Growing Onions and Shallots in a Greenhouse

Onions and shallots are among the most versatile forms of vegetables to grow at home. If you’re thinking of having a go at growing your own produce, then here are some tips and advice on growing onions and shallots in a greenhouse.

How To Grow Onions and Shallots

Both onions and shallots can be grown from either seed or sets. One of the easiest ways, and especially so for new greenhouse growers, is to begin by growing them from sets. Onion sets are beneficial as they do well in all conditions, even cold greenhouses, and are more resilient against pests and diseases.

To the uninitiated, an onion or shallot set is basically a mini bulb – a bit like a small onion or shallot. The fat end is put down into the soil and the tip remains just above the top of the soil. A variety of onions and shallots are available to purchase as sets and, although they’re slightly more expensive to buy than seed, they’re definitely better to start off with.

Onion sets are best planted from mid-March to mid-April and should be planted in rows, with about 8 inches between each row. Shallot sets are best planted from mid-February to mid-March and should be similarly placed.

If you decide to give onion or shallot seed a go, then onion seed should be sown from late February to early April, and shallot seed from March to April. Seeds should be sown in rows in your greenhouse, either in raised beds or in trays, with spaces of approximately 8in between each row. Each seed should produce a single onion or shallot and, as the seedlings grow you can thin them out.

Caring For Onions and Shallots

Once your onions and shallots are planted in your greenhouse, they’ll need to be watered regularly, especially if the weather is dry. If you spot any flower spikes growing, then remove these as soon as possible, as you don’t want flowers growing.

It’s best to stop watering the plants when the onions or shallots have swollen up in size. At this point, it’s also advisable to brush back any soil surrounding the top of the them, so that the bulb can get the benefit of extra sunlight.

If you’re not averse to using fertiliser, a general purpose fertiliser will help ensure that all the essential nutrients are present. Some gardeners suggest that a low potash fertiliser is good if you’d prefer to produce smaller and tastier onions.

When they’re grown outside in the garden, one of the biggest hazards is that birds will grab hold of the tip of the onion or shallot and pull them out of the ground, but thankfully when they are grown inside a greenhouse, you shouldn’t have this problem.

When To Harvest Onions and Shallots

The best way of knowing when the time is right to start harvesting your home grown onions and shallots is when you notice that the outer foliage is beginning to turn yellow or when it begins to droop over. This often happens from about July, especially for shallots.

Once harvested, the produce can be dried, then stored or used. If kept in a cool dark place, they can store well for up to 12 months.

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