Tender species and hardiness zone

Technical articles - Climate resilience, Soil erosion, Reduction of IFT

Frost Hardy species Permanent cover

Alfalfa (Medicago sativa) used in permanent cover (wintering species)

A frost-sensitive species does not withstand negative temperatures and disappears with frost, this agronomic characteristic can be useful to facilitate the destruction of a cover and avoid the use of herbicides. Hardiness, on the other hand, allows maintaining soil cover throughout the winter.

Frost sensitivity of different cover crop species, Arvalis & Terres Inovia

Definition

A frost-sensitive species is an organism that is sensitive to frost and deteriorates under its effect. In other words, a frost-sensitive species does not withstand negative temperatures and disappears with frost. Stagnant water, under the effect of frost, increases in volume but also in structural resistance in the form of ice. This volume increase in an organ (plant roots have cells filled with water) literally causes it to crack.

Interest in planting a frost-sensitive species in cover cropping

See the technical sheet on establishing frost-sensitive species in cover cropping

Hardy species

A hardy plant is able to resist cold and frost. More precisely, it can withstand negative temperatures, generally below -3 °C. Some plants are even called "very hardy" because they can tolerate much lower temperatures, down to -20 °C.

Hardiness zones

The concept of hardiness zones is American, leading to the creation of a map of USDA (United States Department of Agriculture) plant hardiness zones, ranging from zone 1 (coldest) to zone 13 (warmest), with 26 "half-zones". France is concerned only by 10 of the 26 USDA half-zones, from zone 6 to zone 10 (no climatic extremes). In Celsius, the major zones are classified over a temperature range of about 5.5 degrees. The hardiness zones on the map are based on the average annual extreme minimum temperature over a 30-year period in the past (from 1991 to 2010), and not on the lowest temperature ever recorded in the past or likely to occur in the future.

Map of USDA zones in France based on meteorological data from 1991 to 2010 (created in 2012)

It is of course important to keep in mind the effects of climate change on the minima and maxima observed today; since 2012, these zones are surely different.

Interest in establishing a hardy species

Hardy species allow for a permanent cover in regions that experience harsh winters. This cover will prevent bare soil in winter, help structure the soil during winter, and fix nitrogen if rustic legumes are established (fodder pea, crimson clover).

Dormancy rating

This index or rating represents the ability to enter more or less prolonged vegetative rest during winter. It is expressed by a rating from 1 (very dormant) to 12 (non-dormant). A low rating corresponds to high dormancy: early vegetative rest in autumn and late restart in spring. The higher the rating, the faster the plant will resume growth in spring and the greater the risk of competition with the following main crop. It is preferable to favor varieties with ratings between 2 and 3 to limit competition risks.