Plant propagation tray and method for breeding plants

Abstract

A plant propagation tray for growing plants, in particular chrysanthemums, the tray comprising a plurality of tray holes for holding substrate material, wherein each tray hole comprises a top opening for receiving the substrate material in the tray hole and a bottom opening, wherein the top opening is shaped as a squircle, rounded square or truncated circle, wherein each tray hole is defined by a frustoconical sidewall extending downwards from the top opening to the bottom opening in an increasingly tapering manner.

Description

[0001] PLANT PROPAGATION TRAY AND METHOD FOR BREEDING PLANTS

[0002] The present application relates to a plant propagation tray and a method for growing plants, in particular Asteraceae, more in particular chrysanthemums, from plant cuttings.

[0003] Plant propagation trays typically comprise a plurality of tray holes for holding substrate material, wherein each tray hole comprises a top opening for receiving the substrate material in the tray hole and a bottom opening for water drainage, wherein each tray hole is defined by a frustoconical sidewall extending downwards from the top opening to the bottom opening. Such trays are commonly used in greenhouses to grow plants from seeds planted in substrate held in the tray. After the plants are grown, they can be automatically extracted from the tray by a machine, which inserts a number of elongated members through the top opening into the tray hole to engage the growth substrate and plant roots. Often, the plants are then planted in for example soil to continue growing, after which the plants are finally harvested.

[0004] However, some plants, like Asteraceae, in particular chrysanthemums, although they are commonly grown in greenhouses, are typically grown from cuttings instead of seeds. A cutting is taken from, for example, an existing chrysanthemum, and planted in a substrate to grow for a certain amount of time, after which it is planted in for example soil to continue growing, after which it is harvested.

[0005] Typically, to grow a plant from a cutting instead of a seed, a substrate of a larger volume is needed to ensure proper plant growth in an efficient manner. However, although a larger substrate volume enhances the growth of the plant, in particular of its roots, a limitation is that plants in substrate in holders of such volume are difficult to remove from their holder using a machine. Plants grown from cuttings are therefore grown in compressed clods. However, this growing method has limited efficiency and limits overall productivity, and is less suitable for use in automated processes such as automated planting and / or removal of more developed plants from the substrate.

[0006] It is an object of the present invention, amongst other objects, to provide an improved plant propagation tray for efficiently growing plants from plant cuttings, more specifically wherein the weight and / or surface area of the leaves that develop from the cutting during the growth period, in particular while the cutting is held in the propagation tray, can be maximised.

[0007] This object is at least partially achieved by a plant propagation tray and a method according to the appended claims. In particular, this object is at least partially achieved with a plant propagation tray for growing plants, in particular chrysanthemums, the tray comprising a plurality of tray holes for holding substrate material, wherein each tray hole comprises a top opening for receiving the substrate material in the tray hole and a bottom opening, wherein the top opening is shaped as asquircle, rounded square or truncated circle, wherein each tray hole is defined by a frustoconical sidewall extending downwards from the top opening to the bottom opening in an increasingly tapering manner.

[0008] This tray allows for automatic extraction of the plant and substrate using a machine, due to the roundness of at least the corners of the top opening of the tray hole, while the overall squareness of the shape of the top opening optimises the volume of the tray hole for holding substrate. That is, a square-like shape of the top opening increases the ratio between the volume of a tray hole and the total number of tray holes which can be fit in a unit of area of a tray, such as holes per square meter of tray. At the same time, the rounded corners of the tray hole prevent clumps of the substrate from breaking off the substrate when the substrate is extracted. In addition, the rounded corners prevent roots from concentrating in the corners of the substrate, instead spreading more homogeneously through the substrate volume. The increasingly tapering shape of the sidewall allows for a maximized inner volume, while still preventing clumps of the substrate from remaining in the tray hole when extracting the plant and substrate using a machine. To prevent roots from growing out of the bottom opening of the tray hole, the bottom opening of the tray hole is preferably exposed to air, and / or air can be blown underneath the tray. This is called air pruning and causes the cutting to keep developing new and heathy roots inside the substrate in the tray hole such that the plant growth can be enhanced.

[0009] Preferably, the sidewall has a total height defined by the distance between the bottom opening and the top opening, wherein an upper segment of the sidewall extends downwards from the top opening and has a length of 50-70%, preferably of 50-60%, of the total height of the sidewall, wherein the sidewall of the upper segment tapers in a straight manner. This straight taper in the upper part of the tray hole enables the tray hole to have a sufficiently large volume.

[0010] Additionally, it is preferred if a middle segment of the sidewall that extends downwards from the upper segment has a length of 30-50%, preferably of 35-45%, of the total height of the sidewall and curves inwards, wherein a lower segment of the sidewall that extends downwards from the middle segment towards the bottom opening has a length of 0-20%, preferably of 2-6%, of the total height of the side wall and curves inwards towards the bottom opening. The inward curvature facilitates the automatic extraction of the substrate by a machine.

[0011] Thus, especially in combination, the above features of said sidewall segments provide an optimal shape of the tray hole for maximum volume and which allows automated extraction of the substrate and prevents clumps of substrate breaking off and remaining in the tray hole.

[0012] Preferably, the tray is arranged to fit onto an identical tray, allowing multiple trays to be stacked. Due to the shape of the tray holes, the stackability of the tray can be greatly enhanced. Inparticular, the compactness of a stack of the trays can be enhanced such that the volume of the stack is about 40% less than a stack of the same number of trays of the known type.

[0013] Preferably, the width of the top opening is in the range of 30-50 millimetres, preferably 35-38 millimetres, wherein the smallest width of a lower end of the middle segment where it couples to the lower segment is in the range of 15-20 millimetres. This allows for an optimal inner volume of the tray hole, while also optimizing the number of tray holes per square meter.

[0014] Preferably, the bottom opening is substantially circular. This allows for a robust construction of the tray hole.

[0015] Preferably, each of the tray holes has an inner volume of at least 25 cubic centimetres, preferably at least 30 cubic centimetres, more preferably at least 40 cubic centimetres, for example in the range of 40-75, preferably between 40-50 cubic centimetres. This provides for an optimal combination of tray hole volume, and number of tray holes per square meter.

[0016] Preferably, the sidewall has a total height defined by the distance between the bottom opening and the top opening, wherein the total height of the tray hole is in the range of 50-55 millimetres. This optimizes the volume of the tray hole, while limiting the total height of the tray hole. A larger height makes for more difficult extraction of the substrate, and requires more overall space.

[0017] Preferably, a diagonal of the top opening is at most 42 millimetres. This provides for an optimal combination of tray hole volume, and number of tray holes per square meter.

[0018] Preferably, the diameter of the bottom opening is in the range of 8-16, preferably 10-14 millimetres. This allows for optimal root development and air pruning.

[0019] Preferably, the cross-sectional shape of the first and second sections are substantially square with rounded corners. This maximizes the volume of the tray hole.

[0020] Preferably, the cross sectional shape of the third section is, for at least part of the length of the third section, substantially square with rounded comers. This maximizes interior volume while allowing for, for example, a round bottom opening.

[0021] Preferably, the tray has a tray hole density in the range of 530-620 tray holes per square metre of the tray.

[0022] Another aspect of the present disclosure relates to a mould for manufacturing a tray according to any of the preceding claims, in particular by injection moulding.

[0023] Another aspect relates to a method for growing plants, in particular chrysanthemums, from plant cuttings, comprising the steps of:providing a plant propagation tray comprising a plurality of tray holes;

[0024] filling the plurality of tray holes with a growth substrate;

[0025] planting a plurality of plant cuttings in the growth substrate in the plurality of tray holes, respectively;

[0026] growing the plurality of cuttings for a first period of time;

[0027] Preferably, the step of providing a plant propagation tray comprises the step of providing a plant propagation tray with tray holes having an inner volume of 40-75 ml. This allows for a longer duration of the first period, increasing the size of the cuttings and increasing the yield and quality of harvested chrysanthemums. A larger volume allows for a longer first period of time, but also requires more space.

[0028] Preferably, the step of providing a plant propagation tray comprises a step of providing a plant propagation tray as described above. This tray provides the optimal features to conduct the above mentioned method, while minimizing the amount of space required.

[0029] Preferably, the method further comprises a step of progressively increasing the EC value of the substrate from 1 to 1.5-2.0, preferably 1.8, mS / cm during the first period of time. This increases the growth of the cuttings.

[0030] Preferably, the method further comprises the step of providing plant nutrition to the cuttings after 8-12, preferably 10, days. This increases the growth of the cuttings, and allows for a longer time spent in the propagation trays.

[0031] Preferably, the plant nutrition comprises a mixture of water, containing at least one or more of nitrogen, phosphate, potassium, calcium, magnesium, sulphur, micronutrients. This provides optimal nutrition to the chrysanthemums.

[0032] Preferably, the step of providing plant nutrition comprises providing a mixture comprising at least water, mixed with one or more of calcium nitrate, potassium nitrate, magnesium sulphate, mono ammonia phosphate, chelated iron DTPA, micronutrients.

[0033] Preferably, the first period of time is at least 14, preferably at least 16 days. A shorter period of time is used in the state of the art, as otherwise the size discrepancy of the cuttings becomes unacceptable. However, the longer duration, in combination with the aforementioned steps, allows of an improved yield while reducing the size discrepancy.

[0034] Preferably, the method further comprises a step of, during a first light phase, exposing the cuttings to a first RGB light spectrum comprising 25 - 35%, preferably 29 - 33%, most preferably 31% ofred light, 60 - 70%, preferably 62 - 66%, most preferably 64% of blue light, and 0 - 10%, preferably 3 - 7%, most preferably 5% of green light.

[0035] Preferably, the first light phase comprises 6 - 8 days, preferably 7 days, wherein the cuttings are preferably exposed to 12 hour cycles of the first light spectrum, wherein each 12 hour cycle comprises 8 - 11 hours of exposure to the first light spectrum, and 1 - 4 hours of no exposure to the first light spectrum. Preferably, a period of light exposure to the first light spectrum is followed by a period of 10 - 30 minutes, preferably 20 minutes, of exposure to far-red light, wherein far-red light is light with a wavelength of approximately 700-750, preferably 730 nanometres. Preferably, the cuttings are exposed to far-red light at an intensity of 4 - 6, preferably 5 micromole per square meter per second (pmol / m2 / s). Preferably, the cuttings are exposed to the first light spectrum on day 1 of the first light phase with an intensity of 15 - 25, preferably 20 pmol / n / s, wherein the light intensity is preferably increased with 5 - 15, preferably 10 pmol / m2 / s each subsequent day, or at least such that the light intensity reaches 70 pmol / m2 / s after 5 - 7, preferably 7, days. This stimulates root development of the cuttings, as well as auxin activity through hormonal signals resulting from stimulation by especially the far-red light exposure, while minimizing energy usage. Preferably, the method further comprises a step of exposing the cuttings to a second light phase, preferably starting on day 5 - 9, preferably 6 - 8, more preferably day 7 after the start of the first period of time, preferably after the first light phase, wherein in the second light phase the cuttings are exposed to a second light spectrum comprising 70 - 80% of red light, 15 - 25 % of blue light, 0 - 5% of green light, and 0 - 5% of far-red light,. Preferably, the second light phase comprises 6 -10, preferably 8 days, following the first light phase. Preferably, the cuttings are exposed to the second light spectrum at an intensity of 120 - 240 pmol / m2 / s. Preferably, the second light phase comprises 24 hour cycles, wherein cuttings are exposed to the second light spectrum for 18-22 hours, and not exposed to the second light spectrum for 2-6 hours. Preferably, the period of no exposure to the second light spectrum coincides with night time. This accelerates root development and optimizes photosynthesis, as well as supporting leaf spread and light penetration.

[0036] Preferably, the method further comprises a step of exposing the cuttings to a third light phase, starting on day 10 - 14, preferably 11 - 13, more preferably day 12 after the start of the first period of time, preferably after the second light phase, wherein the cuttings are exposed to a third light spectrum comprising 40 - 60% of red light, 40 - 60% of blue light, and 0 - 5% of green light, and preferably 0% of far-red light. Preferably, the third light phase comprises 7 - 11, preferably 9 days or less. Preferably, the cuttings are exposed to the third light spectrum at an intensity of 250 - 400 pmol / m2 / s. Preferably, the third light phase comprises 24 hour cycles, wherein cuttings are exposed to the third light spectrum for 18-22 hours, and not exposed to the third light spectrum for 2-6 hours. Preferably, the period of no exposure to the third light spectrum coincides with night time.Preferably, the cuttings are not exposed to far-red light during the third light phase. This facilitates compact plant growth, improving the resilience and robustness of the plants.

[0037] It will be appreciated that the aforementioned characteristics of respectively the first, second and third light phases and light cycles are independent of each other.

[0038] Preferably, the method additionally comprises the steps of:

[0039] removing the plurality of cuttings, grown for said first period of time, from the tray; sorting each of the grown cuttings into a plurality of categories, based on at least one characteristic of a cutting;

[0040] planting the sorted cuttings based on the respective category.

[0041] This allows for an increase in the time the cuttings spend in the propagation trays, i.e. the first period of time. As this time increases, the discrepancy in the sizes (height, and / or leaf weight) of the cuttings increases. The sorting step subsequently allows the discrepancy to be reduced by sorting the cuttings into categories.

[0042] Preferably, the first period of time corresponds to the time taken for at least one of the cuttings to reach a predetermined target height, preferably a height of 8-30cm, preferably 8-20cm, more preferably approximately 20cm.

[0043] Preferably, the at least one characteristic of a cutting comprises a total height of the cutting, and wherein the plurality of categories represents a plurality of different height ranges. Additionally or alternatively, at least one characteristic is indicative of an aesthetic characteristic such as colour. Preferably, the step of planting the sorted cuttings based on the respective category comprises planting the cuttings together with the first growth substrate into a second growth substrate.

[0044] Preferably, the method further comprises exposing the bottom of the tray to air, preferably moving air, thereby exposing the bottom openings of the tray to air, preferably moving air.

[0045] Preferably, the method further comprises a step of blowing air across the bottom of the tray, in particular across the bottom openings of the holes of the tray. This induces the roots to continue growing.

[0046] Preferably, the step of sorting the plurality of cuttings comprises a step of automatically sorting the plurality of cuttings using a sorting machine. This allows for an efficient sorting of the cuttings. The present invention is further illustrated by the following Figures, which show a preferred embodiment of the device according to the invention, and are not intended to limit the scope of the invention in any way, wherein:figures 1 and 2 show perspective views of a propagation tray;

[0047] figure 3 shows a more detailed overview of a tray hole;

[0048] figures 4 and 5 show frontal and side views of the propagation tray;

[0049] figures 6-8 show cross sectional views of the tray holes;

[0050] figure 9 shows an example of an improved growth compared to a control group; and figure 10 shows the EC value of an improved growth compared to a control group.

[0051] Figure 1 shows a perspective view of a plant propagation tray 1 , comprising a plurality of upwards opening holes 2 for holding a substrate material for plants to grow in. Figure 2 shows a perspective view of the tray 1 seen from the bottom. The plurality of holes 2 each comprise a sidewall 4 which tapers from the top opening (not shown) to a bottom opening 5.

[0052] Figure 3 shows a more detailed overview of a tray hole 2. The hole 2 has a top opening 3, comprising straight sidewall sections S, thus following tangent lines La, Lb, and rounded comers with a radius r. The shape of the opening 3 thus follows a square shape with rounded edges. The width W and length D are 36mm. The sidewall 4 is divided in three sections, 4a-c, shown in more detail in figure 6. At the bottom of the tray hole 2 the sidewall 4 ends in a bottom hole 5 of diameter d, being 10-14mm.

[0053] Figures 4 and 5 show side and front views of a tray 1. The tray comprises 14 x 10 = 140 holes, but variants with more or fewer holes are conceived.

[0054] Figures 6-8 show cross sectional views of a tray 1 , in particular of one or more tray holes 2.

[0055] Notches 6 are arranged near the top openings 3, and extend between adjacent holes 2. In the shown embodiment these notches 6 only extend between adjacent holes 2 in one direction. However, embodiments with notches 6 that connect one hole to adjacent holes 2 also in the second, perpendicular, direction are also envisioned. These notches 6 allow for a degree of communication between adjacent holes, such that for example nutrients may move between adjacent holes 2 to improve and homogenize the cultivation environment. As shown in particular in figure 8, the sidewall 4 can be divided into three sections 4a-c which progressively taper. The first sidewall section 4a follows a substantially conical profile. In other words, the sidewall 4a is straight, but tapers inwards at an angle a of 1-15°, preferably 1-10°, more preferably 5°. The second sidewall section 4b connects to the first sidewall section in plane Ia. The second sidewall section 4b is curved, and progressively curves inwards from approximately angle a to angle B, B being 15-50°, preferably 35-45°, more preferably 40°. The third sidewall section 4c connects to the second sidewall section 4b in plane lb, and tapers from approximately angle B to angle y, of approximately 45-70°, preferably 50-65°, more preferably 58°. The height ha of the first sidewall section 4a isapproximately 30mm, the height hb of the second section 4b is approximately 22mm, and the height hcof the third section 4c approximately 2.5mm. The resulting total height h of a tray hole 2 is approximately 54.5mm. The cross section of the sidewall 4 remains substantially square with rounded edges up to plane lb, after which it transitions to circular to end in the bottom hole 5, which is circular.

[0056] Figure 9 shows a graph illustrating the effect of an improved nutrition cycle on chrysanthemum growth. The graph indicated as “Control Growth (g)” is representative of the growth of a control group, and the graph indicated as “Improved Growth (g)” is representative of a test group of cuttings. A plurality of cuttings was grown, each in a substrate of approximately 45ml. The pH value of the substrate was approximately 5.5, and the electric conductivity (EC) value approximately 1 mS / cm. The substrate comprises approximately 75% peat, and 25% moss peat. The substrates were allowed to grow for 20 days. During this time, the control group was not provided with additional fertilization or other plant nutrition. The test group was provided, from day 10 with a nutrition mixture comprising water with dissolved therein:

[0057]

[0058] The nutrition mixture was produced using the following compounds:

[0059]

[0060]

[0061] Figure 9 shows a notable increase in growth, expressed in grains, in the test cuttings.

[0062] Figure 10 shows a graph of the EC value during the test. The substrates of the control group were maintained at an EC value of 1 mS / cm, while the EC value of the test cuttings was increased approximately linearly from day 10 to day 17 from 1 to 1.8 mS / cm.

[0063] The drawings and the above description serve to illustrate specific embodiments of the invention and do not limit the scope of protection defined by the appended claims.

[0064] The following embodiments are further provided for illustrative purposes.

[0065] 1. A plant propagation tray for growing plants, in particular chrysanthemums, the tray comprising a plurality of tray holes for holding substrate material, wherein each tray hole comprises a top opening for receiving the substrate material in the tray hole and a bottom opening, wherein the top opening is shaped as a squircle, rounded square or truncated circle, wherein each tray hole is defined by a frustoconical sidewall extending downwards from the top opening to the bottom opening in an increasingly tapering manner.

[0066] 2. Tray according to embodiment 1, wherein the sidewall has a total height defined by the distance between the bottom opening and the top opening, wherein an upper segment of the sidewall extends downwards from the top opening and has a length of 50-70%, preferably of 50-60%, of the total height of the sidewall, wherein the sidewall of the upper segment tapers in a straight manner, wherein a middle segment of the sidewall that extends downwards from the upper segment has a length of 30-50%, preferably of 35-45%, of the total height of the sidewall and curves inwards, wherein a lower segment of the sidewall that extends downwards from the middle segment towards the bottom opening has a length of 0-20%, preferably of 2-6%, of the total height of the sidewall and curves inwards towards the bottom opening.

[0067] 3. Tray according to embodiment 2, wherein the width of the top opening is in the range of 35-38 millimetres, wherein the smallest width of a lower end of the middle segment where it couples to the lower segment is in the range of 15-20 millimetres.4. Tray according to any of the preceding embodiments, wherein the bottom opening is substantially circular.

[0068] 5. Tray according to any of the preceding embodiments, wherein each of the tray holes has an inner volume of at least 25 cubic centimetres, preferably at least 30 cubic centimetres, more preferably at least 40 cubic centimetres, for example in the range of 40-50 cubic centimetres 6. Tray according to any of the preceding embodiments, wherein the sidewall has a total height defined by the distance between the bottom opening and the top opening, wherein the total height of the tray hole is in the range of 50-55 millimetres.

[0069] 7. Tray according to any of the preceding embodiments, wherein a diagonal of the top opening is at most 42 millimetres.

[0070] 8. Tray according to any of the preceding embodiments, wherein the diameter of the bottom opening is in the range of 10-14 millimetres.

[0071] 9. Tray according to any of the preceding embodiments, wherein the cross-sectional shape of the first and second sections are substantially square with rounded corners.

[0072] 10. Tray according to embodiment 1 or 2, wherein the cross sectional shape of the third section is, for at least part of the length of the third section, substantially square with rounded corners. 11. Tray according to any of the preceding embodiments, wherein the tray has a tray hole density in the range of 530620 tray holes per square metre of the tray.

[0073] 12. Mould for manufacturing a tray according to any of the preceding embodiments, in particular by injection moulding.

[0074] 13. Method for growing plants, in particular chrysanthemums, from plant cuttings, comprising the steps of:

[0075] providing a plant propagation tray comprising a plurality of tray holes;

[0076] filling the plurality of tray holes with a growth substrate;

[0077] planting a plurality of plant cuttings in the growth substrate in the plurality of tray holes, respectively;

[0078] growing the plurality of cuttings for a first period of time;

[0079] 14. Method according to the preceding embodiment, wherein the step of providing a plant propagation tray comprises the step of providing a plant propagation tray with tray holes having an inner volume of 40-75 ml.15. Method according to the preceding embodiment, wherein the step of providing a plant propagation tray comprises a step of providing a plant propagation tray according to any of the preceding embodiments 1-11.

[0080] 16. Method according to any of the preceding method embodiments, further comprising a step of progressively increasing the EC value of the substrate from 1 to 1.5-2.0, preferably 1.8, mS / cm during the first period of time.

[0081] 17. Method according to any of the preceding method embodiments, further comprising a step of providing plant nutrition to the cuttings after 8-12, preferably 10, days.

[0082] 18. Method according to the preceding embodiment, wherein the plant nutrition comprises a mixture of water, containing at least one or more of nitrogen, phosphate, potassium, calcium, magnesium, sulphur, micronutrients.

[0083] 19. Method according to at least embodiment 17, wherein the step of providing plant nutrition comprises providing a mixture comprising at least water, mixed with one or more of calcium nitrate, potassium nitrate, magnesium sulphate, mono ammonia phosphate, chelated iron DTPA, micronutrients.

[0084] 20. Method according to any of the preceding method embodiments, wherein the first period of time is at least 14, preferably at least 16 days.

[0085] 21. Method according to any of the preceding method embodiments, further comprising a step of, during at least part of a first light phase during the first period of time, exposing the cuttings to a first light spectrum comprising a mixture of red, blue and green light, wherein during at least part of the first light phase, the cuttings are exposed to far-red light.

[0086] 22. Method according to embodiment 21, wherein the first light phase comprises a plurality of cycles of a predetermined length, wherein during one part of the cycle the cuttings are exposed to the first light phase and no far-red light, and for another part of the cycle the cuttings are exposed to far-red light.

[0087] 23. Method according to embodiment 22, wherein, during a cycle in the first light phase, the cuttings are exposed to the first light spectrum for 8 - 11 hours, and then exposed to 10 - 30, preferably 20, minutes of far-red light.

[0088] 24. Method according to any of the preceding embodiments 22-23, wherein a cycle is 12 hours.

[0089] 25. Method according to any of the preceding embodiments 21 -24, wherein the first light phase comprises the first 6 - 8, preferably 7, days of the first period of time.26. Method according to any of the preceding embodiments 21-25, wherein the first light spectrum comprises 29 - 33% of red light, 62 - 66% of blue light, and 3 - 7% of green light. 27. Method according to at least embodiment 21, further comprising a step of, during a second light phase during the first period of time, exposing the cuttings to a second light spectrum comprising 70 - 80% of red light, 15 - 25% of blue light, 0 - 5% of green light, and 0 - 5% of far-red light, wherein the second light phase starts on day 6 - 8, preferably day 7, after the start of the first period of time.

[0090] 28. Method according to embodiment 27, wherein the second light phase comprises a plurality of 24 hour cycles, wherein during each phase the cuttings are exposed to the second light spectrum for 18 - 22 hours, and not exposed to the second light spectrum during the remaining hours in said 24 hour phase.

[0091] 29. Method according to at least embodiment 21 , further comprising a step of, during a third light phase during the first period of time, exposing the cuttings to a third light spectrum comprising 40 - 60% of red light, 40 - 60% of blue light, and 0-5% of green light, wherein the third light phase starts on day 11 - 13, preferably day 12, after the start of the first period of time.

[0092] 30. Method according to embodiment 29, wherein the third light phase comprises a plurality of 24 hour cycles, wherein during each phase the cuttings are exposed to the third light spectrum for 18 - 22 hours, and not exposed to the third light spectrum during the remaining hours in said 24 hour phase.

[0093] 31. Method according to any of the preceding method embodiments, additionally comprising the steps of:

[0094] removing the plurality of cuttings, grown for said first period of time, from the tray; sorting each of the grown cuttings into a plurality of categories, based on at least one characteristic of a cutting;

[0095] planting the sorted cuttings based on the respective category.

[0096] 32. Method according to any of the preceding method embodiments, wherein the first period of time corresponds to the time taken for at least one of the cuttings to reach a height of 20cm. 33. Method according to any of the preceding method embodiments, wherein the at least one characteristic of a cutting comprises a total height of the cutting, and wherein the plurality of categories represents a plurality of different height ranges.34. Method according to any of the preceding method embodiments, wherein the step of planting the sorted cuttings based on the respective category comprises planting the cuttings together with the first growth substrate into a second growth substrate.

[0097] 35. Method according to any of the preceding method embodiments, further comprising a step of blowing air across the bottom of the tray, in particular across the bottom openings of the holes of the tray.

[0098] 36. Method according to any of the preceding method embodiments, wherein the step of sorting the plurality of cuttings comprises a step of automatically sorting the plurality of cuttings using a sorting machine.

Claims

Claims1. A plant propagation tray for growing plants, in particular chrysanthemums, the tray comprising a plurality of tray holes for holding substrate material, wherein each tray hole comprises a top opening for receiving the substrate material in the tray hole and a bottom opening, wherein the top opening is shaped as a squircle, rounded square or truncated circle, wherein each tray hole is defined by a frustoconical sidewall extending downwards from the top opening to the bottom opening in an increasingly tapering manner, wherein each of the tray holes has an inner volume of at least 40 cubic centimetres.

2. Tray according to claim 1 , wherein the sidewall has a total height defined by the distance between the bottom opening and the top opening, wherein an upper segment of the sidewall extends downwards from the top opening and has a length of 50-70%, preferably of 50-60%, of the total height of the sidewall, wherein the sidewall of the upper segment tapers in a straight manner, wherein a middle segment of the sidewall that extends downwards from the upper segment has a length of 30-50%, preferably of 35-45%, of the total height of the sidewall and curves inwards, wherein a lower segment of the sidewall that extends downwards from the middle segment towards the bottom opening has a length of 2-20% of the total height of the sidewall and curves inwards towards the bottom opening.

3. Tray according to claim 2, wherein the width of the top opening is in the range of 35-38 millimetres, wherein the smallest width of a lower end of the middle segment where it couples to the lower segment is in the range of 15-20 millimetres.

4. Tray according to any of the preceding claims, wherein the bottom opening is substantially circular.

5. Tray according to any of the preceding claims, wherein the sidewall has a total height defined by the distance between the bottom opening and the top opening, wherein the total height of the tray hole is in the range of 50-55 millimetres.

6. Tray according to any of the preceding claims, wherein a diagonal of the top opening is at most 42 millimetres.

7. Tray according to any of the preceding claims, wherein the diameter of the bottom opening is in the range of 10-14 millimetres.

8. Tray according to any of the preceding claims, wherein the cross-sectional shape of the first and second sections are substantially square with rounded comers.

9. Tray according to claim 1 or 2, wherein the cross sectional shape of the third section is, for at least part of the length of the third section, substantially square with rounded corners.

10. Tray according to any of the preceding claims, wherein the tray has a tray hole density in the range of 530 - 620 tray holes per square metre of the tray.

11. Mould for manufacturing a tray according to any of the preceding claims, in particular by injection moulding.

12. Method for growing plants, in particular chrysanthemums, from plant cuttings, comprising the steps of:providing a plant propagation tray according to any of the preceding claims 1-10; filling the plurality of tray holes with a growth substrate;planting a plurality of plant cuttings in the growth substrate in the plurality of tray holes, respectively;growing the plurality of cuttings for a first period of timeremoving the plurality of cuttings, grown for said first period of time, from the tray using a machine for automatic extraction;sorting each of the grown cuttings into a plurality of categories, based on at least one characteristic of a cutting;planting the sorted cuttings based on the respective category.

13. Method according to the preceding claim, wherein the step of providing a plant propagation tray comprises the step of providing a plant propagation tray with tray holes having an inner volume of 40-75 ml.

14. Method according to any of the preceding method claims, further comprising a step of providing plant nutrition to the cuttings after 8-12, preferably 10, days.

15. Method according to any of the preceding method claims, wherein the first period of time is at least 14, preferably at least 16 days.

16. Method according to any of the preceding method claims, wherein the first period of time corresponds to the time taken for at least one of the cuttings to reach a height of 20cm.

17. Method according to any of the preceding method claims, wherein the at least one characteristic of a cutting comprises a total height of the cutting, and wherein the plurality of categories represents a plurality of different height ranges.

18. Method according to any of the preceding method claims, wherein the step of planting the sorted cuttings based on the respective category comprises planting the cuttings together with the first growth substrate into a second growth substrate.

19. Method according to any of the preceding method claims, further comprising a step of blowing air across the bottom of the tray, in particular across the bottom openings of the holes of the tray.

20. Method according to any of the preceding method claims, wherein the step of sorting the plurality of cuttings comprises a step of automatically sorting the plurality of cuttings using a sorting machine.

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