Strawberries are important to thousands of home gardeners every yeara delicious treat. They are among the fruits that are harvested in practically all countries in the temperate zone and their growth cycle promises a good harvest. As a rule, the strawberry plants are awakened from their long hibernation by rising temperatures before the start of spring and grow quickly to provide the gardener who has cared for them with aromatic fruit. But in most regions, the cold winter poses a real threat to perennials. In this article you will learn how you can overwinter strawberries so that you can look forward to aromatic fruits in early summer.
The growth cycle of a strawberry plant
Strawberries are perennial, fast-growing shrubs. They set flower buds in autumn. The plant then needs a long period of rest to use photosynthesis at lower temperatures and less intense light to build up sugar in its stems and runners, which ensures fruit set the next year.
In strawberry plants, dormancy does not mean that it is completely inactive, but that the plant is redirecting its energy to form buds for fruiting or runners for daughter plants.
If a strawberry never gets that rest it needs to recharge, it will continue to try to bloom and bear fruit. But it will grow weaker and weaker and produce fewer and fewer strawberries, while the leaves and roots become more and more susceptible to disease.
Which strawberries can you overwinter?
Everbearing varieties such as Albion, Camara and Mara des Bois, also called day-neutral strawberries, can bear fruit from July to October, but the plants will only become weaker if not overwintered properly.
If the strawberry bears most of its fruit in early summer, i.e. May - June, it is also a good candidate for overwintering. These June-bearing strawberries need winter care to boost production next year. Strawberry varieties of this type include Lambada, Honeoye, Malwina, 'Senga ® Sengana' ®, Mieze Schnindler and many others. We cannot list all early ripening varieties here. But they were probably marked as such when purchased. Check with the breeder or nursery to be sure. Winter care for strawberries begins in late summer.
Cut back strawberries and prepare them for winter
Late summer or early fall is the best time to “rejuvenate” strawberry plants. If you see that your strawberry plants are not producing new fruit, it is time to prepare them for winter. The strawberry plants are cut back to a height of 5 cm. This interrupts disease processes and denies insects a winter quarters.
If you have a small strawberry patch or grow your strawberries in containers, you can prune them with hedge trimmers. If you have a large, flat bed, you can use a lawn mower, but you must make sure the blade is raised to keep the crown of the plant intact. You can use any plant remainsput on the compost.
At the end of summer you can fertilize your strawberry plants in the bed with all-purpose fertilizer (NPK 10:10:10). The usual amount is 450 grams per 25 plants. Spread the fertilizer balls over the soil, rake them in gently and water the plants (preferably using a drip system). You can also use compost or foliar sprays with mineral components.
In any case, you should fertilize the strawberries in late summer or early fall, at least a month before the expected first frost. What's important is that the stems and flower buds have a chance to ripen before the really cold weather sets in.
How to overwinter strawberries
Overwinter strawberry plants in beds/raised beds
A few light frosts are enough to send your strawberry plants into winter dormancy. However, winter temperatures well below -10 degrees kill the flower buds that the plant needs to produce fruit next year. That's why it's important to protect the flower buds from the winter cold.
Strawberries are relatively small plants, but they have great yielding power. Due to their small size and easy adaptability, they are ideal as bedding and container plants. How to overwinter strawberries in a container is covered in the next section. Here we will briefly discuss the basics of overwintering strawberry plants in the bed.
Overwintering strawberries in the bed is relatively easy. Strawberries are mostly cold-resistant and can survive even light frosts without any problems. Therefore, in areas with mild winters, little to no maintenance is required. However, in more northern regions, cold protection in the form of mulch is required.
It is essential to protect strawberry plants when the temperature drops below 20 degrees. Once this temperature is reached (usually in January or February), the plants should be in the dormant phase. Then it's time for herto overwinter by mulching. In most regions, a mulch layer of straw or pine needles two to three centimeters thick is sufficient.
An important principle of cold protection is that air is a good insulator. The secret to keeping strawberries warm in winter is a thick covering or light layer of mulch that traps warm air. It would be even better if this mulch had many surfaces that can catch moisture droplets that give off heat when they freeze.
Pine needles make an excellent mulching material. They are easy to rake off strawberry plants as the weather warms in spring, and they keep the soil slightly acidic as they rot. Clean, weed-free wheat, oat or soy straw are also good choices.
Covering your plants with plastic wrap will increase the overall temperature underneath as long as the edges are sealed. The warmth of the soil helps maintain temperature because the subsoil freezes less quickly than the topsoil, air or water.
Cardboard is sturdy and can be suitable if you want to cover a small strawberry patch or pot. It blocks the wind and increases the temperature underneath.
It is important to harden off your strawberry plants through a few light frosts before applying a protective layer of mulch.
Overwinter strawberry plants in pots
When overwintering strawberry plants in pots, the principle applies that the shoots are hardy, but the roots are sensitive. Strawberries grown in containers benefit from winter protection. Most planters for strawberry plants are not particularly well insulated. The planting substrate inside the container can become just as cold as the surrounding air. If a shoot dies, the plant can replace it. But if the roots freeze, the plant dies too.
The key to overwintering is controlling the temperature so the plant is alive but not actively growing. By slowly exposing it to lower and lower temperatures, the strawberry plant can produce its own “antifreeze.” Sugar accumulates in the plant sap in the stems and roots, which prevents the plant from freezing. Constant freezing and thawing causes the plant to produce new shoots that die off with the next frost, leaving it weaker next spring.
Successful wintering requires good timing. Strawberry plants should sit in their pots for several weeks before being exposed to the cold. In most colder areas of Germany, this means that annual plants have to be in pots in their winter quarters as early as October so that they are ready for the cold in November. The stronger the root system, the stronger the plant.
Dead stems and leaves should be removed in a timely manner to avoid botrytis infections.
One of the best ways to overwinter strawberries on the balcony is to place the bucket in a larger container and insulate the space with leaves, straw or Styrofoam chips. Alternatively, you can wrap the entire bucket with an air-permeable insulating material. You can also place the container on the floor next to a heated wall. The location should ideally be protected from wind.
By the way, winter can be the best time for growing strawberry plants. You can plant annual plants in containers in early fall and place the container in a sunny but protected place. The plant can set flower buds and form roots to grow magnificently next spring.
Another option is to overwinter the pot in an unheated garden shed, cellar or garage. Don't worry about the lack of light. The plants are in the dormant phase and do not need any light in winter. You'll probably only need to add a little water every few weeks to keep the roots from becoming too dry. Outside, melting snow and occasional cold rains usually keep the roots moist enough through the winter without you having to water them.
The only overwintering method that is not recommended is to place the strawberries in the apartment or a heated room and try to grow them as a houseplant. This is fine for some tropical plants, but strawberries need winter dormancy to have strength for next year's fruit production.
Hydroponic strawberries overwinter
Overwintering hydroponic strawberry plants is more difficult than overwintering those in beds or containers because they are grown in water. Water is not a good insulator and freezes in cold temperatures. However, hydroponic strawberry plants can be overwintered in sand. If you store the strawberries in their hydroponic mesh pots and overwinter those pots with the roots hanging out, you can successfully keep them alive in a sandbox in the garage. However, you must make sure that the roots are completely covered by sand and that the sand does not dry out. As long as the sand stays moist and the temperature in the garage doesn't reach arctic cold, they should be fine. Also be sure to use sterile sand when overwintering strawberry plants. Otherwise, it can contain all sorts of pathogens that can spread to the plants and kill them during their stay in winter quarters.
What about overwintering strawberry plants in towers?
Strawberry towersare generally intended for only one growing season. The surface area exposed to cold air is too large. Winterizing with fleece makes little sense unless you live in a warm winter climate.
Should you water strawberry plants in winter?
Little water is required during the cold season and when the plant is dormant. For strawberry plants that are overwintered in beds with mulch, natural rainfall should ensure sufficient soil moisture. However, water must be provided for the potted plants. The easiest way is to collect snow from outside and throw a handful or two of it on the ground to provide enough water. The slightly warmer temperatures in the garage should slowly melt the snow so that the water can naturally seep into the soil of the potted plants. If you do this regularly (about once a month), the soil should be sufficiently moistened so that the plants can thrive again in the spring.
