Raised beds in winter: what to grow & how to deal with frost

Even in a raised bed, some plants can thrive and be harvested during the cold season. We explain how to prepare your raised bed for winter and which plants can be overwintered on a raised bed without any problems.

The popularity of raised beds as ornamental or vegetable beds has continued for years and they can be found in many gardens. In summer, raised beds can provide large yields of vegetables and herbs – ornamental flowers also thrive there. Winter, on the other hand, is the time for last-minute harvesting, as well as caring for and preparing the garden for the coming year. A few plants continue to grow slowly through the winter, and sowing seeds during this cold period conveniently ensures that spring vegetables will be ripe earlier. We explain how to use the raised bed in the winter, prepare it properly and protect it from the winter cold. Indeed, there are several ways to ensure that the raised bed does not lie fallow in the winter but still harbour some inhabitants.

Raised bed in winter: overwintering perennial plants

Perennial plants that are sufficiently hardy can simply be left in the raised bed over the winter. Various perennials survive the winter in the raised bed without damage. It is also possible to overwinter a number of herbs in the raised bed and some of them can be harvested even during the cold season. Herbs such as sage (Salvia), thyme (Thymus), and rosemary (Rosmarinus officinalis), which retain their leaves in winter, can then continue to add flavour in the kitchen. However, since in the cold season nothing grows back, harvesting should not be too rigorous. It is also advisable to harvest only individual leaves, as cutting off entire shoots would create entry points for frost and pathogens.

In general, when overwintering plants, you should pay attention to how much cold they can tolerate, if necessary providing additional protection so that you get the plants through the winter alive. You can read more about this a little further down, where we describe a protective cover for the raised bed.

Growing winter vegetables in a raised bed

Even in raised beds with winter protection, (almost) nothing can be sown at the cold time of year to grow through the winter: light and heat are lacking for most vegetable plants to germinate during the cold season. Nevertheless, there are many vegetables that can be sown in the summer or early autumn and then simply left on the bed throughout the winter. If the sun shines for a few days, these winter vegetables in the raised bed will continue to grow very slowly. They also stay fresh much longer and take up less space than if they were harvested and stored earlier.

Tip: Frost-tolerant winter vegetables are usually leafy and cabbage vegetables. When harvesting, you should pay attention to the following: if the plant is to sprout again after harvesting, it should only be harvested on frost-free days. This ensures that the plant is not damaged by excessively low temperatures and it can then be harvested again after a few weeks.

• Field lettuce: In some places, lamb’s lettuce (Valerianella locusta), is already called winter lettuce – frosty temperatures cannot harm it, in fact the cold even improves its taste. During the cold season, however, it takes a long time to grow, which is why it is a good idea to cultivate lamb’s lettuce indoors. If sown in September or October, lamb’s lettuce can be harvested from November to December. For even later sowings, be sure to use a frost-resistant variety such as ‘Vit’ or ‘Verte de Cambrai.’ Depending on weather conditions, these can easily be harvested well into March of the following year. A special feature of lamb’s lettuce is its ability to regenerate: if you cut off only the upper leaves and leave the roots and the base of the plant undamaged, it will regenerate and can be reliably harvested again in a few weeks.
• Endives: Like lamb’s lettuce, Endive lettuce (Cichorium endivia) is also a leafy vegetable that has some frost tolerance. At temperatures down to –5 °C endives do not bear any damage, so they are well suited for planting on the raised bed in winter. If the endive is sown by the end of August, it will still be ready for harvesting in November and December. This involves cutting off the entire head of lettuce just above the leaf rosette – allowing the individual endive plants to be harvested one by one.
• Kale: Kale (Brassica oleracea var. sabellica) is a well-known selection of cabbage and very closely related to Brussels sprouts (Brassica oleracea var. gemmifera), Kohlrabi (Brassica oleracea var. gongylodes) and others. Depending on the region, it is also known as leaf cabbage. In order to enjoy the characteristic aroma, kale is harvested only after the first frosts. Temperatures down to -10°C pose no danger to it. This winter cabbage must be grown from early summer to enjoy it during the cold season, as it takes up to six months from planting to reach maturity. Between November and January is the peak season of kale: during this period, the kale can be harvested continuously. If you want to enjoy a lot of kale despite a small raised bed, you can use an old trick: if you carefully strip off the individual leaves when harvesting and leave the stalk, the kale can sprout again in mild weather and then be harvested again.

• Parsnips: For parsnips (Pastinaca sativa), the garden year starts with sowing in early spring. Harvesting can begin from about September. However, you can harvest the root vegetables throughout the winter as needed and use them fresh: since the delicious roots are protected from frost by the soil, they can easily remain in the bed and always be harvested only when they are needed.
• Winter spinach: Spinach (Spinacia oleracea) is one of the plants that should not be missing in your winter garden. To grow spinach in a raised bed for the winter, it should be sown directly in the raised bed between mid-September and mid-October. For this purpose, we recommend opting for very frost-resistant and fast-growing spinach varieties such as ‘Matador’ or ‘Redbor’. From mid to late November, the plants are then ready for harvesting. If you only carefully harvest individual leaves from the spinach, it can sprout again in mild temperatures and thus be enjoyed several times. The last harvest of winter spinach typically takes place in early April.
• Welsh onion: The name Welsh onion is actually just another name for the universally known spring onion (Allium fistulosum). This plant in the onion family is very hardy. It can still be sown in early autumn and harvested throughout the winter. But beware: if you really want to enjoy the perennial Welsh onion, do not pull out the entire plant from the ground, including the bulb but only cut off the green – similar to chives.

• Purslane: A real insider tip for winter in the raised bed is miner’s lettuce (Claytonia perfoliata), also known as Indian lettuce or winter purslane. Miner’s lettuce can be sown directly into the bed from September to October, in raised beds with cold frames even from September to March, as it germinates at a temperature of 4 to 12°C. When fully grown, Postelein is incredibly robust and frost-resistant, withstanding temperatures as low as -20°C. If the leaves are not cut too low, purslane can be reliably harvested several times. The fleshy leaves are wonderful as a fresh salad but can also be prepared like spinach.
• Wintercress: Also known as herb barbara, winter cress (Barbarea vulgaris), like winter purslane, is one of the few vegetable plants that are very robust against cold, germinating and growing even at low temperatures. Winter cress is one of the light germinators – its seeds are therefore not covered when sowing but only pressed and watered. To harvest in December, spinach is sown between September and October.

Preparing the raised bed for winter

It is also worth asking whether the raised bed itself should be prepared for a harsh winter in order to protect the material. Of course, this is not a disadvantage – and with a few simple steps you can even promote the growth of perennial plants and winter vegetables in the raised bed.

Wrapping raised beds in bubble wrap or garden fleece

As with potted plants, a raised bed can be wrapped in bubble wrap, garden fleece or jute. The additional protection keeps the cold out because the frosty temperatures can no longer penetrate so quickly into the root zone of the plants. In extreme sub-zero temperatures, this provides protection, and on warmer winter days this precaution may even encourage growth somewhat, as the heat is retained longer in the bed.

Covering raised beds in winter

Another natural way to protect the plants in winter is to cover the raised bed with leaves. Other mulch materials such as brushwood or fir branches are also suitable. This has the advantage that the soil and winter plants in the raised bed are protected and insulated from the cold. However, the layer of foliage should not be too thick or too close to the plants, otherwise moisture and rain will increase the risk of diseases such as stem rot. Vegetable plants that are heavy feeders can be isolated with a layer of compost or well-rotted manure.

In particular, rainy weather in the winter worries many garden lovers. The question quickly arises: Do I need to protect my raised bed from rain in winter? If the raised bed is not sufficiently well drained, that is, rainwater can not drain well, the answer is a resounding yes. However, even permeable beds can benefit from a proper roof to protect them from rain and cold wind: If hardy plants, such as certain types of vegetables and lettuce, are grown in winter, a cover can prolong the harvest period. This is because the bed stays warm longer with protection in autumn and warms up faster in spring.

The best option for rain protection is a cold frame attachment for the raised bed, as this allows enough light to reach the plants, can be ventilated if necessary and reliably keeps rain out. By the way, you can find out how to build a cold frame yourself in our dedicated article. Another practical solution is to stretch plastic sheeting over the raised bed to form a simple foil tunnel. Homemade covers made of double-wall sheets or lattice film for greenhouse construction are an option for DIY enthusiasts. The cost of materials is often low compared to the purchase of finished structures.

Whichever design you choose, always make sure that the plants do not touch the cover because mould is likely to develop where they come into contact with condensation. In addition, especially when growing vegetables, care should be taken to ensure that regular ventilation is possible to reduce humidity and thus the risk of fungal diseases. During heavy snowfalls, raised bed covers such as foil roofs and tall plants such as kale should be freed from the snow load to prevent damage to the structure or the plants themselves. Otherwise, snow itself is a wonderful insulator against freezing temperatures and can remain on the bed.

Tip: Mobile raised beds can be placed in a sheltered place in winter to improve growing conditions, or even in a frost-free, brightly lit porch, a half-closed garage, or a conservatory.

Preparing a raised bed for the next season

If you think ahead when caring for your raised bed, you can save yourself some work in the spring. If the high bed is completely cleared in autumn and has no winter greenery, the winter can be used wonderfully to prepare for the new season.

Mulching and new filling

Especially if the vegetable patch is subsided badly due to rotting processes, it is worth replenishing it in autumn and winter. To do this, remove all plant debris – including roots and weeds – from the raised bed and fill it with compostable material and mature compost. At the first frost, cover the raised bed with mulch material – for example, spruce and fir branches. The material will start to decompose over the winter.

Towards the beginning of April, when the weather warms up again, rid the raised bed of its mulch layer and fill it with a new layer of nutrient-rich potting soil, such as our peat-free Plantura Organic Tomato & Vegetable Compost. This top planting layer is not too rich in nutrients and therefore better for most vegetables than the compost or manure layer below. The compost layer serves mainly as a nutrient stock for the coming years. Prepared in this way, the first plants can soon move into the raised bed and enjoy the replenished supply of nutrients.

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Green manuring and pre-seeding

On the other hand, those who do not want to leave their raised bed empty in the winter do not have to give up caring for it. Adding green manure in autumn is an ideal way to do something good for your stressed raised bed. Before the first frosts sweep across the land, it is time to sow green manure crops such as winter vetch (Vicia villosa), crimson clover (Trifolium incarnatum), bee friend (Phacelia) or a mix of species. They not only look decorative in the raised bed but also improve the soil structure and protect it from the weather. In addition, these plants loosen the soil with their roots and, if legume plants such as vetch and clover are present, fix atmospheric nitrogen. This later serves as fertiliser for any vegetables planted.

In parallel or instead of green manure, it is possible to sow the first seeds in the late autumn and winter, which should germinate in the spring: Early radish (Raphanus sativus var. sativus), carrots (Daucus carota), beetroot (Chaerophyllum bulbosum), head and cut lettuce (Lactuca sativa), and herbs such as chervil (Anthriscus cerefolium), borage (Borago) or parsley (Petroselinum crispum) may be sown in October or November instead of spring. If you also cover them with a thin layer of mulch and a cold frame, they will survive the winter there and often germinate much earlier than plants sown in March when temperatures begin to rise.