Winter crops like Primula, Viola, Pansy, Ranunculus and other Biennials and Perennials, face a number of risks this season. Low light levels, cold temperatures and high relative humidity, can lead to damaged leaves and flowers and even to root fungi development.
These risks, however, can be minimized with a few steps, says Ben Geijtenbeek, Senior Crop Technical Specialist at Syngenta Flowers, based at Enkhuizen in the Netherlands.
He maintains healthy winter crops in two ways: first, by starting with the right genetics; and second, by controlling what he calls “the essential growing factors” in the greenhouse.
Ben says, “Keep plants in good condition by giving quite high EC (electric conductivity) levels from the start, maintaining the right element balance, EC and pH (acidity), cleaning the greenhouse to achieve maximum light levels, and keeping a good balance between temperature and light levels.”
A little heat is good, he says. It keeps plants active and lowers humidity levels. However, it should be controlled. Ben advises heating less in dark conditions and allowing temperatures to rise on a sunny day, emulating nature. Watering from below, to keep leaves dry, is also important when maintaining climate control.
Ventilation should continue day and night with plants spaced at a healthy distance to allow air to flow freely around them.
Even in frosty weather, ventilation should be continued but – critically – growers should avoid plants regularly going through ‘the zero degrees zone’. It is better to maintain one temperature; either below zero with extra ventilation or just above zero.
“I prefer the second option,” says Ben, adding, “but when a frosty period is forecast, remember to give plants sufficient water to avoid pots drying out. And if it snows, remove it from the greenhouse roof as snow absorbs and reflects the urgently needed light.”
Good climate management and culture control can greatly minimize the risk of winter damage. This will reduce your reliance on chemicals (which Ben says are less effective in lower temperatures anyway), and mean less labour. And, of course, a healthier crop will lead to better sales.