{"id":13295,"date":"2026-05-19T03:14:40","date_gmt":"2026-05-19T03:14:40","guid":{"rendered":"https:\/\/portalciruelas.com\/2026\/05\/19\/congreso-ipa-2026-modena-2\/"},"modified":"2026-05-19T03:21:49","modified_gmt":"2026-05-19T03:21:49","slug":"potassium-optimization-plum-trees","status":"publish","type":"post","link":"https:\/\/portalciruelas.com\/en\/2026\/05\/19\/potassium-optimization-plum-trees\/","title":{"rendered":"Optimizing Potassium Programs in Plum Trees: The Key Lies in the Timing and Harvest Load (Northern Hemisphere)"},"content":{"rendered":"

Potassium (K) plays a crucial role in plum production: it directly impacts fruit size, sugar accumulation, and yield after drying. Although many growers use foliar potassium to supplement their soil fertilization programs, the results can often be inconsistent.<\/p>\n

Recent field trials, which used rubidium (Rb) as a tracer to understand nutrient movement, reveal the reason for this variability. The results demonstrate that the moment of application<\/strong> and the harvest load<\/strong> These are the factors that determine whether foliar potassium actually reaches the fruit or is wasted.<\/p>\n

Below, we break down the latest findings and offer practical recommendations based on research by Dr. Rich Rosecrance and Karla Caldera (California State University, Chico) published in Sac Valley Orchards<\/em>.<\/p>\n

Soil first: The foundation of your fertilization program<\/h2>\n

Before looking at the leaves, it's vital to ensure the soil is healthy. Applying potassium to the soil remains the most important strategy.<\/p>\n

Studies showed that all potassium sources applied to the soil (coarse SOP, fine SOP, and KTS) had similar performance:<\/p>\n

    \n
  • Potassium in the leaves remained within an adequate range.<\/li>\n
  • There were no significant differences in fruit size.<\/li>\n
  • Although the KTS applied later showed slightly lower levels, it remained within the sufficiency range.<\/li>\n<\/ul>\n

    Practical conclusion:<\/strong> Keep soil potassium as the unshakeable foundation of your program. Choose products based on price and ease of application, not on expected performance differences.<\/p>\n

    Foliar Potassium: The timing of application is everything<\/h2>\n

    If you decide to apply foliar potassium, the application schedule is your best ally.<\/p>\n

    Research shows that foliar potassium moves out of the leaf within 3 to 5 weeks after application:<\/p>\n

      \n
    • May \u2013 early June:<\/strong> Excellent movement of potassium towards the fruit is observed.<\/li>\n
    • July onwards:<\/strong> Much of the potassium remains trapped in the leaves.<\/li>\n<\/ul>\n

      At the beginning of the season, the tree transports nutrients very efficiently to the developing fruit. However, later in the season, this movement slows down dramatically, causing foliar potassium to rarely reach its final destination.<\/p>\n

      Practical conclusion:<\/strong> If you're going to invest in foliar potassium sprays, do it early (between May and early June). Avoid relying on late applications to try to improve fruit size.<\/p>\n

      The harvest load: The true engine of absorption<\/h2>\n

      The factor that most impacts whether foliar potassium reaches the fruit is the crop load of the tree.<\/p>\n

        \n
      • In years of abundant harvests (heavy load):<\/strong> The fruits act as a strong "sink", aggressively extracting potassium from the leaves into themselves.<\/li>\n
      • In years of light harvests (low yield):<\/strong> That demand simply doesn't exist. Most of the foliar potassium remains in the leaves or is stored in the branches.<\/li>\n<\/ul>\n

        Practical conclusion:<\/strong> Foliar potassium offers a high return on investment (ROI) in years of heavy harvests. However, in years of low production, its profitability is significantly lower.<\/p>\n

        Choosing a foliar fertilizer: Efficiency vs. Cost<\/h2>\n

        Not all foliar fertilizers are the same when it comes to moving nutrients to the fruit.<\/p>\n

        Potassium nitrate (KNO\u2083) was more effective at moving potassium into the fruit than potassium sulfate (K\u2082SO\u2084). In fact, sulfate sources were only between 65% and 70% as effective. Since KNO\u2083 is typically only slightly more expensive, you're often paying a little more for a material that delivers significantly more potassium to the fruit.<\/p>\n

          \n
        • With heavy load:<\/strong> The greater efficiency of KNO\u2083 justifies the investment.<\/li>\n
        • With a light load:<\/strong> A cheaper source like K\u2082SO\u2084 makes more strategic sense.<\/li>\n<\/ul>\n

          6 Practical recommendations for your garden<\/h2>\n
            \n
          1. Maintain a solid potassium program in the soil.<\/strong> It is the cornerstone of your garden's nutrition.<\/li>\n
          2. Use foliar potassium as a supplement<\/strong>, never as a replacement for soil fertilizer.<\/li>\n
          3. Spray early<\/strong> (between May and early June) to ensure that the nutrient reaches the fruit.<\/li>\n
          4. Focus on the blocks with the highest harvest load.<\/strong> That's where you'll see the real return on investment.<\/li>\n
          5. Consider using KNO\u2083<\/strong> when the demand for the crop is high (heavy harvests).<\/li>\n
          6. Avoid relying on late-season foliar sprays<\/strong> hoping to improve the size or drying of the fruit.<\/li>\n<\/ol>\n
            \n

            Source: Adapted from the article "Optimizing Potassium Programs in Prune Orchards: Timing and Crop Load" by Dr. Rich Rosecrance and Karla Caldera (California State University, Chico), published in Sac Valley Orchards.<\/em><\/p>","protected":false},"excerpt":{"rendered":"

            El potasio (K) desempe\u00f1a un papel fundamental en la producci\u00f3n de ciruelas: impacta directamente en el tama\u00f1o del fruto, la acumulaci\u00f3n de az\u00facares y el rendimiento tras el secado. Aunque muchos productores recurren al potasio foliar para complementar sus programas de fertilizaci\u00f3n del suelo, los resultados a menudo pueden ser inconsistentes. Recientes ensayos de campo, […]<\/p>\n","protected":false},"author":1,"featured_media":13294,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"pagelayer_contact_templates":[],"_pagelayer_content":"","rank_math_title":"","rank_math_description":"","rank_math_focus_keyword":"","footnotes":""},"categories":[76],"tags":[],"class_list":["post-13295","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-saber-agro"],"_links":{"self":[{"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/posts\/13295","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/comments?post=13295"}],"version-history":[{"count":2,"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/posts\/13295\/revisions"}],"predecessor-version":[{"id":13298,"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/posts\/13295\/revisions\/13298"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/media\/13294"}],"wp:attachment":[{"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/media?parent=13295"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/categories?post=13295"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/portalciruelas.com\/en\/wp-json\/wp\/v2\/tags?post=13295"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}