{"id":1989,"date":"2026-11-03T07:00:00","date_gmt":"2026-11-03T06:00:00","guid":{"rendered":"http:\/\/192.168.60.121\/?p=1989"},"modified":"2026-11-04T16:55:01","modified_gmt":"2026-11-04T15:55:01","slug":"yellow-leaves-diagnosis","status":"publish","type":"post","link":"https:\/\/ortoinbalcone.com\/en\/yellow-leaves-diagnosis\/","title":{"rendered":"Yellow Leaves: the 5-Step Diagnosis"},"content":{"rendered":"<p>Yellow leaves are the most common signal in the balcony garden. And the most misunderstood: most of the time <strong>it is not a disease<\/strong>, it is a message. The classic mistake is rushing for the fungicide, when the plant is actually saying &#8220;too much water&#8221; or &#8220;I am missing nitrogen&#8221;.<\/p>\n<p>This guide gets you to the cause in 5 steps, in this order: <strong>observe first, act second<\/strong>. If you skip steps 1\u20133 and go straight to the fertiliser, you risk making things worse.<\/p>\n<p><strong>The golden rule<\/strong>: a uniform, slow yellowing almost always has a nutritional or water cause. Sudden yellowing, in patches or with spots, points to a different problem (pests, disease). In that case go straight to <a href=\"\/en\/problems-pests-and-diseases\/\">Problems, Pests and Diseases<\/a>.<\/p>\n<h2>Step 1: Where is it yellow?<\/h2>\n<p>The <em>where<\/em> tells you much more than the <em>how much<\/em>.<\/p>\n<ul>\n<li><strong>The low, old leaves dry first<\/strong>: nitrogen deficiency, the nutrient the plant moves &#8220;from old leaves to new leaves&#8221;. It is the most widespread signal in pots.<\/li>\n<li><strong>The new leaves come out pale, almost whitish<\/strong>: iron deficiency (iron chlorosis). Iron is not mobile in the plant: do the old leaves give it to the new ones? No \u2014 the opposite, the new ones stay pale.<\/li>\n<li><strong>Everything in patches, with brown tips<\/strong>: almost always water, not fertiliser. Go to step 2.<\/li>\n<\/ul>\n<p>If you stop here you already have 60% of the diagnosis done.<\/p>\n<h2>Step 2: The water (cause no. 1 in pots)<\/h2>\n<p>The pot has an advantage and a flaw: the advantage is that you control it, the flaw is that <strong>there is no margin for error like in the ground<\/strong>.<\/p>\n<p>Two opposite mistakes, same symptom:<\/p>\n<ol>\n<li><strong>Too much water<\/strong> (the most frequent): the substrate stays sodden, the roots cannot breathe, they rot slowly. The leaves yellow, sometimes with soft tips. Stick in your finger: if at 2\u20133 cm the substrate has been waterlogged for days, you found the cause. The solution is not &#8220;water less&#8221;: it is <strong>drainage and air<\/strong> (see <a href=\"\/en\/watering-in-containers\/\">Watering in containers<\/a> and <a href=\"\/en\/substrate-and-drainage\/\">Substrate and drainage<\/a>).<\/li>\n<li><strong>Chronically dry substrate<\/strong>: rarely the main cause of yellow leaves \u2014 more often it produces rolled leaves and dry tips \u2014 but in winter, with watering halved, it happens.<\/li>\n<\/ol>\n<p><strong>Practical test<\/strong>: take the plant out of the pot (or stick a long stick in). White roots = healthy. Brown, soft roots = rot in progress: in this case you act on the drainage and, if it is serious, on repotting.<\/p>\n<h2>Step 3: The veins (the iron trick)<\/h2>\n<p>Turn the leaf and look at the <strong>veins<\/strong>:<\/p>\n<ul>\n<li><strong>Yellow with well-green veins<\/strong> = iron chlorosis. The blade is pale, the vein network stays green: a sharp contrast. It happens especially on alkaline substrates (high pH) or chalky ones, where the iron is there but the plant cannot absorb it.<\/li>\n<li><strong>Uniform yellow, veins included<\/strong> = it is not iron. Back to steps 1\u20132 or move on to 4.<\/li>\n<\/ul>\n<p>For iron chlorosis the cure is <strong>chelated iron<\/strong>, which stays available at the substrate&#8217;s pH: <a href=\"https:\/\/www.amazon.it\/dp\/B0D45Z3R5R?tag=ortoinbalcone09-21\" rel=\"sponsored nofollow noopener\" target=\"_blank\">LERAVA chelated iron 200 g<\/a> dissolves in water and is used both as cure and prevention (1 dose a month in spring\u2013summer). If the substrate is chalky and the problem recurs every year, the real fix is to change the substrate (see <a href=\"\/en\/substrate-and-drainage\/\">Substrate and drainage<\/a>), not just to supplement.<\/p>\n<h2>Step 4: Nitrogen (and how much to feed)<\/h2>\n<p>If the old leaves yellow uniformly and the water is regular, you are missing <strong>nitrogen<\/strong>: the element that drives growth and green foliage.<\/p>\n<p>The potting rules:<\/p>\n<ul>\n<li>Leafy vegetables (lettuce, spinach, arugula) are &#8220;greedy&#8221; for nitrogen: feed every 2\u20133 weeks, not every month.<\/li>\n<li>Granular slow-release fertiliser doses itself: a <a href=\"https:\/\/www.amazon.it\/dp\/B0CMJFQGP3?tag=ortoinbalcone09-21\" rel=\"sponsored nofollow noopener\" target=\"_blank\">slow-release fertiliser for the garden<\/a> is sprinkled on the substrate and works for 6\u20138 weeks.<\/li>\n<li>In winter (below 8\u201310 \u00b0C) <strong>you stop<\/strong>: below that threshold the roots do not absorb, and accumulated fertiliser salinises the substrate.<\/li>\n<\/ul>\n<p>The full table with doses per crop is in <a href=\"\/en\/feeding-plants-in-pots\/\">Feeding plants in pots<\/a>.<\/p>\n<p><figure><img decoding=\"async\" src=\"\/wp-content\/uploads\/2026\/10\/04-inline.webp\" alt=\"Two lettuce leaves for comparison on the edge of a pot: one healthy and bright green\" loading=\"lazy\" \/><\/figure>\n<\/p>\n<h2>Step 5: Salts and substrate<\/h2>\n<p>Two &#8220;underlying&#8221; causes that show up after months:<\/p>\n<ul>\n<li><strong>Salt build-up<\/strong>: watering only with hard tap water, or overfeeding, leaves white crusts on the surface. The substrate becomes salty and burns the roots. Cure: a generous flush watering (and every spring, changing 30\u201350% of the substrate).<\/li>\n<li><strong>Exhausted substrate<\/strong>: after 2\u20133 seasons in the same pot, the compost compacts and holds neither water nor air anymore. You see it: water runs off the surface without entering. Cure: repot, or at least a surface replacement.<\/li>\n<\/ul>\n<h2>When yellow leaves are a disease<\/h2>\n<p>Some patterns are not nutritional:<\/p>\n<ul>\n<li><strong>Yellow-brown spots that spread quickly<\/strong>, especially after rains or evening sprays: downy mildew (classic on lettuce and courgette).<\/li>\n<li><strong>Leaves that yellow and drop within hours of being touched<\/strong>: watch for powdery mildew or virus \u2014 virus is not curable, the plant is removed.<\/li>\n<li><strong>Leaflets curling upwards with pale dots<\/strong>: aphids that have been sucking. It is solved with water and Marseille soap (5 ml\/l).<\/li>\n<\/ul>\n<p>The full diagnosis with comparison photos is in <a href=\"\/en\/problems-pests-and-diseases\/\">Problems, Pests and Diseases<\/a>.<\/p>\n<h2>Table: quick diagnosis<\/h2>\n<table>\n<thead>\n<tr>\n<th>Where it is yellow<\/th>\n<th>Veins<\/th>\n<th>Probable cause<\/th>\n<th>First cure<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Old leaves, uniform<\/td>\n<td>pale<\/td>\n<td>Nitrogen<\/td>\n<td>Feed<\/td>\n<\/tr>\n<tr>\n<td>New leaves, almost white<\/td>\n<td><strong>green<\/strong><\/td>\n<td>Iron (chlorosis)<\/td>\n<td>Chelated iron<\/td>\n<\/tr>\n<tr>\n<td>Everything, in patches, soft tips<\/td>\n<td>\u2014<\/td>\n<td>Too much water<\/td>\n<td>Drainage<\/td>\n<\/tr>\n<tr>\n<td>Uniform + white crusts<\/td>\n<td>\u2014<\/td>\n<td>Salts in the substrate<\/td>\n<td>Flush + change<\/td>\n<\/tr>\n<tr>\n<td>Fast brown spots<\/td>\n<td>\u2014<\/td>\n<td>Disease (downy mildew)<\/td>\n<td>See disease guide<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h2>Sources<\/h2>\n<ul>\n<li>CREA \u2014 Fertilising and nutritional deficiencies in vegetable crops (technical sheets)<\/li>\n<li>Cornell University \u2014 Yellow Leaves: causes and corrections (diagnostic guide for water and nutritional causes)<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Yellow leaves are the most common signal in the balcony garden. And the most misunderstood: most of the time it is not a disease, it is a message. The classic mistake is rushing for the fungicide, when the plant is actually saying &#8220;too much water&#8221; or &#8220;I am missing nitrogen&#8221;. This guide gets you to [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":1748,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_locale":"en_GB","_original_post":"https:\/\/ortoinbalcone.com\/?p=1852","oib_translation_group_id":"","oib_affiliate_link_limit":0,"footnotes":""},"categories":[2],"tags":[],"class_list":["post-1989","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-guide","en-GB"],"_links":{"self":[{"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/posts\/1989","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/comments?post=1989"}],"version-history":[{"count":2,"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/posts\/1989\/revisions"}],"predecessor-version":[{"id":2344,"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/posts\/1989\/revisions\/2344"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/media\/1748"}],"wp:attachment":[{"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/media?parent=1989"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/categories?post=1989"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ortoinbalcone.com\/wp-json\/wp\/v2\/tags?post=1989"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}