Can controlled environment chambers be used for better seed-propagated strawberry transplants?

Paper referenced:

Tsuruyama, J., & Shibuya, T. (2018). Growth and flowering responses of seed-propagated strawberry seedlings to different photoperiods in controlled environment chambers. HortTechnology, 28(4), 453–458.


Although other crops are often in the spotlight when it comes to growing food in greenhouses, strawberry is gaining popularity and for good reason. It can be grown in greenhouses through the cold winter months in temperate climates to make local, fresh, high quality fruit available when not much else is. To maximize fruit set and profitability, starting the production cycle with high quality transplants is a necessity. Transplants, also known as plug or tray plants, can be produced from seed, rooted runner tips, or field dug bare root crowns, though, use of field dug plants can introduce pests and diseases into the greenhouse. Seed propagated hybrid strawberry cultivars suited for greenhouse production have been developed, leading to increased adoption of this technique in Europe and Japan.

Controlled environment technology presents strawberry plug producers with the tools needed to provide growers with high-quality transplants due to the tremendous level of control over environmental conditions such as light quality and quantity, humidity, and temperature. This high degree of control is advantageous because greenhouse grown plugs produced for August/September transplant can experience high temperatures and variable conditions, which can delay flowering and fruit production. However, with the use of an indoor controlled environment facility, plants can be grown under optimal conditions no matter the weather outside. In addition to temperature, photoperiod (the amount of time plants are exposed to light) as well as light intensity, can affect the growth and flowering of strawberries. Due to this, determining the optimal photoperiod for indoor plug production could lead to enhanced quality of transplants.

In this study the authors use two-seed propagated cultivars, one European (‘Elan’) and one Japanese (‘Yotsuboshi’), to produce tray plants for mid-August transplant. Both cultivars are long-day strawberry types which generally meaning flowering is promoted by long light periods.

To start the experiment, once seedlings had germinated and grown two true leaves, at 23 days old, they were replanted into larger trays for the light treatment phase. Next, groups of seedlings from both cultivars were subjected to different propagation systems. Four groups were grown in a growth chamber with blue/red LED lighting, this allowed the researchers to control the conditions the plants experienced, while the control group was grown in a greenhouse. The growth chambers were maintained at 25°C (77°F), but had different photoperiods and light intensities. The photoperiods tested in growth chambers were 8, 12, 16, and 24 hours. To ensure all plants received the same total amount of light, the light intensities were proportionally adjusted based on photoperiod, so the shortest photoperiod had the highest intensity and the longest had the lowest. The control plants were subjected to summer greenhouse conditions, moderated by shading during the day and air conditioning at night. The greenhouse average photoperiod was 13.6 hours with day temperatures around 30°C and night temperatures around 23°C for an average temperature of 26.8°C (80.2°F). All plants were grown in their respective treatment conditions for 38 days. After which, 10 plants per cultivar of each treatment were measured for dry mass, leaf area, leaf number, and length of the longest petiole to assess plant growth. Using pre- and post-treatment leaf area and dry mass, the relative growth rate (increase in mass), net assimilation rate (photosynthesis efficiency), and leaf area ratio were calculated.

After 38 days, when they had 6-7 leaves, plants were transplanted into a different greenhouse for the flower emergence trial, which lasted 110 days (from mid-August to late November). Plants were checked daily for flower bud emergence. Temperatures started high around 40°C (104°F) in August but slowly cooled as time progressed to a more typical strawberry production temperature range (25-10°C).

Results and Discussion
In both cultivars long-day, low intensity lighting out performed short-day and greenhouse conditions regarding plant mass, leaf area, petiole length, relative growth rate, and net assimilation rate, indicating enhanced photosynthetic efficiency. This suggests that plants were able to use the steady low amount of light over long periods more efficiently than high amounts of light over short periods or the summer greenhouse conditions, which exceeded the ideal growing temperatures for strawberry. Thus suggesting that using a controlled environment system with low intensity long-day lighting was more effective for plant growth than the greenhouse control.
Regarding how long it took plants to flower once transplanted into a fruit production greenhouse, for Elan, long-day conditions nearly halved time to flower compared to greenhouse control and short day photoperiods. This suggests that the long-day low intensity light treatments were effective for inducing flowers earlier than the summer greenhouse or short day conditions.
In Yotsuboshi however, photoperiod treatments did not have an effect on time to flower. Yet, the greenhouse control flowered slightly sooner than the photoperiod treatments, which may be due to transplant shock that the controlled environment plants experienced. These results demonstrate what other studies have found in that cultivars can react differently to the same conditions even if they are the same photoperiod type. Thus, these results suggest that more research is needed into which factors and their levels affect Yotsuboshi flowering to better understand the cultivar’s flower emergence.
Overall this study demonstrates that using low intensity LED lighting in controlled environment settings for long-day seed-propagated strawberry tray plants is a viable alternative to summer greenhouse production.

Effects of continuous or end-of-day far-red light on tomato plant growth, morphology, light absorption, and fruit production


Kalaitzoglou, P., W. van Ieperen, J. Harbinson, M. van der Meer, S. Martinakos, K. Weerheim, C.C.S. Nicole, and L.F.M. Marcelis. 2019. Effects of continuous or end-of-day far-red light on tomato plant growth, morphology, light absorption, and fruit production. Frontiers in Plant Science 10: 322


LEDs are becoming increasingly common in modern controlled environment horticultural systems. The potential energy-savings and flexibility of LEDs makes them attractive lighting options compared to traditional high-pressure sodium or metal halide bulbs. Questions remain regarding the effects of light wavelengths emitted by LEDs on plant growth. Plants respond to differing wavelengths of light by changing physical characteristics and growth. Shading causes a low red light (R) to far-red light (FR) ratio (R:FR), resulting in low levels of the active form of a key plant photoreceptor, phytochrome. This low phytochrome stationary state (PSS) leads to a variety of shade avoidance responses that affect plant morphology and development. In contrast, LEDs used for greenhouse lighting often emit low levels or zero far-red light, causing plants to have higher PSS values than sunlight. Little is known about the effects of changing R:FR ratios on photosynthesis and plant growth in greenhouses using LEDs. Using tomato as a model crop, researchers at Wageningen University investigated how tomato morphology changes in response to higher than sunlight R:FR ratio supplied by LEDs and what effect these changes have on plant light absorption and growth (Kalaitzoglou et al., 2019). In addition, the researchers were interested if a short end-of-day FR treatment (EOD-FR) could compensate for any negative effects of growing plants without FR light during daytime.


The researchers conducted two experiments (EXP1 & EXP2). In both experiments, greenhouse chambers were divided into 15 equal compartments, each containing 20 tomato plants. Each compartment was illuminated by a combination of red (95%) and blue (5%) LEDs that supplied approximately 150 mmol
m-2 s-1 of photosynthetically active radiation (PAR) over the course of a 16 hour day. Additional FR LEDs were installed to provide five different treatments based on FR intensities. In four treatments, both FR LEDs and red/blue LEDs were on at the same time during the day, resulting in plant PSS values of 0.70, 0.73, 0.80, 0.88. The fifth treatment was a 15 minute end of day FR cycle (EOD-FR) following the end of the photoperiod. To investigate the interaction between the effects of FR and solar radiation on plant morphology the first experiment (EXP1) used a blackout screen to block incoming sunlight, while the second experiment (EXP2) exposed the plants to broadband solar radiation from morning to afternoon. In addition, EXP1 lasted only four weeks after transplanting while EXP2 was extended to 16 weeks to allow for tomato fruit development.

In both experiments, researchers measured plant growth and morphology traits such as plant height, petiole angle, and leaf area. In EXP2, fruit traits including total fruit weight (g/plant), number of fruits, and number of open flowers at 4 weeks were recorded. Additional measured traits included leaf ligh absorbance and chlorophyll and carotenoid content. To simulate light absorption for each treatment, researchers constructed a 3D plant model using GroIMP software (Hemmerling et al., 2008). Researchers used the model to estimate the effects of changes in plant morphology in response to FR light treatments on plant light absorption.

Supplemental Figure S5. (Kalaitzoglou et al., 2019)


Increasing R:FR ratio to levels above sunlight had a negative impact on tomato plant growth. In both experiments, morphological parameters such as plant height and leaf area decreased as PSS values became higher (Supplemental Figure S5). The researchers concluded that lower levels of plant light absorption in high PSS treatments were primarily caused by the decrease in leaf area, ultimately reducing plant growth. Similar results were observed for fruit characteristics in which fruit size and fruit number were greater in treatments with increasing FR compared to the 0.88 PSS treatment (no FR) and EOD-FR treatment. FR treatments also stimulated early flower and fruit maturity. Interestingly, while leaf PAR absorbance and chlorophyll content were lower in low PSS treatments, net photosynthesis was higher. Researchers attributed this result to the Emerson effect in which a higher rate of photosynthesis occurs when plants are exposed to a simultaneous mixture of red and far-red light. In both studies, EOD-FR treatments were not enough to offset the negative effects of growing plants with low levels or zero FR light throughout the day. In conclusion, the results of the study indicated that the presence of FR light increased fruit yield and accelerated flowering and FR LEDs could be a beneficial addition to greenhouses to improve tomato fruit production.

Energy, water and nutrient impacts of California-grown vegetables compared to controlled environmental agriculture systems in Atlanta, GA

Energy, water and nutrient impacts of California-grown vegetables compared to controlled environmental agriculture systems in Atlanta, GA

Steven W. Van Ginkel, Thomas Igou, Yongsheng Chen*School of Civil and Environmental Engineering, Georgia Institute of Technology, 200 Bobby Dodd Way, Atlanta, GA 30332, United States.


Van Ginkel, S.W., T. Igou, and Y. Chen. 2017. Energy, water and nutrient impacts of California-grown vegetables compared to controlled environmental agriculture systems in Atlanta, GA. Resources, Conservation and Recycling 122:319-325. Https:// (Links to an external site.)


This paper compares the efficiency of California Based traditional vegetable agriculture to hydroponics and aquaponics systems. Efficiency is defined by water usage, energy and nutrient input as it relates to crop yield. California is the leader in fruit and vegetable agriculture; therefore the rest of the United States is reliant on their system. However, California is also susceptible to severe drought, which can lead to reduce yields. Additionally, California has very large watershed, which can cause runoff of fertilizers in ponds, lakes and other bodies of water. Therefore to mitigate the environmental footprint of agriculture production, the author’s suggests that future generations focus on urban agriculture. Aquaponics is a system that allows the production of vegetables and fish, while reducing the input of fertilizers, and using waste byproducts as the source of nutrients. The authors show that this system reduces the nutrient input, water usage and is more productive that traditional based vegetable production. Therefore the purpose of this paper is to compare and contrast the productivity of each system.

 Experimental Design

California vegetable data was derived from Data was taken for several crops including tomato, spinach, strawberries, peppers, and broccoli. The data displays yield, nutrient input, energy input for each crop. The data was normalized by dividing each component by yield per acre. For hydroponics, there was one grower who grew lettuce and leafy greens in shipping containers. The data was normalized for energy (lighting and cooling) and water usages over a year divided by yield per container. For aquaponics, there were three growers, one from Hawaii and two from University of Virgin Islands and Atlanta, GA. All growers used deep-water culture and grew leafy greens. The data was normalized for energy and water utilized over a year divided by the yearly productivity. Data from all three systems was then compared using statistical analysis.


Areal Productivity

When comparing hydroponics and aquaponics there was no significant difference in the areal productivity. However, there was a significant difference between the ponic-systems and the California-based system. Ponic-systems were found to be 10 to 29 times more productive than the California-based system. In addition, areal productivity in hydroponics could be substantially improved increasing vertical production in closed environments.

Energy Usage

Hydroponics uses 30 times more energy (lighting, cooling) than the California-based system. There was no significant difference in energy usage between aquaponics and California-based system. However there were differences in energy usage between aquaponic growers, therefore it is would be wise to compare each aquaponic grower to the California-based system in the future.

 Water Usage

California-system uses 66 and 8 times more water than hydroponics and aquaponics. There were differences in water usage between hydroponics and aquaponics, however the authors suggests that results maybe skewed due to the lack of data points.


Based on the authors study, it seems that ponic-systems are overall more efficient than California-based system. They believe that these systems should be integrated into urban cities. By integrating such systems, cities become less reliant on vegetable and fruit production from California. At the same time it reduces the negative environmental footprint. Nevertheless, the biggest challenge will be to address the socio-economic challenges in integrating the system into urban environments.