Project title: Practical demonstration of scheduling techniques for flowering patio plants
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Table 3. The effect of temperature, daylength and supplementary lighting on increasing the height/length of the longest shoot (in cm) at marketing of a range of patio plants. For example, Antirrhinum ‘Deep Purple’ plants were 5cm taller at marketing in the 5°C compartments when compared with the 15°C compartments.
1 Difference reduced if temperature reduced 2 Difference reduced if pinched 1.4. Financial benefits The financial benefits of earlier flowering are difficult to quantify. If product currently sold without flower and can be brought into flower for marketing, then there may be an increase in the value of the product. Whilst for most patio and basket plants the advantage of hastening of flowering will be a reduction in cropping time. However, reductions in cropping times will only be of financial value if the space that is freed up can be utilised for an additional crop, or if the same throughput is achieved from a smaller production area. The cost of lighting has been calculated using a range of electricity tariffs, based on the set up and treatments used in the trial at Wellesbourne (Table 4). These calculations are based on one 400W SON/T lamp every 10 m2 drawing 435W electrical power for 8 hours per day, or one tungsten lamp (100W) every 4.5 m2 for on average 6 hours per day to extend the daylength. Some caution is needed when scaling up these figures for commercial houses as the lighting can probably be applied more efficiently over larger areas. Installation and maintenance costs would also need to be considered. The duration and hence cost of LD lighting could be reduced if night-break lighting were used instead of day-extension lighting. Costs could also be reduced by using compact fluorescent lamps and/or lowering the lamps so that they are nearer to the height of the bench, although it would be important to ensure the light levels were still reasonably even across the crop. The cost of lighting with one compact fluorescent (25W) every 4.5 m2 for 2 hours per day is shown for comparison. Table 4. The cost of lighting with tungsten, SON/T and compact fluorescent lamps based on a range of different electricity tariffs. See text for details.
The costs of raising the temperature will depend on the weather conditions and the environmental strategy that is chosen. Raising the heating set-points would have fuel cost implications. An alternative and more cost effective solution would be to increase vent temperatures to maximise solar gain. However, this may result in increased humidity and so care should be taken to monitor humidity and introduce humidity control strategies. 1.5. Action points for growers
Science section 2.1. Introduction Patio plants have become an increasing part of the bedding and pot plant industry for spring and summer sales. They are often vegetatively propagated and ideally the finished product is sold in flower. These plants are estimated to have a farm gate value of £50M (DEFRA statistics 2001/02). Many plants use daylength as a signal for floral induction. Unlike temperature or light level, the daylength for a particular latitude on any given day of the year is always the same, so this can be used by plants as an indicator of the time of year, even during unseasonal weather conditions. Plants are categorised as either short day plants (SDP), long day plants (LDP) or day neutral plants (DNP). LDP and SDP can then be subdivided into obligate (qualitative), where a particular photoperiod is essential for flowering, or facultative (quantitative), where a particular photoperiod can hasten flowering but is not essential (Thomas and Vince-Prue, 1997). However, daylength alone is an ambiguous signal in spring and autumn and, hence, some plants use a combination of photoperiod and chilling (vernalisation) to ensure that they flower in spring and not in autumn. Furthermore, temperature usually affects flowering time even in species that do not require chilling; as is the case with many biological processes, the rate of progress to flowering is affected by temperature. The effect of temperature on the timing of developmental events such as flowering can usually be attributed to mean diurnal temperature rather than distinct day/night effects. There also is evidence to suggest that for a number of species the time to flowering can be hastened by increased light levels. This work sets out to demonstrate a screening protocol that could be used by growers on their own nurseries to quantify the way in which different species/cultivars respond to their environment, as well as providing valuable information on the responses of 30 different cultivars (14 species). The trial was designed to address the following questions:
2.2. Materials and methods Plants were grown in four identical glasshouse compartments (E1, E2, E3 and E4) each 41m2. Two compartments were set to provide a heating temperature of 5oC, and the other two were set to 15oC. Vent temperatures were set to 3°C above these heating set-points. At each temperature, one compartment initially provided natural short days (SD) and the other received day-extension lighting (LD) provided by tungsten bulbs (~1.7 µmol/m2/s at bench height (~ 100 lux)) so as to give a minimum daylength of 15 hours (lit from sunset to 23:00 h (GMT)). To avoid problems associated with light pollution in the SD compartments, blackout screens were used on the walls of each compartment from sunset until sunrise.    
Figure 1. Photographs showing the linear array of experimental glasshouse compartments and the internal layout of plants and lamps. Within each compartment, half of the plants received supplementary lighting, which was provided by two 400W SON/T lamps per compartment. At plant height supplementary light levels were on average 41µmol/m2/s (~3000 lux). SON/T lamps were baffled so that the unlit treatment in the same compartment was unaffected. The supplementary lighting was on for 8 hours per day from 08:00 - 16:00 h (GMT). Plants (30 cultivars of 14 different species) were obtained as rooted cuttings from commercial propagators. Plants arrived from week 2 to week 5. Cuttings were potted up into 9cm pots containing Levington M2 compost on arrival at Warwick HRI. Plants were watered for the first two to three weeks, they were then initially fed with Vitafeed 111 and subsequently Vitafeed 102 (0.67g/l) was used for the bulk of the experiment. Twenty plants were grown in each treatment; 10 in a block in the north half of the compartment and 10 in the south half. The blocks of plants were placed in the same relative positions in each compartment. The only exceptions were Fuchsias, Petunia and Diascia, where only 10 plants were grown per treatment. Some species were already pinched before they arrived at Warwick HRI, others were pinched after potting up. Some of the Fuchsias and Lotus were pinched a second time to maintain more compact plants. In these cases half of the plants were pinched (as would have been done commercially) and half were left unpinched as so not to remove potential flower buds and affect flowering times. Plants were treated for P&D problems as required. Some of the Fuchsias arrived with Botrytis cinerea which spread within the compartments in particular to other Fuchsias and Antirrhinums. Consequently, plants were sprayed with Bavistin (0.5 g/l) for three consecutive weeks. This was followed by one application of Bravo 500 (4 ml/l), and one application of Scala (2ml/l) which caused some leaf scorch to a few species (in particular Lobelia and Sanvitalia). As fungicides that would leave spray deposits were undesirable, Rovral WP (1g/l) was subsequently used in a regular spray programme for the control of Botrytis. Some aphids were observed on the Fuchsias in one compartment towards the end of the experiment, these were sprayed with Pyrethrin. Biological control agents were used for the control of sciarid fly (plants were drenched with nematodes Steinernema feltiae) and thrips (Amblyseius cucumeris were introduced). Environmental data was recorded via the climate computer (DGT-Volmatic; LCC 1200 Super 4 climate computer) and a number of independent sensors. This included using thermistor sensors (10kΩ Fenwall thermistors) inserted into the aspirated screens and four light sensors (quantum sensors; Skye Instruments Ltd) were also positioned in the compartments just above the crop. These sensors were connected to a data-logger (DL2, Delta-T Devices Ltd) set to scan every 60 seconds and record every 10 minutes. Plants were inspected three times a week so that dates of visible bud appearance and flower opening could be recorded for each plant. Visible bud was defined for each species (Appendix 2) and flowering was taken to be the time when the first flower of each plant opened. The plant height, or in the case of trailing species the length of the longest shoot, was recorded for each plant when 50% of the plants of a given treatment had flowered. All of the flowering and bud appearance times are expressed as the number of days from potting up, which is when the treatments started. 2.3. Results and discussion The DGT and independent sensors showed good agreement with regards to the air temperatures. When small deviations were observed the sensors were checked and recalibrated. Furthermore, the compartments that had the same set-points had similar temperature regimes (Figure 2). The 15°C compartments initially ran slightly above this set-point and temperatures were fairly stable, while the 5°C compartment fluctuated more with changes in ambient temperature. The difference between the 5 and 15°C compartments diminished over the course of the experiment as the ambient temperatures increased over time. 
Figure 2. Air temperatures (24hr averages) recorded for the four glasshouse compartment over the course of the experiment. Light levels increased over the course of the experiment (Figure 3). The supplementary lighting gave a fixed quantity of light which had a proportionally larger effect early in the year when the quantity of natural light was low. The natural daylength also increased over time (Figure 4). Lighting from sunset to 23:00 h (GMT) with tungsten lamps gave a minimum daylength of 15 h, although this also increased over the course of the experiment due to an earlier sunrise. The plants results are presented by species and cultivar listed in alphabetical order. 
Figure 3. Light levels (PPFD) recorded in the glasshouse compartments over the course of the experiment. The increase due to supplementary lighting is shown. 
Figure 4. The change in natural daylength (SD) over the course of the experiment. The effect of lighting from sunset to 23:00 h (GMT) can also be seen (LD). 
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