How I Sow and Grow Onions

Over the years, I've tried various ways of growing onions before settling on this method.  I've tried direct sowing, growing from sets, early sowing, late sowing and various other combinations that apparently worked for others.  This is the most successful for me though.  Each year, we've also tried different varieties ranging from Red Brunswick to White Globe, but the firm favourites are easily Ailsa Craig and Bedfordshire Champion.  The have been solid producers and both varieties store well, beating anything you'll get in a supermarket, hands down.  Let's take a look...

Sowing from seed has always been the most reliable method for me.  Rarely have I had onions grown from seed bolt.  Neither have I had any issues with white rot with these varieties.  Some people say that there's no need to give onion seeds any heat to germinate, and that might well be true but on the back of a seed packet for Bedfordshire Champion for example, it says about giving them a bit of heat for germination.  That advice is there for a reason, so I tend to follow it!

Onions, like many of my seeds, start off in 1/4 sized seed trays.  I fill them with my normal seed mix and then press down with a small wooden tamping tool I have made.  This ensures that the seed has good contact with the compost it's sown in.

Once the seed trays are prepared, I scatter the seeds reasonably thinly onto the compost.  As the seeds grow, they tend to send down one or two main roots in their early stages, so it's best if each seed has a bit of space to try and prevent the roots from tangling too much.

Next, I finish off the sowing by topping up the try with more seed mix, patting it down gently and then spraying the seed tray with water before filling out a label with the date and variety to help me keep track.  Then, it's indoors and onto the windowsill for germination.  With the heating on in the house, they should have ample of warmth for germination to take place, but I may also decide to switch on the heated propagator if we get particularly cold weather and the house cools down too much.  Time to germination is quite varied, but will happen between 2 to 4 weeks.  I keep the lids on the trays until the first signs of germination to help retain the moisture in the trays.  It's important to keep an eye on this and give them a spray every few days, just to make sure the compost mix doesn't dry out.

Once germination has taken place, the lids can be removed from the trays.  The seedlings will soon start sending up tall grass-like leaves, so will need the additional head room!

One year, I experimented with covering the seeds with a layer of vermiculite instead of compost seed mix.  I didn't see any difference in germination or growth so now I just stick to topping off the sowing with normal seed compost mix.

Occasionally, when things start to get busy on the windowsill and I need to make room, I'll move the onion seedlings under artificial lights.  Artificial lights will never be a total substitute for natural light (at least, not when working on a budget anyway), but you can give the seedlings more hours of light that what they would get during the Winter months.  

As the onion seeds germinate and grow, you may notice that the husk of the seed sticks to the tip of the onion leaves.  They can be removed but you need to be very gentle to do it to avoid snapping the leaves.  At this stage, it's now just a case of leaving the seedlings continue to grow and develop.  Each seed will send up a second leaf to join the first one.  When the seedlings get to this stage, and have leaves around 4 or 5 inches long, I then take them onto the next stage.

Some people will leave the seedlings in their trays for much longer, and will then transplant them directly into the ground.  I prefer to pot them on and give them more time to develop, so now I do two things.  Firstly, each of the seedlings are picked out of the seed trays, and I pot them on into trays of root trainers containing my potting mix.  Also at this point, I move them into the polytunnel.  The change in compost gives the growing seedlings a nutrient boost and the light in the polytunnel means they have everything they need to continue putting on some strong growth.  The seedlings still look quite week and feeble at this point, and potting them on takes a very steady hand.  Getting to this stage generally takes place 8 to 10 weeks after sowing.

Now the seedlings have their own cells, they can be left to grow on.  In extreme frosts, I may put some fleece over the plants even though they are in the polytunnel, or put them within a smaller grow house inside the polytunnel.  The plants themselves are pretty tolerant of the cold, but the risk could be the compost freezing solid and damaging the roots.  Of course, you always have the option of bringing them back indoors for a few days until the freezing temperatures pass.

After another 4 to 6 weeks, the seedlings should have put on plenty of growth.  It's important to keep the compost damp, but not soaking.  Often, the best way to do this is by bottom watering and letting the compost soak up moisture as it needs to.  Eventually, the seedlings will get quite long and start to thicken up.  Now is the time to start considering when the best time will be to get them outside, and into their final growing bed.  This probably will be around mid March, but beware - we've often had snow in March, so it's really important to keep an eye on the weather.  Timing can be critical.

Once confident the weather is on side, and the likelihood of any adverse weather has passed, they can be planted out into their bed where they will stay.  At this stage, the plants will continue to produce more and more green growth.  The more green growth they can put on, the better the onion bulb will be.  To aid them, I'll often add chicken manure pellets to give them more nitrogen and then continue to give weekly or fortnightly liquid seaweed feeds through the growing year.

Onions need regular watering, even daily during the driest of Summers.  Without it, the bulbs won't develop fully and potentially you may see some bolting, but as long as you keep on top of the watering, all should be good.  Towards the end of the growing period, the leaf tips of the plants will start to brown off.  We're now at the next critical stage - knowing when to harvest.  Many growers will purposefully bend over the stems of the onions when they get to this stage.  This is thought to encourage the bulb to stop growing and the leaves to die off.

I prefer to leave the plants a little longer, until the stems are quite week and almost fall over of their own accord.  Sometimes this can happen before any yellowness appears in the leaves.  But this does come with a little risk.  If you leave them too long, the onion bulbs themselves will start to split and ruin the crop.  Sometimes, it's worth harvesting a little early to avoid a spoiled crop.  Leaving them any longer won't pay any extra dividends.  I choose a dry day to harvest my onions, and once they're out of the ground, I clean them up of any soil and get them straight on the drying racks in the polytunnel.

Once out of the ground, the green growth dies back and the onions will cure.  I tend to leave them drying for at least 2 weeks, if not more.  Leaving them longer won't cause them any harm.  Finally, when the leaves have fully died back, it's time to prepare them for storage.  At this point, I'll cut the leaves off about 2 or 3 inches above the bulb.  If there is any sign of rot or the onions not being quite dry enough, I'll dispose of the affected onion, or leave it on the rack to dry out further.  I'll also give the roots a trim.

I store the onions in onion sacks in the garage ready for use whenever we need them.  The only additional work that's needed is occasional checks every week or two to make sure there are no onions going bad in the batch.  If there are, they need removing straight away to stop it from spreading.  Else, we're all good for onions right through the Winter, possibly well into Spring!