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Sweet William are considered to be hardy. Ideally, they will survive the cold season outside in the bed without any problems. In some cases, however, the romantic summer flowers need a little extra protection.

In a nutshell

  • in the garden bed, carnations are usually sufficiently hardy
  • Young and potted plants need some protection
  • never overwinter the flowers in warm indoor areas

growth cycle

Sweet William, botanically Dianthus barbatus, is a biennial plant that only sprout a rosette of leaves in the first year. Only in the second year do they also form flowers, only to die off after the seeds have been produced. The Sweet William must therefore survive the first winter in order to flower. Commercially available plants are already in their second year of life.

Diantus barbatus

hardiness zone

An important criterion by which one can estimate whether a plant is hardy is its natural distribution area. The Sweet William originally comes from the mountain regions in Eastern Europe to China. To survive here, the flowers must survive freezing frosts.

  • Hardiness zone: Z4 (not found in Germany)
  • Temperature minimum: -29 to -34 degrees Celsius

Notice: The classification according to winter hardiness zones only serves as a rough guideline when cultivating the plant in Central European regions.

For Central Europe there is a subdivision of the zones (Z) into semi-zones (a+b).


For winter hardiness, it is not just the overall climate that has to be taken into account, but above all the microclimate that is present in the specific case. If the Dianthus barbatus is close to the wall of the house or a few meters away in the same garden completely unprotected in an open area, that makes a significant difference. The factors responsible for the microclimate are manifold. In addition to the health of the plant and the specific soil conditions, the course of the weather is also of great importance. And not just in winter, but in the summer and autumn before that. In the home of the Sweet William, winters are regularly extremely cold and dry. In most cases, there is also a protective layer of snow for months. However, our winters are often mild and wet. Large amounts of water and winter waterlogging are therefore more difficult for flowers in this country than the cold. Strong temperature changes within a few days are also not ideal for the otherwise robust flowers.

Overwintering variants

Depending on whether the Sweet William is cultivated outdoors or in tubs, there are various options for ideal overwintering.

Hibernation in the bed

Sweet William planted and established in the garden bed in May usually get through the cold months without any special protection. Only very young carnations are not yet sufficiently hardy. It is therefore best to simply cover the ground above the plants a little. This not only protects the ground from freezing, but also from excessive moisture. A thick layer of organic, air-permeable material is sufficient for this. Preferably use:

  • straw
  • mulch
  • dry foliage
  • Fir or spruce branches

Hibernation in bucket

Overwintering the Sweet William in pots is a little more difficult, although not particularly complicated. Since the carnations are sufficiently hardy, they do not have to move to a frost-proof quarter. On the contrary: You should also leave them outside in winter. Bringing them into a warm house does more harm than good. Because if the temperatures are too high, the unusual flowers do not hibernate. However, they need this break in order to sprout vigorously and form flowers next year. It is therefore better to place the bucket in a protected place on a styrofoam plate or on wooden blocks and to wrap the container with fleece or sacking.

  • When: late October (before the first frosts)
  • Location: partially shaded
  • protected from wind and rain

care in winter

Carnation plants also need water in winter. However, you should not overdo it. Nevertheless, the roots must not dry out for a long time, even if there are no more leaves above the ground. It is important to regularly check the soil moisture, especially for potted plants that are placed in a rain-protected place.

Tip: Water only on frost-free days and in small quantities.

frequently asked Questions

Are there perennial sweet peas?

Usually, Sweet William flowers in the second year and then die off. With some specimens it is possible that they will also sprout and flower in the third year. Therefore, in the second year, do not dig up and dispose of the plant, just cover it with some brushwood. With a bit of luck, the flower will sprout again next spring. Otherwise, it provides for offspring at least by self-sowing.

Do I have to prune the Sweet William before winter?

You can, but do not have to, cut back the carnation plant in the fall. With mild temperatures, the plant keeps its green foliage even over the winter. If necessary, you can also remove dead shoots in the spring. If you do not want the flowers to sow themselves, you should remove the inflorescences with the seed pods by autumn at the latest.

Can you overwinter the flowers in the dark?

In general, the Sweet William should preferably be brought over the winter in a bright location, as it keeps its foliage in mild temperatures. However, if the above-ground shoots died in autumn, you can safely overwinter the plant in the dark without damaging it. However, keep in mind that the location must not be too warm. A sheltered carport or cool garage is ideal for this.

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