'You'll never need to buy onions again' – expert shows how to grow the essential ingredient using leftovers

Sure, they might cause us to shed a tear, but who doesn’t love an onion? Crunchy, flavourful and the perfect starting ingredient for many classic dishes.

Garden writer Simon Akeroyd, who has shown us how to grow thyme for free, has now revealed we can do the very same thing with onions. And while they are fairly inexpensive, it saves you adding them to the food shop each week, plus it's a great way to reduce waste and practise sustainable gardening ideas.

So next time you’ve sliced your onions and were planning to toss the remainders in your homemade compost pile – don’t. This incredibly simple method is all you need to begin growing vegetables from scratch, producing new shoots in less than 2 weeks. This genius plan will start you on your journey to sow all the onions you’ll ever need.

It really is so simple, too. Once you’ve chopped your onions (and dried your tears as a result), keep the thicker, coarser base that you wouldn’t normally add to your recipes. This is the bit which will have some stringy roots coming out of it – and this is what you want.

You then take this base cutting and place it in a small dish of shallow water. Simon initially leaves his cutting in something as cheap and easy as the lid of a jar just filled with water.

Leave this for a few days and when it starts to grow new roots and shoots, plant it in some compost. In just one week’s time, you’ll see the onion starting to grow new stems.

You can use these stems as they are – red onion shoots can be used similarly to chives, a little culinary sprinkling that elevates stir-fries, soups, salads or even sandwiches. If you are going to do this, make sure you leave some of the shoots alone if you want to regrow actual onion bulbs.

Once you’ve left the shoots to flower and set seed, you can collect the seed and sow it.

According to the RHS, sowing onion seeds can be done indoors or outside, from mid-winter to mid-spring. However, it’s not the right time to sow onions outdoors, as these need to be done when the soil starts to warm up.

To make the most of this trick as we head into the colder months, you can use Nancy Birtwhistle’s trick and use a homemade, upcycled propagator as you do this. With this, sow your seeds about half an inch deep into your trays filled with peat-free seed compost.

The RHS advises one seed per module is effective, but it's also possible to sow three or four seeds per module, although the resulting bulbs are likely to be smaller.

Place the tray in a heated propagator or on a warm sunny windowsill. Seedlings should appear within a couple of weeks. Remove from the propagator, place in bright light and keep the compost slightly moist. Harden off indoor-sown plants before planting into prepared ground.