As soon as the sun comes out and the days get longer, your green fingers start itching. How tempting it is to plant geraniums and other summer flowers on the balcony and terrace at the beginning of May! But this may not be a good idea. Even with hardy geraniums, growth decreases considerably at temperatures below 12°C. If the temperature drops below 5°C, it comes to a complete standstill. Frost can cost them their lives. This is why you should waiting until there are no more night frosts and temperatures reach double-digits during the day before planting. This is usually around mid-May. But if, despite all your patience, a cold snap happens, there are ways to help geraniums survive short periods of colder temperatures unscathed. The experts at PfE share ten helpful tips:
Tip 1: Close to the house wall
Near the wall of your house, geraniums benefit from the waste heat of the building. Walls are good heat accumulators that moderate the temperature difference between day and night.
Tip 2: Not directly on the ground
Ground frost can even occur when a thermometer at eye level still shows plus degrees. Cold air not only drops downwards, but also collects there. If you want to be on the safe side, place your geraniums in a raised position. A layer of newspaper under the pots can also have an insulating effect.
Tip 3: Under the roof
Warm air rises, cold air falls. So it makes sense to place planted boxes and containers under a roof (and preferably also close to a wall) on cool nights. Temperatures are milder here than outdoors.
Tip 4: Cover in the evening
A garden fleece, bubble wrap or a bed sheet can keep the cold away from your plants. You can also cover them with a cardboard box to protect them at night. During the day, remove any dark cover to allow light to reach the plants. A garden fleece can be left in place for longer.
Tip 5: Stay away from balcony railings
It’s not a good idea to leave balcony boxes hanging from the railing when there’s a risk of frost. This spot is probably the one place around your home that is most exposed to wind and weather. Using a fleece can help plants survive frosty nights. Even better: take down boxes and move them to the wall of the house or place them in a sheltered indoor area.
Tip 6: Frost-free emergency shelter
If it gets really cold, geraniums need to be moved temporarily, but their stay indoors should be as short as possible. They can survive several days in a garage or frost-free garden shed.
Tip 7: Low water requirements
As much as geraniums enjoy daily watering in the summer heat, they should be watered very sparingly at the beginning of the season. At low temperatures, their metabolism slows down so they need little water. This also applies if there is another cold spell later in the year. Keyword: late cold snap.
Tip 8: Consider the weakest link
When it comes to getting mixed summer flower combinations through a short cold spell in good condition, the weakest link sets the pace. Most of the summer flowers traded in Europe do not want to be kept cooler than 5°C – just like geraniums.
Tip 9: Install a weather app
How do you know when a ground frost is imminent? Weather apps help you assess the situation. Checking the forecast every evening should be part of your routine, especially at the beginning of the growing season, but it’s better not to rely on the forecast alone. The actual conditions depend on many factors such as buildings in the vicinity, wind and humidity.
Tip 10: When it happens
If your geraniums do suffer a light frost, it’s not a catastrophe. As long as only the leaves freeze, the plants can regenerate. For this to happen, the stem and root tissue must be intact.
Why don't geraniums tolerate frost?
Geraniums cannot tolerate frost because they don’t have to in their native habitat. The geranium comes from South Africa, more precisely from the region around Table Mountain. The climate there is like that of the Steppes. It rains very little and the average annual temperature is 25°C. Even in the winter months, the thermometer almost never falls below 5°C. Temperatures close to zero signal to the geranium that it’s winter now.
It takes a break from growth, from which it must first recover. By way of comparison: in 2021, the German Weather Service identified Cologne-Stammheim as the warmest place in Germany. The average annual temperature there was only 11.4°C!
Detailed advice on all aspects of geranium care is available at specialist retailers.