As tomatoes are perennial in their native environment, with a little know-how, they can be overwintered here too. Read below to find out how to keep your tomato plants in winter.
As soon as temperatures begin to drop, many gardeners ask themselves whether it’s possible to overwinter tomatoes. Here is a guide to how overwintering tomatoes works with tips on how to go about it.
Are tomato plants perennial?
The tomato plant (Solanum lycopersicum) originates from South America, where the wild shrubs are perennial and even relatively cold tolerant. However, it is a slightly different story for our cultivated tomato varieties, which have been bred for yield. These tomatoes are extremely heat-dependent, grow vertically instead of bushy and woody, and are very sensitive to the cold. In short, none of our tomato varieties are hardy in our temperate regions and cold winters. Temperatures below 10°C harm tomato plants, causing leaves to die, and deficiency symptoms such as the purpling of leaves due to a lack of phosphorus.
Perennial tomato plants can however be kept alive, by moving them to a temperature-controlled location that is as bright and warm as possible. However there is another good reason that these sun-loving plants are usually sown every year anew: often by the end of the season in October and November tomato diseases, such as late blight (Phytophthora infestans), ravage the plants. Only completely healthy and well-nourished plants can be successfully overwintered.
On top of that, it is essential to choose the right variety for overwintering tomatoes. Small, determinate tomatoes and wild tomatoes, on the one hand, can be wintered well as a whole plant. When moving them into their winter home, cut about half of the plant back, to adjust it to the lower evaporation and light requirements of the darker, cooler winter season. But don’t worry: plenty of new side shoots will form over winter, which will in turn bear flowers and fruit in the summer.
Indeterminate tomatoes, on the other hand, cannot be wintered as a whole plant. For these varieties, take cuttings from the plant’s shoot-tips. Although overwintering tomatoes is more time-consuming than sowing new tomato seeds, with the right light, water supply and temperature, it is just as effective.
Summary: How to overwinter tomatoes
- Most tomato varieties are perennial and can be overwintered
- When overwintering, make sure the tomato plant is completely healthy
- Wintering only works in warm, very bright locations
- Only determinate varieties can be overwintered as whole plants, whereas indeterminate plants must be overwintered as cuttings
- When overwintering, tomato plants may flower, but these should be removed because the fruits cost the plant too much energy
Why can you not harvest tomatoes in winter?
For supermarkets, tomatoes are produced year-round in high-tech heated greenhouses with artificial lighting. In fact, tomato plants do not know hibernation; in a suitable space, they will continue to blossom and fruit without rest. This sort of production is only worthwhile in warm countries with mild winters because it takes less extra energy to heat greenhouses there. In colder climates such as ours, good growing conditions for tomatoes in winter are hard to achieve without wasting a huge amount of energy.
How to overwinter tomatoes in containers
Generally, more robust wild tomato varieties take better to overwintering. We recommend varieties such as Humboldt tomatoes (Solanum humboldtii) or currant tomatoes (Solanum pimpinellifolium). The densely branched and small-growing determinate bush tomatoes such as ‘Tiny Tim’ or ‘Vilma’ are also suitable for this purpose. To overwinter whole plants in pots, they should also have been previously cultivated as potted plants, as the tomatoes will not survive transplanting from a bed into a pot. Wild tomatoes can be cut back by half before overwintering because they will produce plenty of new shoots in the following spring and bear fruit abundantly. Bush tomato varieties should not be pruned at all before winter.
Place potted tomato plants in the brightest possible place at 15 to 20°C from mid to late October. Before overwintering your tomatoes, make sure they are well-nourished and healthy plants. A final fertilisation in August and September before moving the plants to their winter location ensures they have all the nutrients they need. Only very bright locations are suitable, such as a conservatory. At south-facing windows, a mirror can be placed behind the plants to improve the light. Heated greenhouses provide an ideal supply of light, although they are not recommended as they require so much energy.
Overwintered tomato plants have developed long shoots: what to do?
Some overwintering tomato plants will turn yellow and form lots of side shoots to compensate for the reduced light. Do not remove these shoots, but do check them regularly for pests, as they are more susceptible to infestations.
However, if your tomato plant forms extremely light, thin, and unstable shoots, this is a tell-tale sign of insufficient light. Of course, looking for a brighter location is the best way to solve this. Another possible solution is a special plant grow light, which, unlike normal lamps, offers a light spectrum tailored to plants. However, this type of overwintering is less environmentally friendly, even if energy saving LEDs are used.
A less energy intensive alternative is overwintering with cuttings, which will be further discussed below. During overwintering until planting out the following May, water sparingly in winter and regularly again from March onwards. Start fertilising again in the spring too.
Tip: Keep an eye out for possible pests or diseases throughout the overwintering period, but especially from February and March onwards. Take measures to control pests as quickly and efficiently as possible and dispose of infected plant parts or whole plants.
Overwintering tomato cuttings
A good and space-saving alternative to wintering whole tomato plants is using plant cuttings. Tomato offshoots are easier to overwinter than tomato plants because they are smaller and more likely to be content with a place on the windowsill. When in doubt, a small plant grow light will help give the cuttings enough light. To overwinter with cuttings, cut off shoot tips about 10 to 15 centimetres long from healthy and well-nourished plants and let them root at about 20°C in water or a moist growing medium, such as our Plantura Organic Herb & Seeding Compost. After about a week, the first new roots will appear and after transplanting into more nutrient-rich potting soil, cuttings should grow quickly. To prevent the plants from growing too much, use a slow-release fertiliser such as our Plantura Tomato Food. In general, fertilise sparingly during the winter.
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It is important to check tomato cuttings regularly for pests and diseases too. From mid-May onwards, you can move the plants outdoors again, where they will bear fruit early thanks to their head start in growth.
By comparison, overwintering physalis is much easier than overwintering tomatoes. The edible flower can survive the cold season indoors and bear fruit early the following year.