La nature a besoin du froid

Mais n’ayez pas peur du froid : il fait fleurir vos plantes !

Pendant l’hiver de nombreuses plantes et leurs différents organes entrent en dormance. Cette dormance se traduit par l’inactivité des cellules et du métabolisme. Mais plusieurs phénomènes importants se produisent alors et le froid va stimuler la synthèse d’hormones qui vont permettre la croissance ultérieure des bourgeons.
Pour lever cette dormance, il faut un certain nombre d’heures de froid (avec une température plus ou moins froide selon les espèces).
La vernalisation, c’est le nom que l’on donne à ce besoin de froid qu’ont certaines plantes pour pouvoir croitre, fleurir.
En botanique, la vernalisation se réfère à une période de froid subie par la plante ou la graine et nécessaire pour la faire passer du stade de repos au stade actif, d’un stade végétatif à un stade reproductif qui l’amènera à fleurir.
 Comme beaucoup d’arbres fruitiers, le pommier a besoin de plus d’un millier d’heures de froid à moins de 7°C environ. Certaines espèces sont donc limitées géographiquement par ce besoin de froid et se développent dans des pays froids. Bien sûr, toutes les espèces n’ont pas ce niveau de besoin et par exemple le pêcher n’a besoin que de courtes périodes de froid et certaines variétés pas du tout.

La non satisfaction des besoins en froid d’un arbre fruitier peut être caractérisée par les symptômes suivants :
– Une chute des bourgeons floraux et végétatifs                                             
– Une feuillaison faible avec un manque de vigueur des rameaux
 – Une floraison tardive                                            
– Des fleurs déformées ayant peu de pollen                                              
– Un calibre et une maturité des fruits très hétérogène                                              
– Un rendement et une qualité des fruits médiocres

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