How To Grow Spring Onions In A Greenhouse

Popular varieties:

• White Lisbon (the most popular variety, they mature quicker and a great variety for over wintering)
• Apache (a purple skinned variety with mild flavour and crisp texture)
• Feast F1 Hybrid (ideal for summer as has good tolerance to heat)
• Guardsman (a cross between white Lisbon and a Japanese onion which is best for later sowings as it is hardy and can be overwintered)

How to plant spring onions in a greenhouse

When to plant

The benefit of growing spring onions in a greenhouse is that they can be planted pretty much all year round if you chose the correct variety. For varieties that thrive in the summer such as the Feast F1 Hybrid sow between March-August. Then varieties that do respond better in the colder months such as The White Lisbon or Guardsman you can sow in September/October onwards and over winter. For continuous supply of spring onions sow again every 3 weeks.

Preparing the Soil

Spring onions will grow and thrive in any well drained, fertile soil. So, it’s important a couple of weeks before you are planting that you mix some fertiliser into the soil and give it a rake to ensure that any of the larger lumps break down and it becomes a fine texture. Check the soil a day before you plan to plant and if the soil is very dry, water 24 hours before.

How to plant

Spring onions can either be planted in seed trays in the greenhouse for transplanting outside later, or they can be planted in a pot or tub in the greenhouse and grown there.

When planting spring onions in a tray you should opt for a tray with good drainage holes to reduce the risk of waterlogged soil. When ready, transplant out into the garden at about a 5cm spacing down the row, with rows 15cm apart. Early in the spring, cover with a cloche to speed up growth.

If you are growing in a pot in the greenhouse, sow the seeds finely over the surface and cover with about 15mm of soil. Thin out the seeds once they germinate to about 5cm apart. The pot needs to be well drained and have plenty of natural light in the greenhouse, but under cover you should be able to grow spring onions consistently all year round.

Watering

It is important that you don’t over water the spring onions as they rot in waterlogged soil. So, water sparingly just enough so that the soil is moist and not dry. If growing during the winter months water by hand as this will reduce the risk of fungal diseased as it will allow the air to keep dry in the growhouse.

Harvesting

Your spring onions should be ready for harvest roughly 8 weeks from planting. This does depend on the variety and the season in which you are growing as they may take slightly longer in the colder months. They should be around 15cm in height, once they have hit this mark, they are ready for harvest- pull them up individually by hand.

Searching for more advice on growing vegetables in a greenhouse? We have a wide range of articles to help you grow a variety of vegetables – from growing courgettes to cucumber, sweetcorn to peppers, you’re sure to find enough to keep your greenhouse well-stocked.