April can be quite a roller-coaster of weather events. Night-time frosts and heavy hail showers intertwined with beautifully warm sunny days keep the daily greetings interesting. However, these ever-changing conditions can be a challenge to manage in a greenhouse setting at a time when so many seedlings are just getting established. So, this month we will discuss ways to counter some of these extreme swings.
Ventilation to let in fresh air is essential in any greenhouse. Plants require a steady supply of CO2 as they turn it into oxygen, so they can’t exist long-term in a closed off environment. Ventilation can also be used to adjust the temperature and humidity.
Temperature requirements vary between plants, but as a rule of thumb night-time temperatures between 12 and 19C and day-time temperatures between 21 and 26C are considered optimal for growth. Once temperatures go beyond 29C plants can suffer distress. A simple thermometer can be useful in monitoring this.
Ways to increase night-time temperature include closing vents overnight (preferably before sunset) to retain the daytime heat. Covering sensitive plants with frost-protection fleece or bubble-wrap can further help retain heat and protect from overnight frost.
Ways to lower temperature during particularly warm or sunny days include opening all doors and vents, the use of fans or shade netting and watering the path or other solid areas. These processes can be automated by temperature-sensors or timers.
Too much humidity sets conditions for moulds and diseases, which can be lowered by simply allowing a better flow of air via ventilation.
Inadequate humidity is usually only an issue in Ireland during a heat wave but can still lead to plant distress. Adding moisture by watering is the obvious antidote. Since day-time watering can lead to sun-scorch, watering is best done either in the morning or in the evening. But in intense heat, watering the ground or solid surfaces during the day can be useful to both slightly lower the temperature and increase humidity.
Glasshouses receive fresh air through doors, roof vents or side vents which can be easily automated. Ceiling fans can also be fitted.
Fortunately, plants are resilient enough to withstand natural fluctuations in conditions. So, with a little bit of extra care, they can really thrive in the enhanced environment provided by your greenhouse. And so can you!