How to Grow Spring Onions

Green spring onions on old wooden table.

How to Grow Spring Onions

Spring onions are grown for their green immature stems and are often called bunching onions, salad onion, green onions or scallions. They are easy to grow, require very little space and can be grown all year around in your Harvst Mini Greenhouse.

Sowing

Sowing small batches every few weeks will give a continual harvest throughout the year and they are ready to harvest in just 8 weeks. Spring onion is easy to grow from seed and can be direct sown or transplanted later. It is a perfect crop to sow in your Harvst as it can stay in there till it matures or be transplanted outside. 

The ideal growing temperature is 15-21°C but spring onion seeds can cope with much colder temperatures too. It is worth noting that they take longer and are more erratic to germinate when the temperatures are cold. However, the seeds tend to germinate in around 7-14 days. 

Fill a tray with a general peat free multi purpose compost and water it. Sow the seeds roughly 1cm apart and sprinkle 1.5cm of compost on top. Press down slightly to make sure that the seeds are in good contact with the compost and carefully water again. Spring onions have shallow roots so a shallow tray can be used. 

If you’re using a modular tray then put 2-3 seeds per module and plant out as they have germinated.  

Keep the soil just moist until seeds germinate because if they dry out they will most probably not germinate at all but if the soil is waterlogged they will rot. To keep an even moisture level put a plastic dome over the tray.  As a general rule, the colder the soil the less moisture you need.

Plant care 

Keep the soil evenly moist throughout the growing season but make sure it is not waterlogged at any time. In very hot weather they may bolt but the flower stalk can be cut off and you can still eat the onion. 

Growing options 

You can choose from one of the growing options below or do a combination of 2 or 3!  Whatever option you choose, keep the soil just moist and weed free. 

  1. Grow till maturity in your Harvst: When the seedlings have emerged you can thin them a little if they are very close together. This can be done by cutting the rejects with scissors (eat them in a salad!) or carefully using a stick/pencil to loosen the soil and lift the seedling up by its leaves and transplant to elsewhere. Make sure they are big enough to handle before you set out to do this. Otherwise let them grow and harvest the closest together first
  2. Plant outside: When the seedlings have emerged and are big enough to handle they can be transplanted out into your garden. Space them 2.5cm apart. When transplanting seedlings, ideally plant out early morning or evening and/or on an overcast day. Avoid planting at peak sun times or on windy days as this can cause sun or windburn which can lead to death! 
  3. Container Grown: Spring onions grow well outside in a container and should be spaced about 2.5cm apart. 

Harvesting 

Harvest by pulling the whole plant when it has reached the required size. Usually around 8 weeks after sowing.

Watch out! 

Spring onions are generally problem free as long as you don’t overwater which can cause them to rot. 

Pro Tip

Break off any flower heads that appear.

Nerdy facts

The Botanical name for Spring onions is Allium cepa.

Recommended Varieties

Here are two great varieties but there are many more fantastic varieties to choose from!

‘White Lisbon’ matures quickly and can cope well with low temperatures 

‘Apache’ is a red variety with good flavour and a crisp texture.