Rosemary is not completely hardy in our latitudes. In very severe winters, the popular kitchen herb can quickly suffer frost damage. If the rosemary is frostbitten, it can still be saved with the right measures.
- Make nail test
- cut frostbitten shoots
- prune only after flowering
- do not cut into old wood
The evergreen Mediterranean semi-shrub should not be missing in any herb bed. Rosemary (Salvia rosmarinus) is not only a popular seasoning herb in the kitchen, but is also valued as a medicinal plant. Originally it comes from the Mediterranean region. From this it is already evident that the semi-shrub can poorly tolerate cold temperatures. In this country, the culinary herb is very sensitive to frost. However, with proper winter protection rosemary can survive cold periods normal to -10 degrees without damage. After even lower temperatures, the shoots of rosemary may sometimes be frostbitten in the spring. The plants reach winter hardiness only in the third year of standing. This depends on the location and soil.
Note: Breeding has resulted in various particularly hardy varieties such as “Arp”, ” Veitshöchheim”, “Backnang”, “Bavaria” or “Heilsberg”. In a favorable location, these varieties can easily withstand temperatures down to at least -20 degrees.
Recognizing frost damage
The full extent of frost damage only becomes really visible in April. More or less brown needle leaves are then visible. If only a few brown colored needles appear, it is not a cause for concern. This is normal. As a rule, nothing needs to be done here. The new shoots will overgrow this needle. However, if necessary, they can be easily stripped by hand. However, it becomes more problematic if several shoots are brown in color. This may be a sign that the rosemary is frostbitten. If this affects the entire plant, it is usually almost impossible to save.
Make nail test
With the help of a so-called nail test, it is very easy to determine whether the rosemary is really frostbitten. The procedure is very simple and can be done without any tools:
- lightly scrape the bark off the shoot with a fingernail
- alternatively use secateurs or knife
- If a slight green color appears, then there is still life in the shoot. Further measures can now be taken to save the plant. However, if a brown coloration of the shoot becomes visible under bark, then it is frostbitten. If the whole plant is affected, you can dispose of it.
Pruning the frostbitten shoots stimulates new shoots in the evergreen half-shrub. However, it should not be done immediately in April, because here the rosemary has already started to bloom. Therefore, with the cutting should wait until after flowering. Normally, by the end of May, the flowering period is over. Incidentally, late frosts are no longer to be expected. Other reasons for cutting at the end of May are
- Plant sprouts properly
- young, green shoots are easily recognizable
- Intersections close more quickly
- Fungal diseases have no entry point
- then grows nice and bushy
- Use scissors carefully
For pruning must be used clean and sharp secateurs. It should not be cut then also simply on it loose. There are a few things to keep in mind in order not to harm the plant even more:
- Do not cut into the old wood
- otherwise it will not sprout again
- remove only brown and thin tips
- shorten the shoot to the first green needle leaves
- leave 1 cm of the previous year’s wood on the shoot
Prevent frost damage
Already when planting rosemary, freezing of the plant in very cold winters can be prevented. In addition, there are also other measures to bring the semi-shrub well through the cold season, such as
- planting hardy varieties
- choose a warm, sunny location protected from cold northeast winds
- make sure the soil is well-drained (waterlogging in winter is often the cause of frostbite)
- always plant in spring (enough time for rooting)
- regular pruning after flowering (new shoots provide better winter protection)
- last harvest in October (better maturation of the wood)
- winter protection important
- spread layer of leaves around plants
- cover everything with spruce brushwood
- remove in spring
- overwinter potted plants indoors in a bright and frost-free place
Normally, night frosts can still occur until the Ice Saints in mid-May. Until then, the plants need protection. They should be covered with a fleece at night during this period.
Note: In an optimal location, the sun comes out in winter only from noon. This allows the plant to warm up slowly and prevents the plant cells from bursting open due to large temperature differences.
Frequently asked questions
Can rosemary still be harvested in winter?
If possible, no more shoots should be harvested from outdoor plants. The situation is different for potted plants in the house. Here, if necessary, some shoots can be cut.
What kind of soil does the Mediterranean evergreen half shrub prefer?
The soil should be well-drained, loose and lean, sandy if possible. The half shrub likes a neutral to alkaline pH. It is tolerant of lime. Heavy, clayey soils are not suitable for cultivation.
What care does Salvia rosmarinus need to grow?
Normally, the plant is quite undemanding. A small fertilizer application of compost or horn shavings in the spring is sufficient for garden plantings. These also only need watering on very hot days. Potted plants, on the other hand, need a dose of fertilizer every six weeks, in the form of liquid fertilizer. Watering is done when the top layer of soil has dried.