Methods for growing strawberries

Abstract

A method for growing strawberries indoors comprises exposing strawberry plants to a pulsed light source. The light source may be configured to switch off and on at regular time intervals, the duration of the on / off cycles may be about 1 second. The light source may be off between about 10% and about 40% of each cycle. The light source may emit light which mimics sunlight. The intensity of the light source may be varied throughout each 24-hour period to mimic the outdoor light levels of a summer day and night. The strawberry plants may be an everbearing variety. Also described are one or more strawberries produced by the method, an apparatus 1 for growing strawberry plants and a building or structure for growing strawberry plants.

Description

The present invention relates to methods for growing strawberries, in particular to methods for growing strawberries indoors. Strawberries are a small but economically important group of plants of the genus Fragaria. The garden strawberry is a hybrid species of the genus known as Fragaria x ananassa. In the UK, soft fruits, principally strawberries, were historically grown and consumed in midsummer and the production was predominantly from home produced strawberries, with limited imports. In 1988, the UK supply of strawberries stood at 63.5 thousand tonnes, with 28% imported. By 2019, strawberry consumption had increased to 196.7 thousand tonnes, up 210% from 1988, of which 72% were grown in the UK, 30% was imported and 2% exported. Seasonality of the crop is a limiting factor for outdoor strawberry production, especially in countries such as the UK. The season peak can vary from two months (June-July) to six months (May to October) depending on the cultivars and the use of protection. UK home production is limited for the months April, November and December, while there is no production at all available from January to March. It would, therefore, be desirable to grow strawberries indoors to provide harvest at any time of the year, irrespective of the outside growing conditions. However, whilst this has been attempted, successes have been variable and the process is often energy intensive with large amounts of electricity for lighting required. There is, therefore, both a financial and environmental cost associated with current attempts. Whilst this has been improved to some extent with the advent of LED lighting and solar power, there is still a need to reduce energy consumption for growing strawberries indoors, especially in climates which suffer from poor levels of light during the winter months. One possible way to reduce power consumption is to use pulsed light instead of continuous light for growing crops. However, whilst previous work conducted in lettuces produced results for leaf weight similar to those for continuous light using pulsed LEDs with a frequency of 1 kHz, the resultant leaf weight was still lower using pulsed light compared to continuous light (Son et al (2016), Hortic. Environ. Biotechnol. 57(6):560-572). Whilst another study showed an increase in fresh and dry weight of lettuces using pulsed light at a frequency of 0.5 kHz compared to continuous light (Miliauskiene et al (2021) Plants, 10, 762), it is difficult to extrapolate this to strawberry plants because strawberry plants have different growth characteristics compared to lettuces, most notably due to production of berries rather than leaves, and different shaped and sized leaves. In addition, if the same effect on leaf mass was seen in strawberry plants, there is every chance that this could result in lower levels of berry production due to the energy of the plant being focussed on leaf production rather than berry production. It is, therefore, an object of the present invention to seek to alleviate the above identified problems. SUMMARY OF THE INVENTION According to one aspect of the present invention, there is provided a method for growing strawberries indoors, wherein the method comprises exposing strawberry plants to a pulsed light source. Preferably, the light source is configured to repeatedly switch off and on at regular time intervals in a continuous series of off / on cycles. Preferably, the duration of each off / on cycle is between about 0.5 seconds and about 10 seconds, preferably between about 0.5 seconds and about 5 seconds, preferably between about 0.5 seconds and about 3 seconds, preferably between about 0.5 seconds and about 2 seconds, preferably between about 0.5 seconds and about 1.5 seconds, preferably between about 0.8 seconds and about 1.2 seconds, preferably about 1 second. Preferably, the frequency of the off / on cycles is between about 2Hz and about 0.1Hz, preferably between about 2Hz and about 0.2Hz, preferably between about 2Hz and about 0.33Hz, preferably between about 2Hz and about 0.5Hz, preferably between about 2Hz and about 0.66Hz, preferably between about 1.25Hz and about 0.83Hz, preferably about 1Hz. Preferably, within each off / on cycle, the light source is off for between about 10% and about 40% of each cycle, preferably for between about 20% and about 30%, most preferably for about 25% of each cycle. Preferably, the light source is configured to repeatedly switch off for between about 100 milliseconds and about 400 milliseconds and on for between about 600 milliseconds and about 900 milliseconds. Preferably, the light source is configured to repeatedly switch off for between about 200 milliseconds and about 300 milliseconds and on for between about 700 milliseconds and about 800 milliseconds. Preferably, the light source is configured to repeatedly switch off for about 250 milliseconds and on for about 750 milliseconds. Preferably, the light source is a light-emitting diode (LED). Preferably, the light source emits light at wavelengths which mimic sunlight. Preferably, the light source emits blue, green, red and far red light. Preferably, the light source emits a spectrum of light from a wavelength of about 280nm to a wavelength of about 800nm, preferably from a wavelength of about 350nm to a wavelength of about 800nm, preferably from a wavelength of about 400nm to a wavelength about 750nm. Preferably, the strawberry plants are an everbearing variety. An ’’everbearing” variety is a variety which produces crops multiple times during the growing season. Everbearing varieties are also known as perpetual varieties. Preferably, the strawberry plants are Fragaria x ananassa strawberry plants. Preferably, the strawberry plants are Fragaria x ananassa Favori strawberry plants. Preferably, the intensity of the light source is varied throughout each 24-hour period to mimic the outdoor light levels of a summer day and night. Preferably, the intensity of the light source is varied between about 100% intensity and about 0% intensity during each 24-hour period. Preferably, when the light source is at 100% intensity, the plants receive between about 15 mols / m2 / day and about 30 mols / m2 / day of light, preferably between about 20 mols / m2 / day and about 30 mols / m2 / day of light, preferably about 25 mols / m2 / day of light. Preferably, the intensity of the light source is about 100% intensity for at least about 10 hours per 24-hour period, preferably for at least about 10.5 hours per 24-hour period, preferably for about 10.5 hours per 24-hour period. Preferably, the intensity of the light source is about 0% intensity for at least about 9 hours per 24-hour period, preferably for at least about 19.5 hours per 24-hour period, preferably for about 9.5 hours per 24-hour period. Preferably, the temperature is varied throughout each 24-hour period to mimic the outdoor temperature of a summer day and night. Preferably, the temperature is varied between about 12°C and about 24°C, preferably between about 14°C and about 22°C during each 24-hour period. Preferably, the temperature is between about 20°C and about 24°C, preferably about 22°C for at least about 4 hours per 24-hour period, preferably for at least about 4.5 hours per 24-hour period, preferably for about 4.5 hours per 24-hour period. Preferably, the temperature is between about 12°C and about 16°C, preferably about 14°C for at least about 9 hours per 24-hour period, preferably for at least about 9.5 hours per 24-hour period, preferably for about 9.5 hours per 24-hour period. Preferably, the relative humidity is varied between about 60% and about 95%, preferably between about 70% and about 90% during each 24-hour period. Preferably, the relative humidity is between about 60% and about 80%, preferably about 70% for at least about 9.5 hours per 24-hour period, preferably for at least about 10 hours per 24-hour period, preferably for about 10 hours per 24-hour period. Preferably, the relative humidity is between about 80% and about 95%, preferably about 90% for at least about 9 hours per 24-hour period, preferably for at least about 9.5 hours per 24-hour period, preferably for about 9.5 hours per 24-hour period. Preferably a light intensity of about 0% intensity, a temperature of between about 12°C and about 16°C, preferably about 14°C, and relative humidity of between about 80% and about 95%, preferably about 90%, mimics night-time conditions. Preferably a light intensity of about 100% intensity, a temperature of between about 16°C and about 24°C, preferably between about 16°C and about 22°C, preferably about 22°C, and relative humidity of about 60% and about 80%, preferably about 70% mimics day-time conditions. Preferably, the method comprises growing the strawberry plants at least until the plants produce ripe strawberries. Preferably, the method comprises harvesting strawberries from the plants. Preferably, the method is performed indoors. Preferably, “indoors” means in an environment in which the plants receive a reduced level of natural sunlight compared to being grown outdoors, preferably in which the plants receive no natural sunlight. Preferably, “indoors” means inside a building or structure in which the plants are shielded from natural sunlight. According to another aspect of the present invention, there is provided a one or more strawberries produced by a method as described herein. In another aspect of the present invention, there is provided an apparatus for growing strawberry plants, wherein the apparatus comprises (i) a support for supporting one or more strawberry plants, (ii) a light source for illuminating the strawberry plants, and (iii) a controller for controlling the light source, wherein the controller is programmed to repeatedly switch the light source off and on at regular time intervals in a continuous series of off / on cycles. According to another aspect of the present invention, there is provided a building or structure for growing strawberry plants, wherein the building or structure comprises one or more apparatus as described herein. Within this specification embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein and vice versa. For example, it will be appreciated that all preferred features of the light source of the method are applicable to the light source of the apparatus. Within this specification, the term “about” means plus or minus 20%, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2%. It will also be appreciated that the disclosure extends to passages herein which refer to the term “about” but with said term removed. Preferably, about 0% means below 0.2%, preferably below 0.1%, preferably below 0.05%, preferably below 0.02%. It will be appreciated that reference to “one or more” includes reference to “a plurality”. The genetic origin of the Fragaria x ananassa strawberry plant is believed to be France. DETAILED DESCRIPTION Example embodiments of the present invention will now be described with reference to the accompanying Figures, in which: Figure 1 shows an apparatus as described herein; and Figure 2 shows a building as described herein. The present invention relates to methods for growing strawberries indoors. An experiment was performed using pulsed light to grow strawberry plants where the light was repeatedly turned off for 250 milliseconds and then on for 750 milliseconds. Favori strawberry plants were grown indoors under LED lights which emitted blue, green, red and far red across a wavelength range of 400nm to 750nm. The strawberry plants were obtained from a wholesale nursery in the Netherlands. The plants were grown in coir bags in racks under LED lights and were kept well-watered throughout the trial. Bees were used to pollinate the flowers. Each day, temperature, light level and relative humidity were controlled to mimic the outdoor situation of a summer day / night. The levels used are shown in Table 1 below. Table 1 - Temperature, light level and relative humidity values Time Stamp Light Intensity State Temperature Relative Humidity 00:00 0% Night 14°C 90% 00:30 0% Night 14°C 90% 01:00 0% Night 14°C 90% 01:30 0% Night 14°C 90% 02:00 0% Night 14°C 90% 02:30 0% Night 14°C 90% 03:00 0% Night 14°C 90% 03:30 0% Night 14°C 90% 04:00 0% Night 14°C 90% 04:30 0% Night 14°C 90% 05:00 0% Night 14°C 90% 05:30 0% Night 14°C 90% 06:00 0% Night 14°C 90% 06:30 0% Night 14°C 90% 07:00 0% Night 14°C 90% 07:30 0% Night 14°C 90% 08:00 0% Night 14°C 90% 08:30 0% Night 14°C 90% 09:00 30% Morning 14°C 80% 09:30 70% Morning 15°C 77% 10:00 85% Morning 16°C 73% 10:30 100% Day 17°C 70% 11:00 100% Day 18°C 70% 11:30 100% Day 19°C 70% 12:00 100% Day 20°C 70% 12:30 100% Day 20°C 70% 13:00 100% Day 22°C 70% 13:30 100% Day 22°C 70% 14:00 100% Day 22°C 70% 14:30 100% Day 22°C 70% 15:00 100% Day 22°C 70% 15:30 100% Day 22°C 70% 16:00 100% Day 22°C 70% 16:30 100% Day 22°C 70% 17:00 100% Day 22°C 70% 17:30 100% Day 22°C 70% 18:00 100% Day 19.5°C 70% 18:30 100% Day 19°C 70% 19:00 100% Day 18.5°C 70% 19:30 100% Day 18°C 70% 20:00 100% Day 17.5°C 70% 20:30 100% Day 17°C 70% 21:00 100% Day 16°C 73% 21:30 85% Evening 15°C 77% 22:00 70% Evening 14°C 80% 22:30 30% Evening 14°C 85% 23:00 0% Night 14°C 90% 23:30 0% Night 14°C 90% A light intensity of 100% provided 25 mols / m2 / day of light to the plants. As will be appreciated, the plants receiving non-pulsed light were provided with this amount of light continuously during the 100% intensity time periods, whereas the plants receiving pulsed light were provided with this amount of light only during the “on” periods of 750 milliseconds during the 100% intensity time periods. As will also be appreciated, for those periods in which the light intensity was less than 100%, the amount of light received by the plants was reduced accordingly. As such, at a light intensity of 50%, the plants received 12.5 mols / m2 / day of light. The pulsed-light plants received pulsed-light at all times during those time periods that light was provided to the plants. The results from Example 1 are shown in Table 2 below. Table 2 - Cumulative Yield per Plant of Ripe Berries (g) Days since planting Non-Pulsed Plants (Cumulative Yield) Pulsed Plants (Cumulative Yield) 120 260g 230g 125 270g 300g 130 280g 370g 135 300g 420g Remarkably, as will be seen, despite the pulsed-light plants receiving 25% less light compared to the non-pulsed light plants, the amount of fruit produced was far greater for the pulsed plants. An apparatus 1 for growing strawberries is shown in Figure 1. The apparatus 1 includes a support 2 for supporting one or more strawberry plants (not shown) and an array of LEDs 3 for illuminating strawberry plants. A controller 4 controls the light source and is programmed to repeatedly switch the light source off and on at regular time intervals in a continuous series of off / on cycles. A side view of a building 5 which houses a plurality of the apparatus 1 is shown in Figure 2. It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications are covered by the appended claims. 11 The content of all references cited herein are incorporated herein by reference in their entirety.

Claims

1. A method for growing strawberries indoors, wherein the method comprises exposing strawberry plants to a pulsed light source.

2. A method according to claim 1, wherein the light source is configured to repeatedly switch off and on at regular time intervals in a continuous series of off / on cycles.

3. A method according to claim 2, wherein the duration of each off / on cycle is between about 0.5 seconds and about 10 seconds.

4. A method according to claim 2 or 3, wherein the duration of each off / on cycle is about 1 second.

5. A method according to any of claims 2 to 4, wherein within each off / on cycle, the light source is off for between about 10% and about 40% of each cycle.

6. A method according to any of claims 2 to 5, wherein within each off / on cycle, the light source is off for about 25% of each cycle.

7. A method according to any preceding claim, wherein the light source is a lightemitting diode (LED).

8. A method according to any preceding claim, wherein the light source emits light at wavelengths which mimic sunlight.

9. A method according to any preceding claim, wherein the light source emits blue, green, red and far red light.

10. A method according to any preceding claim, wherein the light source emits a spectrum of light from a wavelength of about 280nm to a wavelength of about 800nm.

11. A method according to any preceding claim, wherein the strawberry plants are an everbearing variety.

12. A method according to any preceding claim, wherein the strawberry plants are Fragaria x ananassa strawberry plants, preferably Fragaria x ananassa Favori strawberry plants.

13. A method according to any preceding claim, wherein the intensity of the light source is varied throughout each 24-hour period to mimic the outdoor light levels of a summer day and night.

14. A method according to any preceding claim, wherein the method comprises growing the strawberry plants at least until the plants produce ripe strawberries.

15. A method according to any preceding claim, wherein the method comprises harvesting strawberries from the plants.

16. One or more strawberries produced by a method according to any preceding claim.

17. An apparatus for growing strawberry plants, wherein the apparatus comprises (i) a support for supporting one or more strawberry plants, (ii) a light source for illuminating the strawberry plants, and (iii) a controller for controlling the light source, wherein the controller is programmed to repeatedly switch the light source off and on at regular time intervals in a continuous series of off / on cycles.

18. An apparatus according to claim 17, wherein the duration of each off / on cycle is between about 0.5 seconds and about 10 seconds, preferably.

19. An apparatus according to claim 17 or 18, wherein the duration of each off / on cycle is about 1 second.

20. An apparatus according to any of claims 17 to 19, wherein within each off / on cycle, the light source is off for between about 10% and about 40% of each cycle.

21. An apparatus according to any of claims 17 to 20, wherein within each off / on cycle, the light source is off for about 25% of each cycle.

22. An apparatus according to any of claims 17 to 21, wherein the light source emits light at wavelengths which mimic sunlight.

23. An apparatus according to any of claims 17 to 22, wherein the light source emits blue, green, red and far red light.

24. An apparatus according to any of claims 17 to 23, wherein the light source emits a spectrum of light from a wavelength of about 280nm to a wavelength of about 800nm.

25. A building or structure for growing strawberry plants, wherein the building or structure comprises one or more apparatus according to any of claims 17 to 24.

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