-241

Project Type: Research and Education
Funds awarded in 2006: $88,700.00
Projected End Date: 12/31/2010
Region: Northeast
State: Maryland
Project Leader:
Willie Lantz
University of Maryland Extension

An integrated approach to developing a day neutral strawberry production industry


Strawberry producers in the eastern United States primarily use spring bearing cultivars, which produce a crop for a relatively short period of time. Harvest is finished by the end of June; however, with large urban populations nearby, the demand for fresh strawberries is strong throughout the summer. Until recently the small size and poor quality of day neutral strawberry cultivars have prohibited day neutral strawberry production from filling a portion of this market. Many growers are looking for ways to produce fruit during the summer months to meet the demand by the consumers.

This project will introduce farmers to new varieties of day neutral strawberries, which have the potential to produce heavy yields of fruit with very desirable flavors. Potential producers will be invited to yearly field days, have the opportunity to attend a strawberry short course, and participate in monthly field walks during the growing season.

As a result of this project, growers will have information on the best nitrogen fertilization levels, plant propagation methods, growing techniques and variety selection. During the first year of the project organic nitrogen (compost) and nitrogen levels will be evaluated to determine which level will produce the highest marketable yields and healthiest plants. In the second year of the project, growers will evaluate the best method of propagating day neutral strawberry plants. In the final year of the project, growers will evaluate new varieties in variety trial plots.

Potential producers will be invited to attend annual field days held during each of the three years of the project. Of the 200 potential producers that will attend a field day, 100 will attend a strawberry short course or field walk to further their knowledge of growing day neutral strawberries and 20 will plant day neutral strawberries utilizing new varieties and production techniques. Surveys will be conducted to determine that milestones have been reached.

Objectives/Performance Targets

The primary outcome of this project will be to establish a day neutral strawberry production system in the cool climate areas of the northeast. Information gained through this project will be presented through field days, yearly strawberry short courses, and field walks held during the growing season. 200 farmers will attend field days on growing day neutral strawberries. Farmers who have interest in producing fruit will be invited to attend a yearly strawberry short course or field walks. 100 farmers will attend a second educational event such as a strawberry short course or field walk. Of the farmers that attend the field walks or strawberry short courses, 20 will add day neutral strawberries growing new varieties utilizing advanced growing techniques to their farming operation. All participants of the short courses and field days will be surveyed to determine who has added day neutral strawberries to their farming enterprises.


During 2007, the project completed three separate research projects. The first project was conducted at Penn State’s Horticulture Farm at Rock Springs, PA. The first year everbearer field was carried over to determine the effect of the nutrient treatments on a second year planting. The research also provided information about yield on second year day neutral strawberry plantings. The second part of the research was conducted on two farms in Garrett County, Maryland. This experiment compared fall planting versus spring plantings. Two types of fall plants were established, plugs and fresh dug plants, and two types of spring plants, plugs and bare root dormant plants were compared. One location was inside a high tunnel. The third part of 2007 research project investigated the effect of removing flower blossoms after planting spring plug plants. This tested whether the general recommendation to remove the flower blossoms for one to four weeks after planting helped the plants grow more vigorously before starting fruit production and resulted in larger fruit size. Removing flower blossoms is a labor intensive activity. This research was carried out on two cooperating farms in Garrett County.

The experiment on compost rates and liquid nitrogen fertigation
in a 2nd yr field at Penn State

Treatments consisted of compost at rates to provide 0, 400, and 800 lb of total N/acre (0, 40, and 80 lb of N/acre/year assuming a 10% mineralization rate) and 0, 1 and 2 lb of N/week/acre as 20-10-20 inorganic soluble fertilizer with micronutrients. Compost was applied in 2006 at planting. In 2007, fertigation treatments were applied once per week from May 22 through October 9.

Fruit production and harvest occurred in three relatively distinct flushes, the first occurring from May 23 to July 6, the second from July 20 to Aug. 31, and the third from Sept. 7 to Oct. 27. Yield data were analyzed separately within the three flushes to detect whether there were changes in the plants’ nutrient needs as the year progressed, and were also analyzed as totals for the year.

The early and mid-summer harvests were the largest, averaging 9985 and 9185 lb/acre in total yields across all treatments. The fall harvest was the smallest, averaging 6651 lb/a. During the first harvest flush, the only significant difference among treatments was that when the inorganic fertilizer rate of 1 lb N/acre/week was applied, the highest compost rate resulted in the highest yields. During the second harvest flush, if no compost was applied, both rates of fertigated N resulted in higher yields compared to no fertigated N. There were no significant differences among treatments within the third harvest flush.

There were no relative changes in treatment effects through the year, therefore the flush-specific effects were also found in treatment differences for total annual yield. In total yields for the season, when no compost was applied, applying either soluble fertilizer rate resulted in higher marketable, unmarketable, and total yields than if no N were fertigated. If compost at either the 400 lb or 800 lb total N/a rate were applied, there was no significant difference in marketable, unmarketable, or total yields among nitrogen fertigation rates, though yields numerically tended to be highest at the 1 lb N/acre/day rate. There was no yield improvement obtained by increasing the N to 2 lb N/a/week fertigation rate, whether compost was applied or not.

The highest compost application rate either produced or to tended to produce higher marketable, unmarketable, and total yields than either applying no compost or the lower amount of compost. Whether this yield increase is due strictly to nitrogen, other nutrients, or improvements in such factors as soil structure, aeration, or water infiltration is not known. The soil at this site is heavy with a large clay component. It appeared that the percentage yield increases that resulted from applying compost were greatest (25%) when no inorganic fertilizer was applied, even though the statistical significance was lower. This could indicate that was greater variability among individual plot performance when no compost was applied.

Percentage marketable fruit and mean berry weight was not significantly different among any of the treatments. Mean berry size was smaller in 2007 than in 2006, presumably due to a large number of branch crowns on the two year old plants.

Table 1
Inorganic N 0 lb/a/week 1 lb/a/week 2 lb/a/week p(F) inorg. N*

Marketable Yield (lb/a)

None 14,292 B** 17,944 b A 17,822 a A 0.002
400 lb total N 16,971 17,920 b 16,174 b 0.55
800 lb total N 18,717 19,192 a 18,202 a 0.77
p(F) compost* 0.23 0.01 0.006

Unmarketable Yield (lb/a)
None 7,898b B 9,453 A 9,947 A 0.02
400 lb total N 9,120ab 10,252 10,363 0.39
800 lb total N 9,895a 11,269 11,222 0.35
p(F) compost 0.04 0.14 0.14

Total Yield (lb/a)
None 22,838 B 27,397b A 27,769b A 0.001
400 lb total N 26,092 28,172b 26,537c 0.65
800 lb total N 28,612 30,461a 29,425a 0.61
p(F) compost 0.11 0.03 0.006

Marketable Fruit (%)
None 64.9 64.9 63.5 0.63
400 lb total N 63.7 62.9 60.1 0.25
800 lb total N 64.0 62.1 61.2 0.54
p(F) compost 0.93 0.22 0.27

Mean Berry Weight (g)
None 9.4 9.6 9.9 0.16
400 lb total N 9.6 9.8 9.5 0.46
800 lb total N 9.6 9.9 9.9 0.37
p(F) compost 0.77 0.25 0.39
*p(F) inorg. N indicates the probability of means of inorganic N fertigation treatments being different from each other within each compost treatment. p(F) compost indicates the probability of compost treatments being different from each other within each inorganic N treatment.
**Means were separated using Fisher’s Protected LSD test. Means followed by different letters are significantly different at the 0.05 probability level. Lower case letters are used to denote differences among fertigated inorganic N levels. Upper case letters are used to denote differences among compost treatments.

Summary: The bottom line is that high yields could be obtained by applying the highest rate of compost alone with no need for additional inorganic nitrogen. If no compost is applied, an inorganic nitrogen rate of 1 lb of N/acre/week is sufficient to produce high yields. Both compost and inorganic N at 1 lb of N/acre/week may be applied for maximum yields, but the increases in yield relative to applying either N source alone are not likely to be economically significant. An economic analysis is underway to determine the most economical methods of producing the highest yields.

Planting Time and Propagation Method for Variety: ‘Evie 3’

Fall plug plants and fresh dug day neutral strawberries were planted in mid September 2006. Spring planted plugs and dormant bare root plants were planted the first week of May 2007. The plants were planted in two 20 plant blocks on raised beds covered with plastic mulch.

Fall planted plants established well and were protected through the winter with heavy floating row covers in the outside planting. Fall planted plants planted outside started to fruit on May 29th as compared to spring planted plants which began on July 4th. At the high tunnel site, blossoms were removed on the fall planted plants until the spring plants were planted.

In Table 2 below, the yield difference between the four types of nursery stock were not significantly different in the tunnel planting; however, fall plants did out produce the spring plantings in yield (weight/plant). Outdoors, the fall plug plants significantly out performed the fall dug plants. Both types of fall plants out performed the spring planted plants by a wide margin. The fruit size on the spring dug (dormant) plants was also significantly less than the other planting methods.

Table 2 – Plant Timing/Type Experiments
Site 1 – High Tunnel Site 2 – Outside
Wt/plant(g) Berry Wt.(g) Wt/plant
Mean Berry Wt. (g)

Fall dug 667 10.0 176b 10.0a
Fall plug 551 8.2 274a 11.3a
Spring dug 177 8.7 23c 5.7b
Spring plug 333 9.6 63c 11.7a

p(F) 0.0648 0.46 0.0037 0.008

These results indicate that planting fall plug plants should be a more productive method of growing day neutral strawberries. However, fall plantings will require more labor to protect plants from winter injury. Early spring yield may not happen each year due to late frosts. In the high mountains of the east, water for overhead irrigation for frost protection is difficult to obtain. Protection with floating row covers is feasible, but this also increases the costs of production.

At this time, fall plug plants are also not commercially available. A local grower will be establishing a nursery for fall plug production during the 2008 growing season. The cost for the fall plugs is unknown at this time but is not expected to excess that of spring plugs (about $.33 per plant). Early spring production from fall planted plants may also not provide as high a return on fruit production as it will be competing with June bearing plants and price will be depressed.

Summary: From 2007 data, fall planted plugs will provide the highest yield potential for producers but may not provide the highest profit margin. Additional research needs to be conducted to determine the cost of production and anticipated returns on fruit production on fall versus spring plantings. The experiment also needs to be repeated at more locations and using different varieties. Yield on spring planted plants at both locations were much lower than other spring planted locations. In 2008, we will continue to compare fall planted plugs and spring planted plugs. These data will help add confidence to our recommendations.

Flower Blossom Removal

In this research, ‘Seascape’ day neutral strawberry plants were planted the middle of May 2007. The plants were planted on raised beds covered with plastic mulch. Two parallel rows were planted on the top of a 30” wide bed with 6’ from the center of one bed to the center of the other bed. The plug plants were planted 12” apart in each row. After planting, three groups of 20 plants were randomly selected from each of three rows. Blossoms were removed up to three different dates after planting.

Fruit production for the various treatments began on:
Treatment #1= remove blossoms until June 1st – fruit ripe July 2nd,
Treatment #2= remove blossoms until June 14th – fruit ripe July 10th,
Treatment #3= remove blossoms until July 2nd – fruit ripe July 17th.
While the treatments did have an affect on when plants started to fruit; treatments had no effect on total annual fruit production (weight/plant). The only significant difference found was that of mean berry weight at site 101. At this site, the mean berry weight was significantly lower for treatment #3. This result seems to be random and is contrary to that experienced in other everbearing regions.

Table 3 – Blossom Removal Experiments
Site 101 Site 102 Combined*
Wt per plant
(g) Mean Berry Wt. (g) Wt per plant
(g) Mean Berry Wt. (g) Wt per plant
(g) Mean Berry Wt. (g)

#1 Removed until June 1 835 9.0a 413 10.5 624 9.8
#2 Removed until June 14 845 8.7a 440 9.7 642 9.2
#3 Removed until July 2 815 8.3b 481 11.1 648 9.7

p(F) 0.79 0.0162 0.29 0.28 0.68 0.33

Site 101 832a 10.4a
Site 102 445b 8.7b

p(F) <0.0001 0.0439
• Site by blossom removal treatment interaction not significant, so sites can be combined (interaction sig. at p(F) = 0.32 for wt per plant, and 0.089 for mean berry wt, respectively).

Summary: producers need not remove flowers after the plug plants are planted in Spring. This will represent a savings in the labor required to establish spring planted day neutral strawberry plants. The only advantage to flower removal would be to delay fruit production to target a certain market. This research demonstrates that removing the flowers neither hurts or helps overall production; however, it should be noted that flowers were removed when plants were in the plugs at the nursery. We continue to recommend flower removal at the nursery.

Data from the 2006 project was also presented at the 2007 Northeast Region American Society for Horticultural Science meeting, the 2007 Mid Atlantic Fruit and Vegetable Conference, and the 2007 Western Maryland Regional Fruit Meeting. A Day Neutral Strawberry Twilight meeting was held in Garrett County at one of the cooperating farms. The principal investigators also conducted a 6 hour Strawberry Production Short Course that was attended by 16 producers. Willie Lantz also presented a talk on growing day neutral strawberries at the 2007 Rural Enterprise Conference held in Kingwood, WV. A total of 145 potential producers attended the various presentations made about the day neutral strawberry project.

Impacts and Contributions/Outcomes

To assist those interested in growing day neutral strawberries, the Garrett County Extension office worked with a local greenhouse to prepare and grow plug plants for spring planting. 13 farms planted over 20,000 day neutral strawberry plants in 2007. This resulted in new producers with nearly one acre of annual planted day neutral strawberries.
An end of season survey was sent to individuals that produced day neutral strawberries. Of the producers that responded, 100% indicated that they planned to produce day neutral strawberries in 2008. 85% indicated that they intended to keep production the same or increase production. Six producers responded to the question asking them to report gross income from strawberry production. These six farms reported gross income of $16,639.00 from 11,400 plants. The extension office is coordinating plant purchases for the spring of 2008. To date 15 producers have ordered 25,000 plants for 2008.


Harry Swartz

[email protected]
Associate Professor - Small Fruits
Univeristy of Maryland
2102 Plant Science Building
Univerity of Maryland
College Park, MD 20742-4452
Office Phone: 3014054337
Kathleen Demchak

[email protected]
Small Fruit Specialist
Penn State University
107A Tyson Building
University Park, PA 16802
Office Phone: 8148632303