Strawberries are perennial and can be successfully overwintered. In order to prepare the plants for winter it is recommended to prune them.
Strawberries (Fragaria) should ideally stay in the same garden bed for three years. In order for the plants to produce good harvests in these three years, they have to survive the winters unharmed. Because the flowers of the strawberries are already forming in autumn, overwintering has a great influence on the crops of the following season. The so-called once-bearing strawberry varieties are also overwintered. The term ‘once-bearing’ indicates that there is only one harvest per season.
Pruning strawberries in preparation for winter
Freshly planted strawberries should not be cut in autumn. For plants that have already borne fruit, the leaves should be disposed of for phytosanitary reasons. This important pre-winter measure is used to remove the leaves that have not yet been affected by visible fungal diseases as a precaution to prevent further spread of the fungi. This should take place as soon as possible after harvesting (at the latest by mid/end of July). In the case of late-bearing varieties, the leaves must not be removed. The remaining vegetation period after the harvest is too short for new leaves and flowers to form. Therefore, a cut after mid-July would have a negative effect on the flowering and the harvest in the following year.
When removing the leaves, make sure that the new inner leaves remain undamaged. If this is guaranteed, cutting can also be carried out with a lawn mower (with as high a setting as possible) or a brush cutter. The cut leaves should be removed and not let to sit as mulch on the strawberry bed, because the fungi can survive on the dead leaves and the cut would have been for nothing. If you have a good and warm compost pile, you can put the leaves there. In addition to the leaves, all superfluous tendrils and runners should also be removed. After pruning, the plant stubble is covered around with some fertiliser in form of mature compost (leave the new inner leaves free). The plants will grow through the compost layer and have sufficient nutrients for flowering.
Summary of pruning strawberries:
- Remove the leaves of the strawberry plants after harvesting or by mid/end of July at the latest
- All plants that have a late harvest should not be cut
- Do not damage new leaves during pruning
- Do not leave the removed leaves in the garden bed as mulch
In the year when the strawberries are planted they are still small and vulnerable. In order to give them a fair chance to grow well and survive the winter successfully, they should be planted by mid-August at the latest. Both the roots and the flowers of the strawberry plants must be protected from frost. The roots are not very deep and therefore not very well isolated. The flowers are particularly sensitive in spring and because of that they should be protected from any late occurring frosts.
Overwintering strawberries in a pot
Keeping strawberries in pots or containers has one definite advantage – they can be moved easily. During winter, potted strawberries should be in a sheltered place, at best close to a house wall and on an insulating material (wood or polystyrene). In areas with milder winters, these precautions should be enough for the strawberries. If your garden happens to be in a colder climate or you just want to play it safe with your strawberry plants, cover your plants with brushwood, straw or fleece, for example. However, straw should not lay over the whole plant, as this creates a humid microclimate that attracts fungi. It is therefore best to place the straw only around the plants.
Brushwood is more permeable to air and can therefore be draped over the whole plant. Fleece can also be laid over the plants because it does not prevent air and moisture exchange. If the strawberry plants are placed under a protective cover, don’t forget to water them a little on frost-free days. But be careful: do not water the strawberries too much or let the water in the soil freeze because this would severely damage the roots.
Overwintering strawberries in the garden bed
Strawberries in garden beds are less protected compared to their potted counterparts. They should therefore be planted in beds that are not excessively exposed to the harsh elements such as wind and cold. Since waterlogging in winter can lead to considerable frost damage to the roots, choose the location carefully and prepare the soil cautiously. In gardens that do not offer many alternative locations and are at risk of waterlogging due to loamy soil, it can be helpful to mix some sand with the soil to provide better soil drainage.
Planting on raised beds (approx. 40 cm in height) is also a possible way to overwinter strawberries in poor soil locations without the water-related damage. Depending on the region, the strawberry plants in the garden bed should be covered in the same way as those in the pot. Cover the plants around with straw or with brushwood or fleece over the whole plant. It is important not to remove the frost protection too early in spring. Otherwise, a sudden return of the colder weather or unexpected late frosts can cause serious damage to the flowers. A black pistil is a typical symptom of a damaged frozen flower. Unfortunately, in this case it will no longer bear fruit.
Protecting strawberries from frost:
- Place pots and containers in sheltered places
- Do not forget to water pots in covered areas moderately on frost-free days
- Cover strawberry plants in pots or beds with fleece or brushwood in cool regions
- Straw is also suitable as insulation; do not place it onto the plants directly but on the ground around them
- Maintain frost protection until last late frost, strawberry blossoms are very sensitive in spring
If your strawberries survived winter successfully, in this article here you can learn how to ensure a plentiful strawberry harvest.