What do plants do in winter?

In the white season it can get quite cold in our latitudes. How do plants survive in winter and do they photosynthesize even in the cold months?

Animals grow a thick coat in winter, feed on an insulating layer of fat in summer and autumn, fall into hibernation or hibernate. We humans put on warm clothes, drink tea or try to keep warm in other ways. After all, we are warm creatures that need a specific temperature to survive. Plants, on the other hand, are cold-blooded organisms. They have developed ingenious strategies to survive the cold winter.

Overwintering strategies of plants

The overwintering strategies of plants can be classified into different methods. In general, it is always about creating an energy store and protecting the meristem - i.e. the formation tissue of the buds, which serves as the starting point for budding in spring. There are 4 strategies:

Overwintering plants as seeds

Seed plants, whose bodies are scheduled to die off in winter, overwinter thanks only to their seeds. It contains both storage substances and the embryonic stem tissue, i.e. the meristem, with the help of which new life is possible.

Hibernation of perennials: retreat to storage organs

Perennials are perennial, herbaceous plants that survive for several years and thus also the winter. They shift energy-rich storage substances into the roots, alternatively into bulbs, tubers or rhizomes. The meristematic tissue is found very close to the soil surface in the form of buds or inconspicuous dormant eyes.

Hibernation of deciduous trees and shrubs: retreat into the wood

The fact that deciduous trees do not store energy in the leaves but in the wood is clearly recognizable from the autumn colour. The foliage turns yellow because energy-rich substances are recycled and transported into the woody part via the petiole. The buds for re-sprout are shielded under bud scales on trees, but often several meters above the ground and must be protected from the tree by further frost protection measures.

Overwintering of evergreen plants: frost protection of leaf and bud

Evergreen plants do not shed their leaves. They therefore also transfer fewer reserve substances into the wood body, instead they have to adapt their leaves to the cold weather through their structure and the storage of various substances. The buds overwinter in a state of dormancy, which is brought about by a special cocktail of hormones.

Do plants photosynthesize in winter?

Not all plants photosynthesize in winter, but evergreens do, albeit to a lesser extent.

To answer the question in more detail, it makes sense to take a quick look at photosynthesis itself. Photosynthesis describes the process of producing organic material, i.e. building blocks for the plant body, with the help of light energy and inorganic compounds. The main role in this process is played by green chlorophyll. Plants that shed their green parts or let them die off in winter can therefore not carry out photosynthesis until the green plant parts are available again.
Evergreen plants, on the other hand, are able to gain energy from sunlight all year round. However, the sunlight in our latitudes is weaker in winter and only available for a shorter time. Coupled with cold, which inhibits photosynthesis, this results in only a very low photosynthesis performance. Therefore, even evergreen plants do not continue to grow in winter, but can only cover their daily energy requirements to maintain frost hardiness.

That's what plants do before winter

Preparations for the cold season begin early. Because overnight, no plant is prepared for sub-zero temperatures and diet. The cold and shorter days adjust their hormone balance in such a way that the plants gradually go into hibernation. What sounds like a break is initially associated with a lot more work than you can see from the outside. These processes take time and should not be disturbed: by pruning, too much water or fertilization with the wrong nutrients we can hamper the preparations of the plants, jeopardizing winter hardiness is.

Here are the steps plants need to take before winter:

Storage of reserve materials

As described above, plants store their energy reserves in different places. Plants have a lot of work to do in autumn to transfer them to the appropriate plant organs.

retreat into the wood

Leaf discolouration can be observed in autumn on most of our local deciduous trees. This phenomenon occurs because the chlorophyll - which makes the leaves appear green - is recycled and carried away. Other high-energy material is also transferred from the leaves to the trunk.

Below the bark, water-rich cell organelles, the vacuoles, divide. A few large vacuoles give rise to numerous small ones. Above all, sugar accumulates in them, but also proteins and other dissolved substances. Essential elements such as potassium, magnesium and phosphorus are also removed from the leaves before they are dropped.
Starch is stored in the amyloplast as an energy reserve. In the course of the year, the trees draw on these reserves, so that they are largely used up again in May when the leaves unfold.
After all the important nutrients and minerals have been stored, the foliage is shed. This keeps the area for snow loads and crown movements, which can lead to fractures, to a minimum.
Trees may appear inactive on the outside in winter, but they are constantly engaged in cellular respiration. They thus provide energy for the operation of vital metabolic processes.

Withdrawal into the soil: tubers, bulbs, rhizomes and roots

Lots of herbaceous plants like that lily of the valley (Convallaria majalis), the common goutweed (Aegopodium podagraria) or ginger (Zingiber officinale) form so-called rhizomes. It is a shoot system that grows below or just above the ground and has the task of storing reserve substances. Thanks to these stored substances, including starch in particular, many plants can overwinter in the soil. Onion plants use transformed leaves as storage organs. Below the surface of the earth, these storage organs are largely protected from frost.

Plants that hibernate underground appreciate our help! Mulch can be applied to reinforce an insulating protective layer. Our Plantura organic pine bark not only protects against drying out, but also suppresses weed growth.

Withdrawal to the seed: propagation and winter protection in one

Plants can also overwinter as seeds. These usually consist of the seed coat, a nutritive tissue and the embryo, which can be at different stages of development. Depending on the type of seed, the nutritive tissue is of a different nature. Seeds of legumes such as beans (vicia), Peas (Pisum) and lenses (Lens) are high in protein. The seeds of grains such as wheat (triticum) or oats (avena) and deciduous trees such as oak (Quercus) and sweet chestnut (Castanea) store energy primarily in the form of starch. Some seeds, like the hazelnut (corylus) and the walnut (juglans), form seeds with fat as a storage body. No wonder we humans use many of these seeds for food. In seeds, too, the nutritive tissue is not only used for the step into life, i.e. germination, but also for greatly reduced cell respiration. So each seed is a living, breathing embryo. Due to a very low water content, the hard seed coat and the high concentration of osmotically active substances, it is well protected from freezing.

Autumn color of the leaves

Even independently of the fact that the yellow autumn color develops as a result of the relocation of chlorophyll from the leaves to protected parts of the plant, leaves are coloured. You can see that from the fact that some evergreen trees, for example mahonia (mahonia), turning their foliage brightly colored in autumn. Responsible are anthocyanins and carotenoids, which are formed to protect against frost and too much sunlight. Because evergreen plants have a problem in winter: If it is very cold at the same time, but the sun is shining, a lot of high-energy radiation hits the leaf. However, cold slows down all processes in the plant cell, so that the solar energy cannot be stored in a usable form. A harmful excess of energy is created that can damage cell components - similar to when we get sunburn. The anthocyanins, which appear red or violet to us, act as protection against these harmful effects.
A precise explanation of the leaf coloring in autumn can be found in our special article.

Plants produce their own antifreeze

Why don't plants just freeze in winter, like vegetables in the freezer? Why can the lawn be walked on even in frost without the blades breaking like ice needles? Freezing the cell would be fatal because the water expands and would simply burst the cells.
The answer can be explained using the example of the sea. If water is enriched with a sufficiently high concentration of osmotically active substances, its freezing point is reduced. In the sea, this osmotically active substance is salt. In plant cells, various sugars, alcohol compounds and, crucially, potassium act as antifreeze agents.

Tip: This is also the reason for autumn fertilization like this autumn lawn fertilization. Special fertilizers like ours Plantura Organic Autumn Lawn Fertilizer promote the winter hardiness of the lawn instead of endangering it. They do this by introducing potassium, which is stored in the vacuoles as an antifreeze.

In the leaves of common ivy (Hedera helix) the freezing point can be reduced to -3 °C by storing sugar, for example. Other molecules that prevent the formation of ice crystals in the cells also contribute to this.
Thanks to these special precautions in the storage organs, plants can endure temperatures below -45 °C. Of course, this does not apply to every type of plant, but depends on which area it comes from and what anti-freeze precautions are built into its genetics.

tip: The 10 best evergreen plants we present to you in an extra article.

Protected buds: starting point for new life

Leaf and flower buds are often established in the previous year and then enter a dormant phase to await winter. The signal for this is given by low temperatures and a short day length. Processes are now initiated via hormones in order to protect the leaf and flower buds. For this purpose they are surrounded by bud scales. Inside these scales, a white fur of dead hair forms, which has an insulating effect. Of course, “antifreeze” is also stored. In this state, the buds defy cold and frost. Only when the days get longer and warmer again does the frost hardness decrease, the water content increases and the tissue develops further. At this stage, the buds are at high risk of being damaged by late frosts.

It's warmest on the ground: geophytes like that spring bloomers hide their buds in the ground. Hemicryptophytes, which include most perennials, at least hide their buds under insulating foliage. Plants that have their renewal tissue at a height of up to 30 cm are called chamaephytes. Their buds are protected by the snow cover. If the buds are even higher, one speaks of phanerophytes, which include all woody plants. The higher, i.e. more exposed to the wind, the buds are, the more effectively they must be protected from frost.

Tip: In the spring, fertilization and watering as well as placing in a warm place can be used to prematurely sprout plants. This is the ideal time for repotting pot and house plants and adding fertilizer for a successful start to the new growing season! Our Plantura organic indoor and green plant fertilizer is ideal for most indoor plants thanks to its NK ratio of 3-4. But caution is advised: With this treatment we are provoking a reduction in winter hardiness, so the driven plants should be protected from frost.

As you can see, there are ingenious tactics how trees overwinter and other plants survive the winter. But by no means all of them are well protected against the icy temperatures. So we're giving you tips on how to make yours Overwinter plants properly.