Preparing Your Orchard for Winter

By: Jacob Emling, North Central Research Station Horticulture Specialist

As most orchardists will agree, fall is the time to start thinking about the harvest for next season. Once the fruit is off of the trees, it is time to think about preparing the orchard for the upcoming winter months. During the fall / early winter, the trees are starting to transport the carbohydrates and sugars that have been created in various tissues (such as the leaves) back to storage tissues (roots, woody tissue, and buds). Because of this physiological event, nutrients are able to reach specific tissues, which will help with the survival of the orchard during the winter and help with flowering and early leaf development in the spring.

At this time of year a fall application of fertilizer can be beneficial for many reasons. Proper nutrients at this time allow the plants to “recover” from the fruit load that was removed from the tree. At the time of post-harvest, it is recommended to apply 40% of the seasonal total of the tree’s requirement for nitrogen. Nitrogen in trees (and plants in general) is essential for plants to produce proteins, amino acids, vitamins, and other compounds that are essential for plant growth and development. Common symptoms of nitrogen deficiency in fruit and nut trees include earlier than normal fruit ripening, decreased fruit set, poor development in fruit buds and early leaf abscission (leaves falling off earlier than expected because of the death of the petiole).

Another nutrient that should be applied at a rate of 30% of the tree’s seasonal total is potassium. Potassium is used by the plant to perform various tasks for enzymes, for cell expansion, and for water relations in the plant (referred to as osmoregulation). Most fruit have high concentrations of potassium. An insufficient amount of potassium in the fall can therefore deplete the amount of potassium that is stored in the plant. The nutrient will not be available to the new tissue in the spring until the roots start taking potassium up from the soil solution.

Of all micronutrients, three in particular should be applied to the orchard in the fall / early winter. These micronutrients are zinc, boron, and magnesium. The application of these micronutrients, in addition to nitrogen and potassium, is needed by the plant to start the process of acclimation, which is the ability to withstand cold temperatures and different physiological processes that occur in the fall – important in many parts of the country. Zinc is important for protein production in the plant. When zinc deficiency is apparent, the plant appears smaller in stature compared to a healthy plant. In contrast to zinc, magnesium in plants has been documented to be important for proper development of fruit. This micronutrient is highly mobile, which allows the fruit to draw on the magnesium that is found in the leaves around the fruit. When magnesium levels are not up to the recommended rates, plants will start early leaf shedding. This early shedding of leaves can have negative effects on the amount of nutrients that have been transported to the storage tissues. Boron is also a very important micronutrient for many processes that occur throughout the tree during both the fall and the spring. In particular, boron is needed for the proper fertilization of flower buds in the spring time. It has also been documented that applications of boron in the fall help to improve the amount of boron that is available for the flower buds, which will enhance fruit quality in the following growing season. It has been recommended to make the majority of micronutrient applications in the fall due to the fact that in the spring the plant then relies on what has been stored in the roots and various storage tissues.

Winter-trees

Of course all fertilizer recommendations should be based on soil tests, information about particular climate, and local recommendations from a fertilizer professional. During this time of year a soil application can be helpful, but if the plants still have a healthy canopy, a foliar application would be the most efficient way of getting the proper nutrients to the tissues that require them. Just remember that proper nutrition in the orchard is a year-round matter and should be considered to allow for the best possible yield and quality of the orchard.

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