How to protect plants from frost
The first frost will soon be upon us and some plants will need protecting. There are many ways to protect the plants, whether you use winter protection tents, frost protection fleece or coconut mats.
Frost can damage sensitive plants, so it is best to take precautions as soon as the weather forecast predicts freezing temperatures overnight. Prepare for frost by following our tips on how to protect your garden and plants from frost.
- Which plants need protecting from frost?
- At what temperature should plants be covered?
- How to protect plants from frost
- How to fertilise frost-hardy plants correctly
- Creating a mulch mound
Which plants need protecting from frost?
Not every plant needs to be protected from low temperatures, but frost protection is especially important for sensitive plants, for example:
- Plants in pots and tubs, balcony plants
- Young plants, both vegetables and young woody plants
- Frost-sensitive vegetable plants that are to be harvested over a longer period of time
- Plants pre-cultivated in a greenhouse and bought from a garden centre in autumn or spring
- Tropical houseplants
- Fruit trees in spring (because late frost can damage the blossoms)
- Lawns (because some grasses are less hardy than others)
- Plants with a winter hardiness rating of H1 to H4
Tip: Not all plants need protecting from frost. Different plants have different overwintering strategies.
Tip: When it comes to frost protection, familiarise yourself with your region’s winter hardiness zone and the plant’s winter hardiness rating. The winter hardiness zone refers to a geographical area that encompasses a specific range of climatic conditions that are essential for plant growth and survival. Always protect plants with a hardiness rating of H3 and lower.
At what temperature should plants be covered?
The temperature at which plants should be covered varies according to the season and the plant’s characteristics. Plants that are very hardy may not need any additional frost protection. Some, on the other hand, are vulnerable to frost damage between autumn and spring and others only in spring. Because not all plants are equally frost-hardy, always tailor your frost protection to the situation.
Tip: Plants bought from a garden centre in spring or autumn that are usually winter hardy, often fall victim to frosts as they are not acclimatised to colder temperatures. They are used to warm pre-cultivation temperatures and need to be protected as a precaution.
Protecting plants from frost in autumn and winter
Autumn marks the beginning of the frost protection season. Keep an eye on the weather forecast and the temperature. The first frosts of the season usually occur on clear, windless nights – make sure you have frost protection measures in place by then.
- Plants can also dry out in winter. Make sure to water them regularly when the soil has thawed but avoid waterlogging.
- In the event of prolonged frost and winter sun, evergreen shrubs, roses and heat-loving woody plants must be protected. Cover the plants with air-permeable materials only, such as frost protection fleece or jute.
- Winter vegetables will not be damaged by the cold, but you can still cover them so that you can continue to harvest them without problems despite the snow.
- When overwintering pot and balcony plants, it is important to remember that overwintering them too warmly harms many pot plants. Therefore, find out for each plant what overwintering conditions it needs.
- Cover plants with winter hardiness rating of H1-H3.
- To prevent frost-drying, add a layer of mulch around the plant and water on frost-free days. Frost drought leads to water deficiency in plants because the leaves transpire water but are unable to absorb new water due to frozen soil and eventually wither. Shallow-rooted plants, such as rhododendrons, are especially vulnerable. This is due to the fact that their roots do not penetrate deep into the soil, where plant-available water can be found.
- Create a mound of mulch, leaves or soil around roses to protect the crown.
- Protect the lawn by giving it a potassium-rich fertiliser in autumn. Potassium increases the plants’ resistance and makes them strong for the cold season. Special autumn fertilisers with a long-lasting effect are particularly suitable for this. Perennial plants benefit from autumn lawn fertilisers as well as it helps them to withstand dry, cold periods better.
Protecting plants from frost in spring
Plants should be protected from frost in spring until the Ice Saints (12th to 15th May) because night frosts are possible until then.
- Cover your plants at night until mid-May using a horticultural fleece for example.
- Keep pot plants inside overnight until mid-May.
- Protect the blossoms of fruit trees from late frost – frost protection candles are a good way to do this.
- Keep a close eye on the daily weather forecast. If temperatures are expected to drop again after warmer periods, it is important to protect the plants from frost.
Tip: Even if spring plants are sold in the garden centre before mid-May, it is best to wait until after this date to plant them in beds or protect them from frost until then.
How to protect plants from frost
There are various options to choose from for protecting plants from frost. They are made of various materials and can be used in a variety of ways. Did you know that snow provides natural frost protection for plants? It has an insulating effect, just like many of the materials we discuss here:
Winter protection tents for plants
Winter protection tents are made of plastic film and can be used to store plants over the winter. If it gets particularly cold, a plant heater or frost candles can be used to add heat to the tents. These tents are ideal for outdoor potted plants that are hardy but may require protection in extreme cold. They can also be used to effectively pre-cultivate young plants in the spring. The tents come in a variety of sizes, are translucent, and can be reused; however, they are quite expensive.
Frost protection with horticultural fleece
Crop covers or horticultural fleeces are made of a thin plastic material that is permeable to both water and air. As a result of soil moisture evaporation, a thin layer of ice forms beneath the fleece, preventing heat radiation from the soil. If you prefer a more natural material, you can have them made of sheep’s wool. These are biodegradable but not reusable. Thick construction fleece is also available. It insulates better and does not tear as easily, however, it is not translucent and plants that need sunlight in winter will need to be uncovered during the day.
Horticultural fleece is very versatile and can be used to protect vegetable crops as well as young plants. You can also use the horticultural fleece to insulate more frost-sensitive woody plants, by wrapping it around the plant and tying it tightly.
Frost protection with coconut mats
Coconut mats are made of a very durable material obtained from the coconut’s outer shell. They can be wrapped around plants or tubs in a similar way to horticultural fleece. As a regional alternative, you can use mats made of hemp. These are more durable than garden fleece, but they are not translucent and usually cost more.
Fir branches for frost protection
Branches from fir or spruce trees can also be used as a protection against frost. Wrap it around the grafting points of roses by bending it into a ball shape and tucking it in. This insulates the soil and while still allowing for ventilation, making it less damaging to the plant’s delicate parts. You can also use fir brushwood to cover shrubs that die back over the winter or pot plants. Laid flat on beds, its value is mainly decorative.
Mulch for protecting against frost
Mulching is recommended to protect the soil, as well as the roots and plants growing in it. Materials such as leaves, straw and bark mulch are used to retain heat and moisture in the soil. In addition, bark mulch protects garden soil from erosion and siltation. It also provides a sustainable supply of carbon for humus formation in the soil. Pine tree bark is particularly effective thanks to its longevity, low heavy metal contamination and low acid content.
Hessian for frost protection
Hessian, also known as jute, is a durable natural fibre used to make bags and cloth. It can be used in a similar way to horticultural fleece. Hessian sacks can be placed over the crowns of plants or plant pots. Do not wrap evergreen plants continuously over the winter, as jute is only slightly permeable to light. Hessian sacks have long been used to protect roses against frost. They come in a variety of colours, so you can add some exciting pops of colour to your garden in winter.
Bubble wrap for frost protection
Bubble wrap can be used for protecting against frost, as the air pockets create an insulating effect. Unfortunately, however, water and air exchange is not possible through the plastic, which means that the plants sprout too early and become more susceptible to frost and diseases. It is therefore recommended that you only use it around the pot, which also needs frost protection in winter. If you do want to protect plants directly with the film, you should only use it for short periods, such as during night frosts in spring, and make sure you ventilate regularly.
Frost protection candles are commonly used in fruit orchards in spring, when the risk of late frost can damage newly formed blossoms – April can be a very critical month. On evenings when temperatures are expected to drop below 0 °C, it is advisable to light the candles late in the evening. The worst of the cold usually passes by around 8 a.m. A temperature increase of up to 3 °C can be achieved by using one to two candles per every 20 square metres.
How to fertilise frost-hardy plants correctly
Come summer, start fertilising plants with potassium instead of nitrogen. Potassium is stored in the plant’s cell sap, which increases the salt content and in turn lowers the freezing point making the plant more winter hardy. Applying nitrogen-rich fertiliser in autumn will promote growth, making the plant sprout too early and consequently more susceptible to frost. Additionally, nitrogen-rich fertilisers contain ammonium which inhibits potassium uptake and is counterproductive to winter hardiness. It is still important to be aware that many potassium fertilisers contain chloride which many garden plants may react strongly to.
Creating a mulch mound
Protect perennials and the sensitive grafting points of woody plants in winter by covering them with a mound of soil or mulch. This is an important frost protection measure, especially at the grafting points of roses.
Not all plants should be protected from frost outside. For some, it is worth moving them directly to warmer winter quarters indoors. Find out what to look out for in our article on overwintering plants.