Winterising plants | The 3 main methods

overwintering frozen plant sunflower snow

Winterising plants is by no means an easy discipline. But it is absolutely necessary to learn if you dream of having, caring for, nurturing and harvesting from the same plant for more than one season at a time.

Overwintering is necessary for many outdoor plants, but not all of them. Many local plants, i.e. plants that originate in Denmark and the Nordic countries, can easily go into "hibernation" and survive the winter on their own, this is called natural-wintering. However, most "exotic" plants are not able to survive a winter in the harsh Danish environment. Therefore, it is important to learn how to overwinter them.

When we talk about "exotic plants" in the context of overwintering plants, it's not quite the same degree of exotic that is usually referred to. This includes everything from basil and cucumbers to tomatoes and lemon/olive trees.

These are all plants that are not suitable for the Danish weather and winter. But with a little unnatural help from us humans, they can of course survive the winter so you can enjoy them again next year.

The 3 types of "artificial" plant overwintering

Before you start overwintering all your plants, it's important to be aware of the different types of overwintering and their differences, and of course, to think about what type of overwintering you're looking for. In general, there are three different types, all of which are different and all strive for different results.
  • Overwintering with survival
  • Overwintering with growth
  • Overwintering with growth and fruiting

In many ways, the different types of overwintering can be seen as different levels of the same thing. The primary purpose of all types of overwintering is to overwinter the plant, keeping it alive and ensuring it survives the winter. The differences between the different methods then centre around "how well" the plant survives.

The benefits of overwintering your plants are numerous. Firstly, you don't have to buy new plant seeds over and over again, every single year. Secondly, you can grow your plants significantly larger as they can be allowed to grow for much longer than they would otherwise.

That's why we think overwintering plants is a great idea if you want to challenge your plant growing skills a little. It's also quite satisfying when you successfully overwinter a plant for a whole winter for the first time.

Full spectrum grow lights for tomato plants indoors Growing and overwintering plants like tomatoes

Overwintering with survival

Winterising plants can be a difficult and complex process, but it's by no means impossible! Overwintering with survival is the most basic of the overwintering types. The purpose of this type of overwintering is to make sure the plant survives the winter, but it's not meant for further growth. It is a way of activating the plant's natural overwintering function, but with milder conditions than the Danish winter.

Overwintering plants with only survival as a goal requires relatively minimal conditions. The plants should preferably be kept cold, but not too cold, around a temperature that corresponds to the winter temperature where the plants originate. A reasonable temperature is around 14-15 degrees, for example. However, it can often be colder than this without it being a problem. It's the fluctuations in temperature that are really dangerous when it comes to exotic plants. If the temperature is stable and does not fluctuate, many plants can survive at 5-10 degrees centigrade.

It's also important that the plants don't get too much water or light. But the tricky part is that they shouldn't get too little either. The plant's dormancy works best at low humidity, so if you water too much and the humidity rises, it can have very negative consequences. On the other hand, if there is no water in the plant at all, you risk it drying out and dying.

Overwintering with survival can take place in a variety of locations, as long as the temperature is neither too high nor too low. This can be in a cool conservatory, a basement, a garage or a semi-heated greenhouse. 

Want to know more about overwintering plants such as larger trees, for example olive trees or lemon trees, you can read our articles on one of the two topics. 


Overwintering with growth

Overwintering plants where you want the plant to not just hibernate and survive, but to grow instead, is in many ways demanding and takes more time and resources than mere survival. When you want your outdoor plant to continue to grow when it's brought inside for winterisation, you need to try to mimic and maintain the normal conditions that the plant is used to.

The vast majority of common outdoor plants and vegetables, such as tomato plants, have a very high light requirement during growth. It is therefore important to give them plenty of light, which is best done with a grow light lamp, also known as a plant light. A plant light emits light of the wavelengths that plants need to thrive. You can read more about them at our blog.

We humans primarily use sunlight to see, but for plants it is their primary source of energy. Because of this, we often underestimate how much light they actually need. Plants, especially the exotic kind, have really high lighting requirements.

LED grow lights on plant

Tomatoes are one of the Danes' favourite home-grown vegetables, so it's no surprise that it's one of the plants many people would like to try overwintering or growing indoors. However, many people still give their tomatoes far too little light, making them long and lanky.

South America, where tomatoes originate from, is warmer and brighter than in the UK. Because of this, tomatoes are actually a perennial plant in their country of origin. But this is also why we need to give them plenty of light if they are to grow indoors. 

However, non-fruiting plants, such as basil, do not have as high light requirements as fruiting plants. A basil plant can therefore thrive and grow quite normally and undisturbed with a light level of less than one sixth of the light level PPFD(light) of what a tomato plant needs.

Overwintering with growth and fruiting

Balkoni Red F1 Tomato seed 2

Overwintering plants for both growth and fruiting requires even more than the other methods, both in terms of time and equipment. Plants need plenty of light, nutrients, warmth and water in the right conditions if you want them to grow and start fruiting. An easy way to keep an eye on and get a quick and insightful overview of your plant's conditions is with a bluetooth plant sensor. The sensor can measure everything from light intensity and humidity to the nutrient composition of the soil. Overwintering plants becomes much more manageable with a measuring tool.

When a plant is growing indoors during the winter months, it's important that it gets plenty of heat. It doesn't necessarily make economic sense to raise the temperature of your entire house for the sake of a single plant, so it makes sense to heat the plant directly, which can be done with a heating mat. Having a heating mat is really smart as it primarily heats the plant soil and not the leaves and the rest of the plant's upper part. This is beneficial as the root system is the part of the plant that requires the most heat.

When overwintering plants with growth and fruiting, heat and light are very important. The light requirement here is even greater than in the previous type of overwintering, so even more powerful lighting is needed. The best type of lighting for this situation is our powerful quantum boards.

When you start overwintering plants for the purpose of growth and fruiting, you may consider whether you should start growing your plants indoors permanently. Indoor growing can be very effective, especially if you grow your plants hydroponic.

Winterising plants with smart garden

If you think that overwintering plants sounds like a bit of a hassle and you don't really want to lug your herbs in and out, consider starting to grow herbs in a smart garden. A smart garden is an automatic indoor kitchen garden that can be left indoors to grow fresh herbs and other goodies for you all year round. Does the idea of not having to overwinter plants sound exciting to you? read more here.