{"id":5218,"date":"2026-10-12T20:50:09","date_gmt":"2026-10-12T20:50:09","guid":{"rendered":"https:\/\/www.tomat-pomidor.com\/en\/?p=5218"},"modified":"2026-10-12T20:50:09","modified_gmt":"2026-10-12T20:50:09","slug":"can-potassium-feeding-trigger-tomato-leaf-mold","status":"publish","type":"post","link":"https:\/\/www.tomat-pomidor.com\/en\/can-potassium-feeding-trigger-tomato-leaf-mold\/","title":{"rendered":"Can Potassium Feeding Trigger Tomato Leaf Mold?"},"content":{"rendered":"\n\n<div class=\"kk-star-ratings kksr-auto kksr-align-left kksr-valign-top\"\n    data-payload='{&quot;align&quot;:&quot;left&quot;,&quot;id&quot;:&quot;5218&quot;,&quot;slug&quot;:&quot;default&quot;,&quot;valign&quot;:&quot;top&quot;,&quot;ignore&quot;:&quot;&quot;,&quot;reference&quot;:&quot;auto&quot;,&quot;class&quot;:&quot;&quot;,&quot;count&quot;:&quot;0&quot;,&quot;legendonly&quot;:&quot;&quot;,&quot;readonly&quot;:&quot;&quot;,&quot;score&quot;:&quot;0&quot;,&quot;starsonly&quot;:&quot;&quot;,&quot;best&quot;:&quot;5&quot;,&quot;gap&quot;:&quot;5&quot;,&quot;greet&quot;:&quot;Share your rating&quot;,&quot;legend&quot;:&quot;0\\\/5 - (0 votes)&quot;,&quot;size&quot;:&quot;24&quot;,&quot;title&quot;:&quot;Can Potassium Feeding Trigger Tomato Leaf Mold?&quot;,&quot;width&quot;:&quot;0&quot;,&quot;_legend&quot;:&quot;{score}\\\/{best} - ({count} {votes})&quot;,&quot;font_factor&quot;:&quot;1.25&quot;}'>\n            \n<div class=\"kksr-stars\">\n    \n<div class=\"kksr-stars-inactive\">\n            <div class=\"kksr-star\" data-star=\"1\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" data-star=\"2\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" data-star=\"3\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" data-star=\"4\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" data-star=\"5\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n    <\/div>\n    \n<div class=\"kksr-stars-active\" style=\"width: 0px;\">\n            <div class=\"kksr-star\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n            <div class=\"kksr-star\" style=\"padding-right: 5px\">\n            \n\n<div class=\"kksr-icon\" style=\"width: 24px; height: 24px;\"><\/div>\n        <\/div>\n    <\/div>\n<\/div>\n                \n\n<div class=\"kksr-legend\" style=\"font-size: 19.2px;\">\n            <span class=\"kksr-muted\">Share your rating<\/span>\n    <\/div>\n    <\/div>\n<div class=\"tldr-box\" style=\"background: #f4f9f4; padding: 20px; border-left: 5px solid #4CAF50; margin-bottom: 30px; border-radius: 4px;\">\n<h3>\ud83d\udccc Quick Summary: The Great Calcium vs. Potassium Mix-Up<\/h3>\n<ul>\n<li>\ud83c\udf45 <strong>The BER Mistake:<\/strong> Blossom End Rot (BER) is caused by a lack of <em>Calcium<\/em>, not Potassium. Many growers confuse the two! Feeding a plant suffering from BER with Potassium will actually make the rot much worse.<\/li>\n<li>\ud83d\uded1 <strong>Nutrient Lockout:<\/strong> Potassium and Calcium are antagonistic elements in the soil. If you dump too much Potassium into your beds, the plant roots literally cannot absorb Calcium, even if it is present in the soil.<\/li>\n<li>\ud83c\udf42 <strong>Does Potassium Cause Leaf Mold?<\/strong> A weakened plant is a magnet for diseases. While Potassium doesn&#8217;t directly create Tomato Leaf Mold (Cladosporium), triggering a severe Calcium deficiency by overfeeding Potassium severely weakens the plant&#8217;s immune system.<\/li>\n<li>\ud83e\uddfd <strong>The Power of the Pressure Washer:<\/strong> Eradicating Leaf Mold from a greenhouse takes extreme willpower. Growers share their success using pressure washers, laundry soap, and copper sulfate to scrub the greenhouse walls in the fall.<br \/>\nPhoto author: <a id=\"ips_uid_9600_4\" class=\"ipsType_break\" title=\"\u041f\u0435\u0440\u0435\u0439\u0442\u0438 \u0432 \u043f\u0440\u043e\u0444\u0438\u043b\u044c MrsFlower\" href=\"https:\/\/www.tomat-pomidor.com\/gallery\/image\/91065-%D0%9A%D0%B2%D0%B5%D1%80%D1%85%D1%82%D0%BE%D1%80%D0%BC%D0%B0%D1%88%D0%B5%D1%87%D0%BD%D1%8B%D0%B9%20%D1%81%D0%BF%D0%BE%D1%81%D0%BE%D0%B1%20%D0%B2%D1%8B%D1%80%D0%B0%D1%89%D0%B8%D0%B2%D0%B0%D0%BD%D0%B8%D1%8F%20%D1%82%D0%BE%D0%BC%D0%B0%D1%82%D0%BE%D0%B2\/\" target=\"_blank\" rel=\"noopener\" data-ipshover=\"\" data-ipshover-target=\"https:\/\/www.tomat-pomidor.com\/profile\/57412-mrsflower\/?do=hovercard&amp;referrer=https%253A%252F%252Fwww.tomat-pomidor.com%252Fgallery%252Falbum%252F3371-%2525D0%25259C%2525D0%2525BE%2525D0%2525B9%252520%2525D0%2525BE%2525D0%2525B3%2525D0%2525BE%2525D1%252580%2525D0%2525BE%2525D0%2525B4%252Fpage%252F3%252F\">MrsFlower<\/a><\/li>\n<\/ul>\n<\/div>\n<div class=\"add-review-cta\" style=\"margin: 20px 0; padding: 15px; background: #f9f9f9; border-left: 4px solid #4CAF50; border-radius: 4px;\"><strong>\ud83d\udcac Have you ever confused Potassium and Calcium?<\/strong> <a href=\"#wpdcom\">Tell us how you treat Blossom End Rot below!<\/a><\/div>\n<div class=\"forum-post\">\n<div class=\"author-header\">\n<div class=\"forum-avatar\">V<\/div>\n<div class=\"author-meta\">\n<div class=\"author-name\">Valtwelve (Valery) <span class=\"author-stats\">\u2b50 Pro Grower (1,847 posts)<\/span><\/div>\n<div class=\"author-geo\">\ud83d\udccd Between Samara &amp; Ufa (USDA Zone 4a) | \ud83d\udcc5 September 10, 2021<\/div>\n<\/div>\n<\/div>\n<div class=\"post-content\">\n<blockquote><p><strong>Marat wrote:<\/strong><br \/>\nLast year I fed them with Potassium to treat Blossom End Rot. This year I excluded that feeding. Somewhere on this forum, I read that Potassium plays a role in the development of Cladosporium (Leaf Mold)&#8230;<\/p><\/blockquote>\n<p>Actually, no plant can grow without Potassium, especially a tomato. Potassium makes up more than 50% of the total nutrients inside a tomato fruit! You probably have soil that is already very rich in Potassium if your tomatoes grow well without additional feedings. Do you have loamy soil?<\/p>\n<\/div>\n<\/div>\n<div class=\"forum-post\">\n<div class=\"author-header\">\n<div class=\"forum-avatar\">M<\/div>\n<div class=\"author-meta\">\n<div class=\"author-name\">Marat <span class=\"author-stats\">\u2b50 Expert (3,308 posts)<\/span><\/div>\n<div class=\"author-geo\">\ud83d\udccd Kazan (USDA Zone 4a) | \ud83d\udcc5 September 10, 2021<\/div>\n<\/div>\n<\/div>\n<div class=\"post-content\">Yes, Valery, I have loamy soil. Up until last year, I planted tomatoes the old-fashioned way: I put humus and sifted wood ash directly into the planting holes. During the season, I would feed them a couple of times with diluted chicken manure.But at the peak of the season, a very severe case of Blossom End Rot appeared. Someone advised me to feed them with Potassium (as a root drench), which I did. Shortly after that, a massive outbreak of Cladosporium started! In the fall, I read in someone&#8217;s diary here that Potassium feedings provoke Leaf Mold. I won&#8217;t claim it is an absolute fact, but that is exactly what happened to me.<\/p>\n<\/div>\n<\/div>\n<div class=\"forum-post\">\n<div class=\"author-header\">\n<div class=\"forum-avatar\">A<\/div>\n<div class=\"author-meta\">\n<div class=\"author-name\">Aleksan9ra (Ludmila) <span class=\"author-stats\">\u2b50 Pro Grower (15,056 posts)<\/span><\/div>\n<div class=\"author-geo\">\ud83d\udccd Moscow Region (USDA Zone 4b) | \ud83d\udcc5 September 10, 2021<\/div>\n<\/div>\n<\/div>\n<div class=\"post-content\">Marat, I still think it is a pure coincidence. How could Potassium possibly provoke Leaf Mold, especially from just one feeding?<\/div>\n<\/div>\n<div class=\"forum-post\">\n<div class=\"author-header\">\n<div class=\"forum-avatar\">G<\/div>\n<div class=\"author-meta\">\n<div class=\"author-name\">gala7496 (Galina) <span class=\"author-stats\">\u2b50 Pro Grower (2,474 posts)<\/span><\/div>\n<div class=\"author-geo\">\ud83d\udccd Moscow Region (USDA Zone 4b) | \ud83d\udcc5 September 10, 2021<\/div>\n<\/div>\n<\/div>\n<div class=\"post-content\">\n<blockquote><p><strong>Aleksan9ra wrote:<\/strong><br \/>\nHow could Potassium possibly provoke Leaf Mold&#8230;<\/p><\/blockquote>\n<p>Good morning! Last year I also had a terrible case of Leaf Mold. I decided to remove the entire top layer of soil in the beds and replace it with fresh soil and humus.<\/p>\n<p>I also thoroughly washed the greenhouse. First, I just hosed the dirt off with plain water, then I scrubbed everything with laundry soap, rinsed it again, and finally sprayed the entire inside surface with copper sulfate. I don&#8217;t know if this is what helped, but my tomatoes are still standing healthy in the greenhouse right now! I&#8217;ll probably pick the red ones this weekend and leave the green ones on the vine.<\/p>\n<\/div>\n<\/div>\n<div class=\"forum-post\">\n<div class=\"author-header\">\n<div class=\"forum-avatar\">M<\/div>\n<div class=\"author-meta\">\n<div class=\"author-name\">Marat <span class=\"author-stats\">\u2b50 Expert (3,308 posts)<\/span><\/div>\n<div class=\"author-geo\">\ud83d\udccd Kazan (USDA Zone 4a) | \ud83d\udcc5 September 10, 2021<\/div>\n<\/div>\n<\/div>\n<div class=\"post-content\">\n<blockquote><p><strong>Aleksan9ra wrote:<\/strong><br \/>\nMarat, I still think it is a pure coincidence.<\/p><\/blockquote>\n<p>I am not ruling out a coincidence, but I am not denying it either. We will live and see. But the phrase &#8220;feed with potassium and you get leaf mold&#8221; is stuck in my head from reading it here.<\/p>\n<blockquote><p><strong>gala7496 wrote:<\/strong><br \/>\nI also thoroughly washed the greenhouse. First, I just hosed the dirt off with plain water&#8230;<\/p><\/blockquote>\n<p>By the way, I also washed my greenhouse in the fall using a pressure washer&#8230;<\/p>\n<\/div>\n<\/div>\n<div class=\"forum-post\">\n<div class=\"author-header\">\n<div class=\"forum-avatar\">V<\/div>\n<div class=\"author-meta\">\n<div class=\"author-name\">Valtwelve (Valery) <span class=\"author-stats\">\u2b50 Pro Grower (1,847 posts)<\/span><\/div>\n<div class=\"author-geo\">\ud83d\udccd Between Samara &amp; Ufa (USDA Zone 4a) | \ud83d\udcc5 September 10, 2021<\/div>\n<\/div>\n<\/div>\n<div class=\"post-content\">\n<blockquote><p><strong>Marat wrote:<\/strong><br \/>\n&#8230;a very severe case of Blossom End Rot appeared. Someone advised me to feed them with Potassium&#8230;<\/p><\/blockquote>\n<p>Forgive me for being a nerd, but&#8230;<\/p>\n<p><strong>First:<\/strong> Putting wood ash in the planting hole provides macro and microelements, primarily Calcium and Potassium. Therefore, you already had enough Potassium in your loamy soil, and you added even more with the ash.<\/p>\n<p><strong>Second:<\/strong> Blossom End Rot is treated by feeding with <em>Calcium<\/em>, not Potassium! You got them confused, and instead of Calcium, you fed them Potassium again.<\/p>\n<p><strong>Third:<\/strong> There must be significantly more Calcium in the soil than Potassium. If this balance is broken, Potassium blocks the uptake of Calcium, which your plants were already lacking!<\/p>\n<p><strong>Fourth:<\/strong> BER is most often caused by underwatering. When you water, the moisture doesn&#8217;t penetrate deep enough into the soil. I advise checking soil moisture not just on the surface, but deep down, especially in hot weather.<\/p>\n<p><strong>Fifth (Conclusion):<\/strong> I am not stating this as an absolute fact, but it is highly likely your plants were lacking Calcium, and you made the situation much worse by feeding them Potassium. The plants became incredibly weak and caught various diseases, including Cladosporium. This year, you limited the Potassium, so the plants were able to absorb Calcium properly. They became healthier and resisted the disease. Congratulations!<\/p>\n<\/div>\n<\/div>\n<div class=\"forum-post\">\n<div class=\"author-header\">\n<div class=\"forum-avatar\">V<\/div>\n<div class=\"author-meta\">\n<div class=\"author-name\">Valtwelve (Valery) <span class=\"author-stats\">\u2b50 Pro Grower (1,847 posts)<\/span><\/div>\n<div class=\"author-geo\">\ud83d\udccd Between Samara &amp; Ufa (USDA Zone 4a) | \ud83d\udcc5 September 10, 2021<\/div>\n<\/div>\n<\/div>\n<div class=\"post-content\">\n<blockquote><p><strong>Marat wrote:<\/strong><br \/>\nBy the way, I also washed my greenhouse in the fall using a pressure washer&#8230;<\/p><\/blockquote>\n<p>So two people weren&#8217;t too lazy to scrub their greenhouses, and now neither of them has Leaf Mold&#8230; Maybe I should wash mine too? The amount of willpower that must take!!!<\/p>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>\ud83d\udccc Quick Summary: The Great Calcium vs. Potassium Mix-Up \ud83c\udf45 The BER Mistake: Blossom End Rot (BER) is caused by a lack of Calcium, not Potassium. Many growers confuse the two! Feeding a plant suffering from BER with Potassium will actually make the rot much worse. \ud83d\uded1 Nutrient Lockout: Potassium and Calcium are antagonistic elements &#8230; <a title=\"Can Potassium Feeding Trigger Tomato Leaf Mold?\" class=\"read-more\" href=\"https:\/\/www.tomat-pomidor.com\/en\/can-potassium-feeding-trigger-tomato-leaf-mold\/\" aria-label=\"Read more about Can Potassium Feeding Trigger Tomato Leaf Mold?\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":5218,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[806,472],"tags":[],"class_list":["post-5218","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-grower-diaries","category-diseases-weeds"],"_links":{"self":[{"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/posts\/5218","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/comments?post=5218"}],"version-history":[{"count":2,"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/posts\/5218\/revisions"}],"predecessor-version":[{"id":5220,"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/posts\/5218\/revisions\/5220"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/posts\/5218"}],"wp:attachment":[{"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/media?parent=5218"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/categories?post=5218"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.tomat-pomidor.com\/en\/wp-json\/wp\/v2\/tags?post=5218"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}