In this section I have tried to give general guidance on how cut flower sweet peas can be grown profitably. It is not intended as a sort of blueprint to be followed meticulously, but rather a set of guidelines which can be adapted to meet individual circumstances. Every locality has its own microclimate, and sweet peas can respond very differently to quite small variations. Much of the information given is based on personal experience, some from feedback from customers in other parts of the world. Ultimately the techniques described will need fine tuning based on your personal experience of your particular growing conditions and the market you are servicing.
Seed will germinate more uniformly if soaked for 24 hours in a suitable fungicide. Any seed that does not swell in this time should have its seed coat nicked and be soaked for a further 12 hours.
In the UK, seed should be sown in early - mid September under gentle heat, 18° to 20°c being ideal. Best results will be obtained by sowing in modules such as the Quickpot 150 deep. The modules should be bottom watered with Filex (Propamocarb hydrochloride) which will protect the young plants from a variety of diseases, including downy mildew. Once the seed has germinated, the young plants should be grown on with only sufficient artificial heat for frost protection, but with maximum light. The growing tip should be pinched out about 3 weeks after sowing when the plants have developed three true leaves.
By mid October the young plants should have developed strong breaks and be ready to be planted out in the glasshouse. A standard 10′ 6″ (3.2m) Venlo bay will accommodate four rows arranged in pairs some 18″ (50cm) apart with 3′ 6″ (1.1m) wide paths. Under UK conditions an in-row spacing of 8″ (20cm) gives stronger plants and better flower quality than a 6″ (15cm) spacing, while having little effect on total yield. This is presumably a consequence of the stronger growth achieved with less competition from neighbouring plants and might not apply in a more favourable climate with higher winter light levels.
Once the plant is well established, one strong basal shoot should be selected. The remains of the seed growth and the superfluous basal shoots are cut away to leave only the selected growth.
As the plant grows, all tendrils and side shoots should be removed on a regular basis. Flower spikes are harvested when approximately half the flowers are open; the exact stage will depend on the exact requirements of individual markets and on storage and transport conditions. Florists supplying weddings or other functions need immediate impact and require a more open product than the traditional bunch trade.
Post harvest treatments are essential to extend vase life if a reputation for quality is to be maintained. Pulsing with Silver thiosulphate for two to four hours followed by cold storage for 24 hours at around 2° centigrade should give a vase life of 7 to 10 days depending on the ambient conditions. Flowers from young vigorous plants have a better vase life than those cut near the end of a cropping cycle.
It is essential that the flowers are protected from sources of ethylene at all times. Ripe fruit is the greatest danger, but ethylene is also a product of incomplete combustion and is released by plants as a response to wounding. This means that the very act of cutting a flower stimulates the release of ethylene by the plant so that the pulsing with Silver thiosulphate, which is an ethylene inhibitor, is always a matter of urgency.
Sweet peas are traditionally sold in bunches of ten stems of a single colour, packed flat, ten bunches to a 30″ flower box. Some markets prefer all the bunches in a box to be of the same shade, others require a good mix of colours. There is considerable scope for themed boxes containing several shades of the same colour.
Presentation is very important if the highest prices are to be realised. The bunches should be secured in the box using "stay-tights" or similar; for long stemmed bunches a single restraint suffices, but three will give a better looking box at the end of the season when stems are short.
© 2006 P. E. M. Rowland