Onion Nutrient Deficiency: Signs, Causes and the Fertilizer That Fixes It
Onion nutrient deficiency is one of the first things to check when the leaves of your sibuyas (onion) turn yellow, purple or burnt at the edges. On Philippine farms the usual ones are nitrogen, sulfur, potassium, phosphorus, zinc, boron, magnesium, copper and manganese. This guide shows where each one starts, how to be sure, and the fertilizer that fixes it.
Start with one question: did the change begin on the old leaves or on the young ones? Nitrogen, potassium, phosphorus and magnesium move inside the plant, so a shortage shows on the old, lower leaves first. But sulfur, zinc, boron, copper and manganese stay where the plant first put them, so the young leaves and the growing tip show it first. After that, the color and the pattern narrow down which onion nutrient deficiency you have, and a soil test confirms it. Each one below has its signs, its causes and its fix.
Onion nutrient deficiency signs, old leaves and young leaves
Shows first on the old leaves
| Nutrient | Where it starts | What you see | Fix with |
|---|---|---|---|
| Nitrogen | old, lower leaves, the whole plant | Pale, stiff, upright leaves that yellow and die back from the tips, and small bulbs. | Urea 46 0 0, Ammonium sulfate 21 0 0 |
| Potassium | old, lower leaves, leaf edges and tips | Leaves first turn darker green, then the tips of older leaves wilt, droop and turn papery. | Muriate of potash 0 0 60, Sulfate of potash 0 0 50 |
| Phosphorus | old, lower leaves | Slow, dull green plants whose leaf tips die back without yellowing, and many thick necked bulbs. | 16 20 0, Diammonium phosphate 18 46 0 |
| Magnesium | old, lower leaves | Older leaves turn evenly yellow along their whole length, with white tips. | Epsom salt / magnesium sulfate, Dolomite |
Shows first on the young leaves
| Nutrient | Where it starts | What you see | Fix with |
|---|---|---|---|
| Sulfur | young leaves and the tip, the whole plant | Young leaves turn evenly yellow, plants are thin and spindly, and bulbing is late. | Ammonium sulfate 21 0 0, Single superphosphate 0 20 0 |
| Zinc | the whole plant, young leaves and the tip | Stunted plants with twisted, bent leaves and faint yellow stripes. | Zinc sulfate |
| Boron | young leaves and the tip, fruit, grain or tubers | Brittle, bluish green, distorted leaves with yellow cross lines and cracks near the base. | Borax |
| Copper | fruit, grain or tubers, leaf edges and tips | Bulb scales are thin and pale yellow, bulbs are soft, and leaf tips burn. | Copper sulfate |
| Manganese | old, lower leaves, between the veins | Older leaves yellow between veins, tips burn and curl, and bulbs have thick necks. | Manganese sulfate |
Before you buy fertilizer for a onion nutrient deficiency
So use the table to pick the likeliest onion nutrient deficiency, then read its section below. Also keep in mind that dry soil, standing water, cold nights, a pest or a disease can look the same. That is why it pays to check the roots and the whole field first.
Nitrogen deficiency in onion
Plants stay short. The leaves fade from pale green to yellow, stand stiff and upright, and die back from the tips, the older leaves first. Bulbs stay small and mature early, and the neck tissue above the bulb turns soft at maturity. You see it most at this stage: from transplanting to the start of bulbing.
Why nitrogen deficiency happens in sibuyas
Sandy soils, heavy rain or irrigation that washes nitrogen out, and too little fertilizer.
How to tell it apart
Sulfur deficiency yellows the young leaves first. Potassium deficiency first makes leaves darker, with wilting tips. To be sure, soil test before planting. Send the tallest leaf for a tissue test before bulbing. Check that the oldest leaves yellowed first.
What to apply for nitrogen deficiency
Dry bulb onions need 200 to 300 kg N per hectare. Put about a quarter in before planting, then split the rest every 10 to 14 days for 2 to 2.5 months. For quick help give a 1 percent urea (10 g per liter, 160 g in a 16 liter sprayer) or 2 percent DAP spray (320 grams in a 16 liter sprayer) twice, a week apart. Many onion growers already apply more than 120 kg N per hectare. So check your rate before adding more.
- Urea 46 0 0
- Ammonium sulfate 21 0 0
- Complete 14 14 14
- Diammonium phosphate 18 46 0
Sold here with nitrogen: Atlas Granular Urea (46 0 0) by Atlas Fertilizer, Crown Champion Ammonium Sulfate by Aqua Hydroponic Prime Ventures (21 0 0 with 24 percent sulfur), Agripower 46 0 0 (Locally Blended) Coated by Green Acres Agri Tech and Calcipro by Ramgo (15.5 0 0 with 18.8 percent calcium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to urea fertilizer, and the page on nitrogen deficiency in every crop. In anee.io, Anee, the smart farm technician, reads a photo of the leaf and tells you which nutrient is short.
To keep it away, split nitrogen and stop before bulbing ends. Too much or too late nitrogen slows maturity and leaves soft bulbs that rot in storage. Let a soil test and the crop's color set the season's nitrogen.
Sulfur deficiency in onion
The young leaves turn evenly yellow first, then the whole plant. Plants are thin, weak and spindly, and bulb formation and maturity are delayed. Bulbs are less pungent. You see it most at this stage: before bulbing.
Why sulfur deficiency happens in sibuyas
Sandy soils low in organic matter, sulfur free fertilizers such as urea and 14 14 14 used for years, and burning crop waste.
How to tell it apart
Nitrogen deficiency starts on the older leaves. Iron deficiency yellows the youngest leaves completely but is rare. To be sure, soil and leaf test for sulfur. In a soil test, less than 10 ppm of sulfate sulfur is low.
What to apply for sulfur deficiency
Give 45 to 70 kg of sulfur per hectare in two halves, one at planting or transplanting and one before bulbing. On sulfur poor soil, 40 kg of sulfur per hectare as Ammonium sulfate 21 0 0 or single superphosphate with the usual NPK raised aggregatum onion yield by about a quarter. You can also use sulfur dust, about 25 kg per hectare.
- Ammonium sulfate 21 0 0
- Single superphosphate 0 20 0
- Gypsum
Sold here with sulfur: Crown Champion Ammonium Sulfate by Aqua Hydroponic Prime Ventures (21 0 0 with 24 percent sulfur), Philphos Gypsum (22.2 percent calcium and 17.4 percent sulfur), Harvester Sulphate of Potash by Universal Harvester (0 0 50 with 17.5 percent sulfur) and Agsmart Kieserite Granule (20 percent sulfur and 16.3 percent magnesium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to ammonium sulfate fertilizer, and the page on sulfur deficiency in every crop.
To keep it away, keep a sulfur source such as ammonium sulfate in every crop. Keep sulfur in the feeding plan even on rich soils. Test the soil every two or three years.
Potassium deficiency in onion
Foliage first turns darker green, then the tips of the older leaves wilt, especially on the upper side. Leaves droop, turn satiny and then papery, and yellow like nitrogen deficiency. Tip burn and early bolting are common, and bulbs stay small. You see it most at this stage: bulb development.
Why potassium deficiency happens in sibuyas
Sandy soils, soils cropped for years without potash, and heavy nitrogen without potash.
How to tell it apart
Nitrogen deficiency gives pale, not dark, leaves at first. Purple blotch disease gives purple spots with rings. To be sure, soil test for potassium. Tissue test of the tallest leaf.
What to apply for potassium deficiency
Put 30 to 50 percent of the potash in before planting and the rest while the bulbs grow, for bigger bulbs. Give a 1 percent potassium sulfate spray (10 g per liter, 160 g in a 16 liter sprayer) twice, a week apart. A usual dose is 1 to 2 bags of Muriate of potash 0 0 60 per hectare, half before transplanting and half when bulbs start to form.
- Muriate of potash 0 0 60
- Sulfate of potash 0 0 50
- Potassium nitrate 13 0 46
Sold here with potassium: Atlas Muriate of Potash (MOP) by Atlas Fertilizer (0 0 60), Simplot Sulfate 0 0 50 by Nutranta, Potassium Nitrate by Parafield (13 0 46) and Qrop Mix Production 14 0 23 plus 13 Cao by Farmtech Agriland (14 0 23 with 9.3 percent calcium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to potash fertilizer, and the page on potassium deficiency in every crop.
To keep it away, split potash and keep the soil pH above 6. Test the soil every two or three years. Keep organic matter up with compost, manure or crop residues.
Phosphorus deficiency in onion
Growth is slow and maturity late. Leaves turn a dull green and die back from the tips without the yellowing seen in nitrogen or potassium shortage, and some tips turn reddish. Many bulbs have thick necks or fail to form. You see it most at this stage: seedling to early bulbing.
Why phosphorus deficiency happens in sibuyas
Acid and volcanic soils, cold soils, and fields where the soil fungi that help onion take up phosphorus are few, such as after fumigation.
How to tell it apart
Manganese deficiency also gives thick necks but with yellow between veins of older leaves. To be sure, soil test: keep available P at about 25 ppm.
What to apply for phosphorus deficiency
Add 1 kg of phosphorus per hectare for every 1 ppm the soil test is below 25 ppm. For a standing crop give a 2 percent DAP 18 46 0 spray (20 g per liter, 320 g in a 16 liter sprayer) twice, 15 days apart.
- 16 20 0
- Diammonium phosphate 18 46 0
- Single superphosphate 0 20 0
- Complete 14 14 14
Sold here with phosphorus: Philphos 18 46 0 (Di Ammonium Phosphate), Atlas Super Gro (16 20 0) by Atlas Fertilizer, Amigo Planters Granular Single Super Phosphate by La Filipina (0 18 0 with 11 percent sulfur) and Triple Super Phosphate by Newman Chemicals (0 46 0). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to 16 20 0 fertilizer, and the page on phosphorus deficiency in every crop.
To keep it away, apply phosphorus at planting, and add organic matter that feeds the root fungi.
Zinc deficiency in onion
Growth is restricted and leaves twist and bend, with yellow streaks and faint yellowing between the veins. Onion is very sensitive to zinc shortage. You see it most at this stage: early growth.
Why zinc deficiency happens in sibuyas
Soils above pH 6.5, over limed soils and heavy phosphorus. Onion is one of the crops with the highest zinc need.
How to tell it apart
Herbicide injury also twists onion leaves. Check spray records. To be sure, soil test for zinc and a leaf test. In a soil test, less than 0.8 ppm of zinc is low.
What to apply for zinc deficiency
Give 6 kg of zinc per hectare in the basal fertilizer only when a soil test confirms the shortage, since too much is toxic. For a standing crop give a 0.5 percent zinc sulfate spray (5 g per liter, 80 g in a 16 liter sprayer) twice, 15 days apart.
- Zinc sulfate
Sold here with zinc: Harvester Zinc Sulphate Heptahydrate by Universal Harvester (22 percent zinc), Tierramino ZN by Unilox Far East Resources (7 0 0 with 10 percent zinc), Semia by SCL Filipinas (20 percent zinc) and Omex Zynergy by Jardine Distribution (3.8 percent zinc and 2.1 percent copper). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to fertilizer with zinc, and the page on zinc deficiency in every crop.
To keep it away, test for zinc before planting on high pH soils. Do not overdo phosphorus.
Boron deficiency in onion
Plants grow distorted and stunted. Leaves turn brittle and grey green to blue green, young leaves mottle yellow green. Older leaves die back from the tip with sunken areas. Yellow lines across the leaf near the base turn into cracks, and bulbs can crack or split. You see it most at this stage: leaf growth to bulbing.
Why boron deficiency happens in sibuyas
Sandy soils low in organic matter, high pH soils and dry spells.
How to tell it apart
Calcium deficiency also kills leaf tips but without the cross cracks. To be sure, soil test for boron. In a soil test, less than 0.5 ppm of boron is low.
What to apply for boron deficiency
Give 1 kg of boron per hectare (about 9 kg Borax) mixed in before transplanting or sowing when the soil test is low. Do not go over 1 kg of boron per hectare. Give about 10 kg Borax per hectare to the soil, or a borax spray of 1 g per liter (16 g in a 16 liter sprayer).
- Borax
Sold here with boron: Etifert 11 (Borax Decahydrate) by Zetryl Chem (11 percent boron), Fertibagra 15G by Unilox Far East Resources (14.6 percent boron), B17 (Boric Acid) by Newman Chemicals (17 percent boron) and Better Yield by Bacphil Planters Fertilizer (0 0 0.9 with 10 percent boron). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to foliar fertilizer, and the page on boron deficiency in every crop.
To keep it away, test before adding boron. Onion is easily hurt by too much. Keep organic matter up with compost, manure or crop residues.
Magnesium deficiency in onion
Growth slows and older leaves turn evenly yellow along their whole length. Leaf tips may turn white and irregular oval patches form on the leaves. You see it most at this stage: mid season.
Why magnesium deficiency happens in sibuyas
Acid sandy soils and heavy potash.
How to tell it apart
Nitrogen deficiency yellows the leaves too, but from the tips with stiff upright leaves. To be sure, soil test for magnesium.
What to apply for magnesium deficiency
When the soil is low, give 30 kg of magnesium per hectare before planting. Give a 0.5 percent magnesium sulfate spray (5 g Epsom salt per liter) twice, a week apart. Give about 80 kg magnesium sulfate per hectare in bands near the plants.
- Epsom salt / magnesium sulfate
- Dolomite
Sold here with magnesium: Dolomite by A6 Agrisource (24 percent calcium and 11 percent magnesium), Agsmart Kieserite Granule (20 percent sulfur and 16.3 percent magnesium), DDDD Planter's Choice Magnesium Sulphate Monohydrate by Modern Time (15.1 percent magnesium) and Zetryl MAG 9 by Zetryl Chem (9 percent magnesium). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to complete fertilizer, and the page on magnesium deficiency in every crop.
To keep it away, use dolomite on acid soils. Test the soil every two or three years. Lime acid soil with Dolomite rather than plain lime.
Copper deficiency in onion
Bulb scales are thin and pale yellow and the bulbs lack firmness, maturing early. Leaves show tip burn with a mottled yellow look. You see it most at this stage: bulbing.
Why copper deficiency happens in sibuyas
Peat and other high organic matter soils, mostly when acid. Onion has a high copper need.
How to tell it apart
Potassium deficiency also burns tips, without the pale thin scales. To be sure, soil test for copper on peat or muck soils. In a soil test, less than 0.2 ppm of copper is low.
What to apply for copper deficiency
Give a 0.3 percent copper sulfate spray (3 g per liter, 48 g in a 16 liter sprayer) twice, a week apart. For the soil, band about 2 to 4.5 kg of copper per hectare beside the onion rows. Stop when the total reaches about 34 kg of copper per hectare, so it does not build up to a toxic level.
- Copper sulfate
Sold here with copper: Grower's Choice Copper Sulphate Pentahydrate by Zetryl Chem (25 percent copper and 12 percent sulfur), Liquid Chelate Copper with Sulfur by Sagrex (5 percent copper and 2 percent sulfur), Omex Zynergy by Jardine Distribution (3.8 percent zinc and 2.1 percent copper) and Cambiar Lsa Combi by Donato C. Cruz (2 percent manganese, 1 percent zinc and 0.5 percent copper). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to foliar fertilizer, and the page on copper deficiency in every crop.
To keep it away, follow the soil test. One dose lasts 5 to 8 years. Never repeat copper without a test: it stays in the soil for years.
Manganese deficiency in onion
Growth is slow and maturity late. Older leaves yellow between the veins, then tips burn, leaves curl and die. Bulbing is delayed and many bulbs have thick necks. You see it most at this stage: before and during bulbing.
Why manganese deficiency happens in sibuyas
High pH and over limed soils, and soils high in organic matter. Onion needs a lot of manganese.
How to tell it apart
Phosphorus deficiency also gives thick necks but leaves are dull green without the yellow between veins. To be sure, leaf test for manganese and a soil pH test. In a soil test, less than 1 ppm of manganese is low.
What to apply for manganese deficiency
Give a 0.3 percent manganese sulfate spray (3 g per liter, 48 g in a 16 liter sprayer) twice, 15 days apart. Feed about 5.6 kg of manganese per hectare to the soil, or spray 1.1 kg per hectare.
- Manganese sulfate
Sold here with manganese: Manganese Sulfate by Zetryl Chem (31 percent manganese), Turan by SCL Filipinas (11 percent manganese, 6 percent zinc and 2.8 percent copper), Tierramino MN by Unilox Far East Resources (7 0 0 with 12 percent manganese) and Multimate by Agway (4 0 0 with 4.5 percent sulfur, 2.8 percent zinc and 1.8 percent manganese). Check the FPA registration on the bag and follow the label rate. For the how and when, see our guide to foliar fertilizer, and the page on manganese deficiency in every crop.
To keep it away, do not over lime onion fields. Test the soil every two or three years.
A soil test is the surest check for any onion nutrient deficiency. Before you buy, ask your Municipal Agriculture Office where to send a soil sample. The DA regional soil laboratories test soil, and the result says how much of each fertilizer your sibuyas needs. That saves money, because extra fertilizer is money lost.
Open the Nutrient Deficiency Finder, pick sibuyas, say where the leaves changed first and what you see, and get the fertilizers sold here that fix it.
- Anee, the smart farm technician, reads a photo of the leaf
- The cropping calendar dates every fertilizer application of your season
Onion nutrient deficiency questions
Why are my sibuyas leaves turning yellow?
What fertilizer fixes nitrogen deficiency in onion?
What fertilizer fixes sulfur deficiency in onion?
What fertilizer fixes potassium deficiency in onion?
How do I know which nutrient my sibuyas lacks?
Find the missing nutrient and fix it
With Libre + Anee, read the whole guide: how to tell the deficiency from look alikes, how to be sure, what to apply, and the fertilizers sold here that supply it.
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