The spring weather is testing us. The sunny days with glorious blue skies are uplifting our spirits, but they are followed by cold, frosty nights. We seem to be experiencing more night frost in Berlin than we have had all winter. Even in my very sheltered small courtyard garden in the center of Berlin, we had -2°C several nights this week. This weather creates an emotional rollercoaster for gardeners: the daytime euphoria of spring sunshine is followed by the anxiety for the well-being of cherished plants. Shrubs with tender shoots like hydrangeas, or the long anticipated precocious blooms of magnolias and the early delicate cherry blossoms can be devastated in one night.
How can you protect your plants from night frosts?
Covering in Water: On frosty evenings fruit growers spray their blossoms with a very fine mist of water. The tiny droplets provide a protective cover over the tender petals. They have also been known to put candles under trees. The old tradition of whitening tree trunks with a protective layer of lime wash provides protection against pests and diseases, but will also help to slow down the tree as the early sunshine will not warm up the trunk. If our Magnolia flowers or ornamental cherry blossoms are damaged by frost it is upsetting as it puts an end to this year’s flower display. For commercial growers this means it puts an end to this year’s harvest.
Fabric Cover: When the plant is not too large, simply throw light fleece over it. There is a special finely spun fabric on the market that you can spread over plants at night. This is extremely light weight so that it will not break tender shoots. Alternatively, use an old bed sheet. I have also made little tents out of a few sheets of newspaper held in place with clothes pegs to protect smaller plants. On these frosty nights it is mostly wind-still so there is no need to seriously anchor the fabric to prevent it from flying off.
Bringing plants indoors: A few years ago all of our freshly delivered clematis were completely damaged by a severe night frost. Since then we no longer take any risks at the Garden Academy: we move most susceptible plants inside on frosty nights. The clematis and tree peonies were given space in one of the greenhouses, whereas the numerous cherries and magnolias as well as the hydrangeas were moved into every other available space: the till and design pavilions were jam-packed as was the disabled toilet . The rest was put into the central corridor and even the office was filled up. It is a lot of work for our diligent gardening team, but worth it. Frosted tips will not kill a plant, but will cause stunted growth and can affect flowering performance.
Hardening off plants
The most susceptible plants are those that have spent their winter in a protected environment such as a glasshouse, cold frame or even just an open polytunnel. Also seedlings raised on your windowsill need a gentle transition period into the garden. Harden them off slowly by bringing then outside during mild spells, initially on overcast days. Alternatively place them in a shady corner of the garden. The direct sunlight can cause the tender leaves to burn on those first few days out. Make sure you cover the plants when the nights are cold. After a week to ten days they should have adapted themselves to their new environment.
Not everything is endangered!
Most plants that have spent the winter in your garden are perfectly hardy and are still on their guard at this time of year. The gentle mild winter however has caused some plants to come to life earlier than normal. I have often observed how some plants seem to react euphorically to rising temperatures and wake up at the first mild weather. Others, wisely, reliably go by the calendar, working with daylength, and do not move until the time is right. Do not panic when in the morning you notice your tender peony shoots hanging limp. Wait for the air to warm up and the frost to go. You may well find the plant picks as if nothing happened.
Watering tip for the weekend
Please check the humidity in your soil: you may have to water. Especially evergreens such as rhododendrons and bamboo need watering. Although we had a very wet February, the past weeks have been dry and sunny, and there have been drying winds. This is the time of year where trees start pumping up huge amounts of water. Listen at the trunk of birch trees: you can hear it!
Die Königliche Gartenakademie is still open: Monday to Saturday from 8 a.m. to 6 p.m. and Sunday from 12 a.m. to 6 p.m.