Growing Tutorials

Planting early onion sets in January

Growing onions from sets

Onions have to be one of the easiest crops to grow and will reward you with delicious crisp bulbs with a homegrown flavour all their own. Onions can be grown from seed but the easiest way to cultivate them is from miniature onion bulbs or ‘sets’.

What are onions sets?
Onion sets are onions which were partially grown last year but pulled up when they reached marble size, they are then dried and stored. Onions are biennials meaning they have a 2 year lifecycle, they produce a storage bulb the fist year and flower the second. As far as onion sets are concerned they are still in their first year of growth, when planted they should just resume growing and continue to build their storage bulb.

Onions sets growing in trays in January

Planting onion sets in trays
Onions need a long growing season to ripen into the large golden globe you are hoping for so it is worth starting them off early. Onions are also photothermoperiodic (new word!) meaning they are sensitive to both temperature and day length; as late summer days get shorter they are more inclined to go to seed which is another reason get plenty of growth down early in the year.

Obviously your garden is too cold and wet to start sets off now but you can get them going in trays placed indoors towards the end of January. The onions will root and produce leaves straight away and will grow happily in a plug tray until they are planted our in March/April.

Another advantage of planting onion sets in trays is the resulting rooted and shooted plant will be less attractive to birds. Birds can be a nuisance with newly planted onion sets as they like pulling them up and throwing them around (I presume they think they are snails).

Spring planted onion sets

A word of warning
I better say this in case an early sower starts giving out to me later in the season. As I said, onions are sensitive to temperature as well as day length. If we have a warm spring followed by a cold snap early planted onions may see this as Winter passing and be more likely to run to seed. This is because they think they have entered the second year of their biennial cycle. You can avoid this problem by keeping your tray planted sets indoors until the Spring has settled.

It will also be important to plant your onions in a tray with large enough modules (I have included one below) and to harden them off gradually (leaving the trays outside during the day) in the week or two leading up to planting out. I am not saying you should plant now in trays I am just saying you can. If the weather goes your way you will have the benefit of an extra long growing season and impressively sized onions.

Either way onions sets are in and ready for dispatch, you can order today for planting now or later, it’s up to you!

Order onion sets online at quickcrop

Premium quality onion sets can be purchased from us at Quickcrop.co.uk and delivered straight to your door. This year we are stocking Turbo, Sturon, Rumba, Stuttgart and Red Karmen all of which will give you a good reliable crop. We are also stocking Red Sun and Golden Gourmet Shallots which, if you enjoy your onion flavours, are well worth growing.

  1. Lee Johnson

    My 1st year on an allotment well I got onion setts told t sow em I dis in november will let u know how I get on as just seen the really should b on shed in trays so yea all learning is it not so yea any advice for planting/ downing veg from now (10 Jan) onwards want to plant as much as poss as long as poss I’m determined it will feed me all year with a little to gove to friends I have a half plot divided in to 3

  2. Steven Turner

    I have planted onion sets in seed trays they are about 3in tall when could I plant them outside. I have them in house at the moment.

    1. Andrew

      Hi Steven. You can plant onions out in March but if they are indoors I would start to harden them off now by leaving them outside in the daytime and, after a week or two outside all the time. I hope this helps. Andrew.

    1. Andrew

      Hi Keith. Garlic is best planted in early October but you need well drained soil. Raised beds are best with a bit of poultry manure/seaweed fertiliser mixed in. I hope this helps. Andrew

  3. gerwyn thomas

    Last season i planted large onion seeds in December planted them out in march the stems were very thick inch /inch and a half but did not bulb up why?
    Pleas help i dont want to mae the same mistake again

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