Onions are heavy feeders, so they demand extra nutrients to grow healthy and big. Fertilizers pack all of the nutritional elements your veggies need to grow.
Best Fertilizer for Onions
Our Best Overall Pick
Best Ammonium Sulfate
Best Organic Fertilizer
Best Soil Additive
Best for Strong Roots
Best Earthworm Castings
Best Plant Minerals
Best Bone Meal Fertilizer
Best for Bigger Bulb
Best for Top-growth
You should first fertilize your onions when you plant them and then reapply the fertilizer every 2 to 3 weeks.
What Type of Fertilizers Are the Best for Onions?
As heavy feeders, onions rely on fertilizers for proper root and bulb formation. You should look for fertilizer high in nitrogen. When looking for the NPK ratio, choose a fertilizer with a higher N value.
The following macronutrients are essential components of an onion fertilizer:
- Nitrogen (N): It boosts the quality of bulbs with fast growth.
- Phosphorus (P): When it comes to rooting and forming bulbs, phosphorus acts as a health promoter.
- Potassium (K): Potassium is a vital nutrient for cell division and proper bulb production, adding taste.
Top 10 Best Fertilizers for Onions Reviews
We review our top 10 onion fertilizers below.
1. Jobe’s Organics 09026, Vegetable and Tomato Plant Food
Jobe’s Organics Granular Plant Food is the best fertilizer for onions. It contains microorganisms, archaea, mycorrhizal fungi & healthy bacteria. This blend improves the long-term quality of your garden soil while helping onions resist disease and repel insects. Use 1 ½ tablespoons per 2-inch plant or 1 ½ cups per 10 square feet.
Jobe’s Organics is certified 100% organic. It is a fast-acting fertilizer that helps your vegetables grow even in less-than-ideal conditions.
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2. Cesco Solutions Ammonium Sulfate Fertilizer 5lb Bag
If your goal is to lower the pH level of your soil to give your plants a little bit of acidic and healthy soil, this ammonium sulfate fertilizer is the thing for you. It has 24% Sulfur and 21% nitrogen, making this 21-0-0 fertilizer an excellent choice for your onions, tomatoes, garlic, potatoes, and other vegetables.
The ammonium sulfate in the fertilizer works excellent for lowering the pH level of the soil and making it acidic. As a result, besides onions or other vegetables, it’s an excellent choice for acid-loving flowers like azaleas, daffodils, rhododendrons, etc. You can even use this fertilizer for your lawn.
This fertilizer is water soluble, so it’s sufficient to put only 1 to 3 tablespoons per gallon of water. If you want to apply it to your lawn, 5 pounds of fertilizer will cover a 1,000 sq feet area. Simply pour in water, let it dissolve, and spray to feed your plants; it’s that easy.
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Next Read: Top 6 St. Augustine Fertilizers
3. Espoma Organic Garden-tone 3-4-4 Organic Fertilizer
Espoma Organic Garden tone is the ideal organic option for onions. It can be used to grow both cool and warm-season vegetables and herbs. It’s specially formulated to promote lush and healthy growth for onions. Plus, it doesn’t contain any nitrates, nitrites, or toxic ingredients harmful to humans or other animals.
It is a premium, organic blend of essential nutrients for the onions in your garden. It is combined with 4% phosphate, 5% calcium, and 3% nitrogen which are essential nutrients for the better growth of onion plants.
It helps your plants thrive in any season and grow an abundant harvest of delicious onions. This organic blend is derived from plant material grown without artificial pesticides or fertilizers, which is safe for humans and the environment. Espoma Organic Garden Tone doesn’t need mixing as it is a ready-to-use fertilizer.
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4. Earthborn Elements Ammonium Sulfate, Soil Additive
The soil additive from Earthborn Elements allows you to use more than one type of fertilizer in your soil. It can be added to the soil directly before planting. After spreading it in the soil, when ammonium is in contact with water, it breaks down. This helps increase the yield of your onions.
No additives or fillers have been used, so it is 100% safe for your plants and garden. Also, it is water-soluble and safe to use in all types of soil, including clay and heavy soils. You can mix the Ammonium Sulfate with water and spray the solution directly on plants. It lowers the soil’s pH level, which helps prevent soil-borne pathogens that attack plants.
Ammonium Sulfate is a natural nitrogen source, so this fertilizer’s outcome is fresh and healthy onions.
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5. Down to Earth Organic Bone Meal Fertilizer
Down to Earth organic bone meal fertilizer is an excellent organic fertilizer sourced from bone meal and is ideal for early crop production for onions that have been ground up to ensure a high level of nutrients. This fertilizer contains 15% phosphorus, 18% calcium, and 3% nitrogen.
It also improves the growth of young seedlings and encourages stronger root development for more vigorous plants that can withstand the stresses of growing in poor soil. It is a non-invasive organic fertilizer that is 100% natural and non-toxic.
Bone meal has been used as a natural fertilizer for centuries. This organic fertilizer enhances root development, and early season growth, and boosts fruiting in your plants. It is excellent for your garden or farm and will help you grow the best onion plants.
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6. Worm Castings Organic Fertilizer, Wiggle Worm Soil Builder
The Worm Castings Organic Fertilizer contains pure earthworm castings, which are the end product of worm digestion. These nutrient-rich castings are very good for your soil and the health of your indoor and outdoor plants.
This odor-free fertilizer is excellent for your soil because it improves soil structure and water retention. It’s beneficial for growing onions because it protects your onion plants from certain root diseases. It also improves seed germination and onion production.
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7. Lilly Miller Morcrop Vegetable Food 5-10-10
Lilly Miller Morcrop Plant Food is a slow-release fertilizer that feeds your onions steadily for up to six weeks after just one application.
Its ready-to-use formula contains natural ingredients fortified with a blend of essential nutrients. It does not need to be mixed with water, so you can apply it directly to your soil. Water your onions after fertilizing.
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8. Burpee Bone Meal Fertilizer for Bulbs
The Burpee bone meal fertilizer is an excellent food for onions. You can use it to provide organic nitrogen, phosphorus, and calcium. It is ground finely and blends in with the soil slowly but effectively.
Bone meal breaks down slowly and releases nitrogen that enhances the rich growth of the plants. It provides all the vital nutrients for onions, which is an integral part of the nutrient cycle. The phosphorus helps your plants to grow strong roots that will produce delicious vegetables.
The best use of this fertilizer is to add it to the soil before harvesting. Also, the Burpee fertilizer is OMRI Listed for Organic Gardening. Instead of onions, you can also use these for other vegetables like tomatoes, peppers, etc.
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9. Miracle-Gro Water Soluble All Purpose Plant Food
Miracle-Gro Water Soluble All Purpose Plant Food is great if your onions need instant nutrition. This fertilizer has a high percentage of nitrogen which will help your onion bulbs grow bigger and faster. Since it feeds your onions a lot of nutrients quickly, you will need to reapply every 7 to 14 days.
It is simple to apply. Mix a tablespoon of this plant food for every gallon of water and then pour over your onions every 1 to 2 weeks.
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10. Osmocote Smart-Release Plant Food
Osmocote Smart-Release is specially formulated to give onion plants an early season start, with strong root development and top-growth. It has resin that is semi-permeable and covered with nutrition granules, and the coating helps water to dissolve all the nutrients into the root zone of the plant.
It is formulated to give strong root development, which helps plants get off to a strong start during their first season. It contains 14% nitrogen and 14% phosphorus for the healthy growth of onions which are the most necessary nutrients.
Osmocote plant food starts to show results in just a few weeks. Once used, it will keep flourishing for the next four months. Its dissolving process is slower to help the soil collect the nutrients for plants for a long time.
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