Winter Hardiness of Winter Crops: Factors Affecting Overwintering and How to Prepare Crops in Autumn

The winter hardiness of winter crops is determined by five main factors: the genetic characteristics of the crop and variety, plant condition in autumn, the process of cold acclimation, nutrient availability, and wintering conditions. To reduce the risk of winter damage, it is essential to ensure timely emergence, root development, and balanced nutrition without excessive stimulation of plant growth.

Autumn preparation is important for winter wheat, barley, rye, triticale, and winter rapeseed. However, these crops should be assessed differently: in cereals, particular attention is paid to the tillering node, while in rapeseed, the focus is on the root collar, growing point, and rosette development.

What Is the Difference Between Winter Hardiness and Frost Resistance?

Frost resistance is the ability of a plant to withstand low temperatures while maintaining viability. Winter hardiness is the ability to survive a combination of unfavourable winter conditions, including frost, thaws, ice crust, waterlogging, snow mould, and winter desiccation.

A frost-resistant variety may still suffer from prolonged waterlogging or ice crust. Therefore, choosing a variety with high frost resistance is an important part of crop management, but it does not guarantee successful overwintering.

How Does Cold Acclimation Occur in Winter Crops?

Cold acclimation in winter crops is a gradual physiological adaptation to low temperatures during which plants reorganise their metabolism and increase their frost resistance. This process is influenced by temperature, light, water availability, genetic characteristics, and the growth stage.

The following changes occur during cold acclimation:

• Accumulation of soluble sugars and other protective compounds. They participate in regulating water balance and protecting cellular structures. Stored carbohydrates provide energy for maintaining vital functions and resuming growth.
• Changes in cell membranes. Changes in their properties help cells withstand cold and dehydration associated with ice formation outside the cells.
• Changes in metabolism. Growth slows down, while cold-response mechanisms and the synthesis of protective proteins are activated.

Gradual cooling under sufficient light conditions generally promotes cold acclimation. A prolonged warm autumn may support active growth, but a large green biomass does not necessarily mean that plants are ready for frost.

Cold acclimation and vernalisation are different processes. Cold acclimation increases resistance to low temperatures. Vernalisation provides the required period of low temperatures for winter crops to subsequently transition to reproductive development.

What Should the Condition of Winter Crops Be Before Winter to Ensure Successful Overwintering?

Plants should enter winter sufficiently developed, well-rooted, and cold-acclimated. At the same time, excessive autumn growth is not an advantage.

There is no universal number of leaves or shoots that applies to all winter crops. The appropriate benchmarks depend on the specific crop, variety or hybrid, and growing region.

How Do Sowing Dates Affect Winter Hardiness?

Optimal sowing dates allow plants to develop the necessary organs and undergo cold acclimation before the onset of sustained cold weather. It is important to assess not only the sowing date but also the date of emergence and the actual course of autumn vegetation.

When emergence occurs late, plants may not have enough time to develop their root systems, while cereals may not have sufficient time to tiller. Sowing too early during a warm autumn may result in excessive growth and overdevelopment of above-ground biomass.

Two fields sown at the same time may have different levels of winter readiness due to differences in soil moisture, emergence rates, nutrition, and plant condition.

Which Nutrients Are Important for the Winter Hardiness of Winter Crops?

Preparing winter crops for winter requires a balanced supply of nitrogen, phosphorus, potassium, sulphur, and other essential nutrients. The effect of additional fertilisation depends on whether a nutrient deficiency exists and whether plants are able to absorb the nutrient.

No single nutrient or product can guarantee successful overwintering. Additional fertiliser application when nutrient availability is already sufficient does not necessarily improve winter hardiness.

The fertilisation programme should be developed based on soil analysis, the preceding crop, fertilisers already applied, moisture availability, and crop condition.

Why Does Air Temperature Not Show the Full Risk of Winterkill?

For the overwintering of winter crops, the temperature at the depth of the tillering node or the developed root collar and growing point is particularly important. It may differ from air temperature depending on snow cover and field surface conditions.

Snow reduces soil cooling. Therefore, the same frost on an exposed field and under snow cover can have different consequences.

When assessing the risk, consider:

• temperature at the level of vital plant organs;
• duration of frost;
• presence and distribution of snow;
• degree of cold acclimation;
• plant condition before the onset of cold weather.

It is incorrect to specify a single “critical temperature” for all winter crops without taking these factors into account.

Why Are Thaws and Ice Crust Dangerous?

During prolonged thaws, winter crops may partially lose the frost resistance they have acquired. Subsequent sudden drops in temperature increase the risk of damage.

Ice crust and waterlogging create other threats: they can restrict gas exchange and worsen conditions for plant survival. The level of risk depends on the duration of exposure, temperature, and the characteristics of the specific field area.

After thaws, particular attention should be paid to low-lying areas, places where meltwater accumulates, and fields covered with continuous ice crust.

How to Assess the Readiness of Winter Crops for Winter?

Before the end of autumn vegetation, inspect the field and record the results.

• Check crop density and uniformity. Identify thin, overly dense, and unevenly developed areas.
• Determine the growth stage. In cereals, assess tillering; in rapeseed, assess the rosette, root collar, and position of the growing point.
• Inspect the roots. Check root establishment, damage, and signs of suppressed growth.
• Assess plant nutrition. Compare soil analysis results with previous fertiliser applications. Changes in leaf colour are a reason for further diagnosis, not sufficient grounds for choosing a fertiliser.
• Identify high-risk areas. Pay attention to waterlogging, soil compaction, and uneven plant development.
• Record crop condition. Photographs and notes from individual field zones will help assess the effects of overwintering in spring.

If the crop stand is weak, first identify the cause. Additional nutrition does not automatically eliminate the consequences of late emergence, insufficient moisture, or root damage.

Frequently Asked Questions

Can Winter Hardiness Be Improved Through Fertilisation?

Correcting nutrient deficiencies helps plants develop normally and prepare for cold conditions. However, fertilisers cannot replace cold acclimation, proper variety selection, or timely sowing.

Is It Necessary to Apply More Potassium for Better Overwintering?

Potassium is important for water balance, metabolic processes, and the accumulation of assimilates. However, the need for additional application should be determined by soil nutrient availability and crop requirements. The principle that “more potassium means higher winter hardiness” is not universally applicable.

Does Yellowing of Leaves in Winter Mean That the Crop Has Died?

No. Leaf damage does not always mean that the plant has died. In cereals, the viability of the tillering node is assessed, while in rapeseed, the growing point is examined. The plants’ ability to resume growth is also important.

Can Well-Developed Crops Still Overwinter Poorly?

Yes. Even well-developed plants can suffer from insufficient cold acclimation, prolonged thaws, ice crust, waterlogging, or severe frost without protective snow cover.

How Does Makosh Help Plan Nutrition for Winter Crops?

To discuss a fertilisation programme with an agronomist, prepare information about the crop, variety or hybrid, emergence date, preceding crop, fertilisers applied, and crop condition.

Contact Makosh specialists through the Agronomist 24/7 programme. If you do not have up-to-date information about soil nutrient availability, start with the Soil Audit service.