How to Grow Leeks

How to Grow Leeks: Growing Leeks As A Summer, Autumn or Winter Crop in UK Gardens & Allotments Is Relatively Easy. In This Article I Explain What I Learnt As A Commercial Leek Grower About Seed Sowing, Planting, Multi-seeded Blocks, Weed Control, Harvesting & Much More. 

I learnt how to grow leeks over 40 years ago. I’d taken over a market garden in Bedfordshire and had about an acre of greenhouses and poly tunnels which kept me busy in spring, summer and autumn but I needed a reliable crop I could grow outdoors and harvest in winter.

My father had grown leeks in our Devon garden and they had always cropped well but I hadn’t paid as much attention as I might have. So I now had to learn from scratch.  Fortunately I had a neighbour, Roy, who has grown leeks commercially for many years and he offered to be my guide as I started on my leek growing venture. Roy suggested I didn’t try to grow too many in the first year so I decided to grow just an acre of leeks! Based on the system I’d been taught by him that meant I’d have between 90-100,000 leeks to harvest by hand! I liked round figures and 100,000 was round enough for me!

So where to start?

Which Variety Of Leeks Should I Grow?

When I started we still experienced a lot of very cold long winters so I wanted a very frost hardy variety for winter production. I chose Musselburgh as my main leek variety. My rationale was that as it was bred in Scotland it would stand any weather that winter would throw at me further south. I also checked out various leek trials in my area. The experimental horticultural stations ran number of trials each year and Musselburgh had done well in my area.

Musselburgh is an heirloom variety and doesn’t actually hail from Scotland. Apparently it originated in France and was first grown in Scotland in the 1830s. It’s a relatively short leek that is slower growing than many more modern varieties, but, though its not grown commercially these days, I still grow it at in my garden. The reason being that it loves the way I like to grow leeks and copes very well with the No Dig system I employ.  I also find it very disease resistant and it copes well with rust etc.

I’m seriously thinking about expanding my leek growing and growing more late spring and summer leeks. The variety I’ve tied to date is a “mini” leek called Nipper. Nipper does well in multi-seeded modules and matures in ten weeks from sowing. That means I can have fresh leeks in my garden in mid May from an early March sowing. Nipper is however small and barely gets thicker than my finger … but it’s a delicious early leek. It can also be grown into early autumn and still crop reliably. Sadly I’ve not been able to locate any Nipper seed this year. If you know where I can get some, I’d love to hear.

There are ways to grow baby leeks and there’s more info if you follow this baby leeks link.

How to Grow Leeks From Seed

There are three ways to grow leeks from seed.

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You can direct drill them into their final growing positions, but I don’t do this as they are a long season crop and will take up too much space for far too long. There’s also more risk of weed competition if they are there for close on a year or even a bit longer!

On a small scale, (one acre was small scale) I sowed my seeds using a brush drill.
Brush drills have adjustable width wheels and were very useful in marking up areas for planting crops such as marrows/courgettes on a field scale. The field was criss crossed with the drill set at say, 3 foot wheel width.  This made a grid of wheel marks and a seed or plant could be placed at every cross or every second cross in the field.

2.

Growing in a seedbed with later transplanting is the preferred option for many people.  The seedbed can be outdoors, in which case I’d leave 6-8 inches between the rows for hoeing. Or you can start them off in a piece of guttering in the greenhouse. This gives a longer growing season and means more care can be given in the early stages. Once they have reach a few inches high they can be slid out of the guttering into a prepared shallow “trench”, watered in and they’ll grow away quite fast.

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Lastly you can module grow them. I multi-seed modules with leeks, 5-7 per module, the same as I do with spring onions. I then transplant into a No Dig bed that has been covered with shallow layer of grass mowings to suppress weeds and feed the soil. More on that later.

There are other ways to grow leeks, but these are the methods employed by championship/competition leek growers and I make no pretence to understand why they do it or how they do it. That’s not me being negative about prize leeks, people garden for various reasons, it’s me being ignorant of this growing method! However, let me explain what I do know.

How to Grow Leeks From Pips (Cloned Leeks)

Leek growers growing for exhibition use a different process to propagate leeks. Rather than use seed they clone plants. It’s not something I did on a commercial scale, it was too much faff, and not something I want to do when growing for the table. But essentially the process is to take a good leek, let it flower and when in flower to cut the flower off or in half. The leeks then produces bulbils at the cut.  These are clones of the plant and can be picked and rooted. Once rooted they can then be grown on to maturity.

How to Transplant Leeks

When your leeks are around pencil thickness they are ready for transplanting. They’ll have a good height of leaf about ground and a lot of root underground. Commercially I used a tractor and leek planter to transplant. Two people sat on the planter and we planted two rows at once. They set a plant into place each time a bell on the machine rang. and the bell setting dictated how far apart the leeks were planted. It was a simple machine, towed by a slow moving tractor, and meant each operator planted around one leek a second. That may sound fast but is very manageable and never feels fast.

The problem is all that leaf and root got in the way. So we trimmed the roots and leaves to remove surplus growth. How? Simple, as we pulled the plants out of the seedbed we’d take a handful of plants in once hand and use the other hand to twist the roots or leaves at the required level to “screw” the surplus growth off. It gave a jagged tear to the leaf but did no lasting harm and seemed to stimulate subsequent growth.

There’s another advantage to this method. When the plant goes in the ground it will wilt very quickly if it has too much top growth. The roots just can’t take up enough water to cope. By reducing both root and leaf the plant is able to settle in much quicker and soon “balances” its growth.

Of course when I farmed leeks commercially like this we had ploughed and cultivated the soil, added fertiliser and spent a lot of time making things just right. Today I know there’s another way and I’ll explain that next.

How I Grow Leeks On a Garden Scale 

Today I don’t dig my soil. I just keep adding compost to the surface and am a devotee of No Dig. At planting time I use a dibber to push a hole in the soil and drop a leek in each hole. I then water the plants in and leave well alone for several weeks. Once the grass mowings turn brown and start to shrivel I add more between the plants and this suppresses the weeds. At this stage the previous layer of grass is rotting down well, the worms are dragging it into the soil and as it breaks down it feeds the leeks. Hence I feed the soil and the soil feeds the leeks.

I’ll add mown grass 2-4 times during the season depending on the conditions. It works well for me as I have no digging to do and my soil is improving. Plus I get really good crops.

How To Control Weeds When Growing Leeks 

As mentioned above I get few weeds in the leek beds where I mulch with grass clippings. It totally suppresses the weeds and feeds the soil at the same time. However, if you aren’t a No Dig aficionado there are other ways to reduce the weed burden on the crop. And I say burden as weeds will compete with your crop for water, light, nutrients etc.

Firstly there are herbicides for use on commercial crops. I’m not advocating herbicide use, but to deal fully with growing leeks I feel I need to give all the information I have. Aclonifen is a pre-emergent herbicide for annual broad leafed weeds used by some growers. Pyridate is another chemical used by some growers. Often a growth promoter is also used. These will stimulate the crop and have the added advantage of promoting the weeds to take up the herbicide. Some of the chemicals I remember being mentioned when I grew leeks commercially have now been withdrawn for sale, which takes me on to my preferred commercial method of weed control.

The second way to control weeds in leeks is by hoeing. This was my preferred method when I grew commercially and is the one I advocate to amateurs today. Because my leek crops were planted using a machine they were in perfectly straight lines. That meant I could then use a machine to hoe in perfectly straight lines.

Making Use of a Bean Tractor To Hoe Leeks

I owned a Bean tractor. It’s best described as a very large hoe frame that has an engine to move it on four wheels. Imagine a metal bedstead travelling across the field on four wheels. Under it are a series of adjustable hoes that just skim the soil surface and perform an incredibly good job. Bean tractors were invented by Mr Bean (OK I know the Mr Bean jokes, but this was well before Rowan Atkinson walked into a studio). To see what a Bean tractor looked like and learn more about Bean Tractors click the link.

If hoed just as the weeds were emerging the Bean tractor did a great job. If however the weeds were a little bigger I’d use a conventional tractor with a standard tined hoe and drive up and down the rows a little faster than the sedate Bean tractor. This would move the soil a little more, and act almost like a potato ridger. The soil would be slightly ridged against the crop and this is in line with what the Victorian gardeners did when the ridged a leek crop. Ridging gives a longer blanched stem, controls weeds and conserves moisture to a limited extent.

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Harvesting Leeks

Commercially I used an under cutter bar to loosen the leeks in the soil .. they can have large root systems. Imagine a large U shaped flat metal bar or share going under a row of leeks. the under cutter would straddle the crop so that the leeks “sat” in the U as it was pulled through the soil. The result was leeks that could be pulled out of the ground by hand. As I pulled them I’d take a sharp knife and remove the remainder of the root. I’d then pull off any dead or dirty leaves and place the leek horizontally in an open ended box. The leaves would be cleanly cut where they overhung the box. This took just a moment .. you get very fast at this when it’s how you make a living!

Those leeks grown in tunnels from multisided modules were easier to harvest. They didn’t need undercutting but could be pulled from the soil by hand and prepared as above. The only difference is we harvested these in June when they were the size of my thumb. They were grown fast with plenty of irrigation and high nitrogen liquid feeds every day. So they were tall and we left far more leaf on them. Chefs loved the greenery for rich coloured green soups. Young leeks crops in June were uncommon and demanded a premium price that Michelin starred chefs were very happy to pay.

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Pests And Diseases 

I’ve always found leeks to be relatively pest and disease free. Though that’s not to say they are not troubled by pest and diseases.

I find the best defence against pests and diseases is to grow healthy crops in a healthy soil! And for me that means either No Dig or plenty of nutrition, preferably via adding organic matter. Grown in an organic rich soil the leeks are far more reliant and tolerate pests and diseases far better.

Leek Rust

This is the most common problem I see and is caused by a fungi (rust) that loves cooler wet weather. The wetter it is and the longer the wet spell lasts the worse the rust becomes. In extreme cases it can kill the plants but this is rare and the plants will often grow out of the condition when the weather improves. Few crops are completely free of rust so don’t despair if you see a bit of it.

The rust shows up as an orange coloured lesion and affects the plant cosmetically. But once the outer leaves are peeled off there is not likely to be a problem in most cases.

Don’t overcrowd your leeks. Dense planting encourages the conditions that suit rust. Commercially I was quite careful to ensure good spacing a is wanted maximum yield, today, as an amateur I tend to plant a bit too dense but then remove some plants as baby leeks once they start to grow big enough … ie before there’s a problem.

Onion White Rot on Leeks

I’m told this is common on all Alliums but I have never seen it on leeks. But a lot of people do get problems with it. It’s another fungal problem where there’s no cure. So if you’ve experienced this in your garden don’t grow alliums for a several  years so that the fungi dies out. OWR is more likely on onions in my experience, but a lot will depend on your location and soil type. Because fungi are encouraged by wet I find it is often worse on clay soils.

Sadly the fungal resting body, the sclerotinia, that persists in the soil can sit there for many years. Some research suggests as long as 18 years! The fungus attacks the roots so is unseen until the plant suddenly keels over.

Leek Moth Attacks on Leeks

Leek moth are tiny moths that wreak big havoc! The moth is only 5-6mm in length and is brown so easily missed. But its caterpillars attack leeks, shallots and onions where they tunnel into the plant material. On its on this isn’t a major problem, the real problem comes when bacterial and fungal rots then establish. The leek moth caterpillar have brown heads and a creamy white body with small legs.

There’s no cure but there are some preventative actions you can take. The main one being to cover the crop with horticultural fleece to prevent the moth reaching them.

Allium Leaf Miner

This is a fly, or rather the pupa of a fly. It can be distinguished from the leek moth as it is white rather than cream, but doesn’t have a head or legs.

20 years ago I wouldn’t have been writing about this pest. It was unknown in the UK. Again the problem is more about the rots that set in than the actual damage itself and that the best control is to use horticultural fleece a s a barrier to the adult. Of course this assumes there is no pupa overwintering where you intend to grow the leek crop.

If you’ve not had miner problems before, you can assume there’s no pupa in the soil. But remember this pest attacks leeks, shallots, garlic, chives and onions, so think back to what these crops were previously like where you want to grow leeks.

I’m not a great believer in crop rotation in normal circumstances, but if you’ve had allium leaf miner on a site it makes perfect sense to rotate crops and not grow alliums there again for a few years.

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