Sumo Gardener

Fertilizing Onions In The Garden (Easy Way)

Fertilizing onions in the garden is an essential and easy gardening job that is often overlooked. Onions are a basic cooking ingredient which is cheap and simple to grow when you know how! I’m here to show you, fertilizing onions in the garden, the easy and simple way.


Onions belong to the family of plants called Alliums which includes shallots and garlic. They are an undemanding vegetable to grow that need well-drained soil. Their root systems are shallow and so they get all of their growing requirements, including nutrients, from the top surface of the soil.

Onions are heavy feeders and you need to supply their nutrients because of their shallow roots. I am going to show you how to do this. They need moderate amounts of nitrogen and higher amounts of potash and phosphate.

A little care and timely intervention with your onion crop means that you will grow onions that are of great quality and taste wonderful. By following these steps, you will have the garden and kitchen success that you deserve with your onions.

how to fertilize onions

For fertilizing onions in the garden, you will need

  • A crop of onions
  • To keep the onions free from weeds as onions don’t like to compete for nutrients and water.
  • A supply of water so that you can water the onions little and often during dry spells (Remember though that onions like free draining soil and will rot away if they get too much water!)
  • A watering can with a fine rose
  • A measuring cup or spoon
  • Onion fertilizer

There are alternative ways of fertilizing onions in the garden

You can use a chemical fertilizer. Chemical fertilizers are manufactured for different plants groups with their chemicals mixed to the right proportions for a plant group. Always buy a mix that is for root plants or onions.

Alternatively, you can use an organic fertilizer. This would involve feeding and nurturing the soil with organic materials such as rotted manure. Organic gardening is not just for onions, it is for the whole garden and is a long-term, holistic way of gardening.

My preferred method of fertilizing onions in the garden would be to use an organic fertilizer as organic gardening is better for the environment. The organic method involves a little forward planning which is achievable and produces healthy crops.

I imagine, though, that you probably require a quick feed to sustain the onions you already have growing and chemical fertilizers can do a great job. I’m going to concentrate on chemical fertilizers from now on.

So, let’s get going, here is my step by step guide to fertilizing onions in the garden



It is essential that your onion bed is free from weeds. If you have weeds amongst your onions and you apply a fertilizer you will feed the weeds and make them flourish, so you need to get to work and remove any weeds!

Carefully manoeuver your hoe between the onions to uproot the weeds. Then remove the weeds off-site. You’re onto a winner with this job as onions hate competition and removing any weeds will make your onion crop more able to get on with growth.



Remember to buy a fertilizer that’s suitable for onions or root crops. Onions need nitrogen, potash, and phosphorus in the right proportions. Nitrogen helps leaf growth, potassium helps with plant strength and vigour and phosphorus is used for healthy growth and root development.

The manufacturers of the fertilizer will mix the product to the right proportions of nitrogen, potash, and phosphorus, you simply need to follow their instructions.

In this video, Dixondale Farm talks about their onion fertilizer and describe how onions use the mix for healthy growth.



Onions need different nutrients throughout the growing season. Once you have got your onions growing you need to keep them free from weeds. Then you need to apply fertilizer every couple of weeks. You only fertilize though until the onion starts to grow its new bulbs, then stop.



You will need to read and follow the instructions for the onion fertilizer that you have bought. The manufacturer’s instructions tell you how much fertilizer to apply. Measure out your fertilizer at the recommended rate for your product.



Dixondale farm recommends sprinkling their fertilizer onto the ground. You can sprinkle the product dry straight out of the measuring cup onto the ground. Spread the fertilizer evenly along the line of the onions at the recommended rate.



Next, use your watering can and fine rose to gentle water in the fertilizer. The rose is used ‘upside down’ so the water falls out of the watering can, up into the air and then falls to the ground. This mimic’s rainfall and prevents your fertilizer from being washed away by a quick blast of water.

Go along the row of onions, following the dry mix you have already sprinkled on and given the fertilizer a good watering in. You need to apply just enough water to allow the fertilizer to be dampened and watered in, not too much. Onions don’t like to be really wet.

To finish up, here’s a video that I like that shows you how to fertilize your onions. In this video the fertilizer is mixed with water and the onions are growing in pots. This just shows you how very easy it is!

Here are some further links to help you with fertilizing onions in the garden

If you would like to go into more detail about the nutrient requirements for growing your onions, then this is a great web page which has more specific details.

If you would like to know about the organic and chemical ways to fertilize onions in the garden a detailed guide is included below. I find the information here really helpful because there is information on soil preparation before you plant and on how to fertilize your growing onions.


  • Onion fertilizer
  • All natural fertilizer for root crops

And to round up, I have included Dixondale Farm’s guide for their onion fertilizer. They recommend you use a half a cup of fertilizer for a 10-foot linear row of onions.


So, I hope you liked my, how to guide, to fertilizing onions in the garden, the easy way. It really is very simple. You need a minimal amount of equipment that you probably already have. Also following a regular program of fertilizing will result in a fantastic and tasty onion crop.

I really do like, Dixondale Farm’s comprehensive guide to growing onions. This takes you through from soil preparation to planting, growth, fertilizing and finally to a wonderful harvest. A worthwhile read.

If you enjoyed my guide to fertilizing onions in the garden that’s wonderful. I hope you are going to give your onions the fertilizer they deserve. It’s easy! If you know others who grow onions and need to know more about fertilizing them, then please share this so we can all grow great onions!

About the Author Ann Katelyn

I'm Ann Katelyn, Creator and Chief Author of Sumo Gardener. Since I was a child I've always been fascinated with plants and gardens, and as an adult this has developed into my most loved hobby. I have dedicated most of my life to gardening and started Sumo Gardener as a way to express my knowledge about gardening with the hope of helping other people's gardens thrive.

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