After a cold winter in the garden or in a pot on the balcony rosemary often looks anything but beautiful green. In April, it becomes apparent what frost damage the evergreen leaves have suffered. If it is only a few brown leaves between the linear leaf clusters, you do not have to do anything. The fresh shoots will overgrow the dead leaves. Or you can lightly comb out the scrawny needle leaves by hand. If the rosemary looks frostbitten, you need to find out if it is really dead.
Rosemary frostbitten? When pruning is worthwhile
If you find yourself standing in front of a pile of scrawny-brown leaf needles from rosemary after a cold winter, you may wonder: Is it even still alive? If the rosemary appears to be frostbitten, then do the acid test: If the shoots are still green, pruning will help your rosemary look good again quickly.
What to do if the rosemary seems frostbitten?
To save the plants, do the “nail test”. To do this, scrape the bark from a small branch with your fingernail. If it still shimmers green, the rosemary has survived. Then it helps to cut the rosemary.
Tip: Wait with the pruning until it has faded and begins to sprout, this is usually the case in mid-May. Then you will not only see the young, juicy green shoots better, but the cuttings also heal faster and do not provide an entry point for fungal diseases. In addition, the danger of late frosts is over.
Cut with pruning shears as deep as you can see green. For example, if only the tips of rosemary are brown and scrawny, cut the shoot back to the first green needle leaves. As a rule of thumb, when pruning, cut back to within a centimeter of fresh green above the woody stems. Do not go deeper into the old wood. If the wood is dead, rosemary will not sprout. Rosemary does not have reserve buds, such as lavender, from which it could resprout if cut deeply.
If all the leaves are brown and scrawny, pruning the woody half-shrub therefore makes no sense. In that case, you’d better replant.
How to prevent frost damage to rosemary?
Plant out only hardy varieties in the open ground. Of the evergreen shrubs from the Mediterranean region, there are already some hardy rosemary selections, such as ‘Arp’, ‘Veitshöchheim’, ‘Heilsberg’, ‘Backnang’ or the new ‘Bavaria’. They tolerate temperatures down to -20 °C / -4 °F in a favorable location. And favorable means: a warm place protected from cold ninds, both in the garden and on the terrace or balcony. Rosemary loves sunny places. However, if the site is in the full sun from the morning in the first four months of the year, it can be dangerous. Rosemary belongs to the early bloomers. So the cells are already bulging, while other half-shrubs are still in winter rest. If there are then strong night frosts and the sun heats up in the morning, the cells burst due to the extreme temperature differences. A better location is one where the sun does not shine until midday in the winter months. This way the rosemary warms up slowly. Alternatively, shade your rosemary when the ground is frozen and the sun is shining.
This also helps against the so-called frost drought. Commonly spoken that the rosemary is frostbitten. In fact, the evergreen half-shrub dries up. Especially during longer periods of night frost in spring it becomes critical. In sunshine, the active green needle leaves of rosemary evaporate a lot of water, while the roots can not draw water from the frozen ground. You must continue to be on guard until the last frosts. If night frosts are forecasted, cover the rosemary with fleece again. It also helps to mulch the root area.
Winter protection is important. However, often it is not the freezing temperatures at all that are to blame for the rosemary looking frostbitten, but winter dampness. Therefore, you should properly winterize rosemary and provide well-drained soil. The greatest danger for the Mediterranean plant comes from waterlogging. Especially with older, very woody specimens, the lack of oxygen in a waterlogged soil causes the rosemary to look frostbitten and die.
Against the lignification of the plant helps regular pruning immediately after flowering, cutting off about a third of the previous year’s growth. Rosemary forms fresh shoots, which provide better winter protection. Complete the harvest of rosemary in the summer, so that the semi-shrub can mature and fresh shoots do not provide a target for frost. One or two shoots for the kitchen even in the winter months are no problem. Large quantities should not be.
And also by planting in the spring you reduce the risk that after the winter rosemary is frozen. Rosemary should be planted outdoors by mid-June at the latest, so that it roots well. Otherwise, the first winter overwinter the spice plant, which is also popular in the tub, bright and frost-free.