Advice Plot #59

Thinning and Trimming Leek Seedlings

I’ve been growing leeks using the same method for the past three or four years now and it seems to be working quite nicely.

Rather than tray-sowing and then pricking out individual leeks into modules, I use deep plastic troughs – the sort of thing you can find in most large supermarkets at this time of year or online of course – about half filled with general purpose compost. On top of that I layer about 5cm of seed compost, and sow the leek seed thinly on top, before covering lightly with seed compost and watering with a fine-rose can.

A few weeks later, the leek seedlings should be about 15-20cm tall and looking rather grass-like. This is when I like to thin them out and give them a trim.

May 2017 leeks for trimming
Long and leggy leeks need cutting down to size


If there are two or more seedlings growing within about 1cm of each other, then one or more of them has to be plucked out. Be ruthless. Better to have one good seedling with enough room to grow to planting-out stage than two or three that eventually compete each other to the point of uselessness. Plus, the leek-trimmings can be used like chives, in pasta, fritatta or anything else you fancy.


Next, take a pair of sharp scissors and give your leeks a hair-cut. I gather up a small bunch and then chop the lot off at around 10-12cm in length. Trimming the main growing shoot(s) helps to prevent them becoming hopelessly leggy and tangled. It also encourages the growth of new leaves from the basal plate at the bottom of the leek, and that’s what you want: a thickening of each seedling to roughly ‘pencil thickness’, ready for planting out in June or early July.

If you’re thorough (and brave) enough then you might only have to thin your leek seedlings once before planting out, although a second trim may be needed in another three or four weeks.

How about you? Is this how you grow leeks, or do you use a different method? Let me know via the comments.

25 replies on “Thinning and Trimming Leek Seedlings”

I don’t trim or thin my leek seedlings. Admittedly they’re never pencil thick when planted out in the garden, but I also start them very late as well usually mid-March. It’s just easier for me to keep them alive when they’re in my direct care for a shorter period of time while in containers . We can have terribly hot springs once it hits, and it can take watering twice a day just to keep seedlings alive in their containers.

I know Michelle from Seed to Table starts leeks in a nursery bed out in the garden. And since her winters are very mild she starts them very early indeed and they are massive when they get planted to their permanent location, like the size of leeks I might harvest early. Although, she doesn’t grow leeks anymore due to a local rust problem.

Hi Phuong – those hot spring conditions do sounds challenging. We’ve had a couple of unseasonably hot spells this spring and our greenhouse has been absolutely roasting, so lots of watering required. The nursery bed method is one I saw on a TV programme once – I think they were growing for the veg gardens at Kew – but I’m usually not quite organised enough for that sort of thing so early in the year 🙂

I admit to lacking the courage to thin leeks. So I sow the seeds in a pot at home and then, once they are well established, take them to the allotment plot and top and tail them: Tip out the whole pot and extricate the leek plants, discarding any real weaklings. Then I take a bunch of about a dozen in hand I collectively remove any roots longer that an inch with a knife. I also remove the top third of the top growth before popping each individual into a dibbed hole and then (the fun bit) puddle them in. Last year the results were a bit disappointing, but then again everyone in the UK seemed to find last year a disappointing year for leeks.

Hi Mal – That’s pretty much how I do it as well, I just like to get them to as robust a size as I can before I plant them out – topping and tailing, as you say – hence the thinning. Our leeks went in very late last year for one reason or another, so it’s tricky to compare. But find the smaller ones I’ve been harvesting are packed full of flavour, so I’ve no complaints on that score.

Question: I live in FL. I would like to cut back my leek stems for dehydrating. They are about 8 – 12 inches high but not thick. Will they regenerate? Is this unadvisable?

Hi Connie – Assuming US ‘leeks’ are the same as UK ‘leeks’ (Allium porrum) then yes, they should re-grow, as long as you leave the base-plate – the base of the stem from which the roots emerge – un-damaged.

I’ve had leeks re-grow from sections that have been left behind when I’ve tried to pull them out and snapped them off near the base instead. It might take a full season for them to reach a decent size again, and there’s always a risk of the base-plate rotting away or drying out, but it’s worth a try.

I’ve never heard of de-hydrating leeks though. I suppose it’s much like drying onions for use as a cooking ingredient?

Hi Terry –

Ah, I’m afraid it sounds like your leeks have ‘bolted’. This means they’ve started to produce flowers in an effort to set seed. Did you plant them last year by any chance? Or has it been very dry in your neck of the woods? They usually bolt in their second year, but can bolt early if they do get too dry. It’s a survival mechanism to cope with adverse conditions.

You can try trimming the tops, but usually a leek will produce a woody stem right up the centre of the shaft to support the weight of the flower. This can be quite tough and will sometimes make the leeks rather unpleasant to eat. Your best bet might be to lift one or two and slice through them to see what the centre is like. If they’re not too tough then the rest might be just about edible as well.

Or, you could always just leave them to go to flower. They produce huge, white alium heads, which are pretty spectacular, and the bees absolutely love them. Plus you could then collect the seed to re-sow later in the season (although if you’re growing an F1 variety they probably won’t come true-to-type) which could be a some compensation for a lost crop this year?

I live in Niagara Region. What has eaten all of my young leek transplants in my garden? They are eaten right off. I thought rabbits didn’t like leeks? I also have squirrels and possibly other creatures about. Or is there an insect I should blame? Maybe this unsolicited trimming will help my leeks? So discouraging!

Hi Karen – Sorry to hear about your leek woes! Do you have many problems with snails or slugs in your part of the world? They’ve been known to take the tops off leek seedlings if they’re planted out quite small. It’s when the leeks are larger and more robust that they cope better with that sort of attack. Or could a deer have gained access? Or another small mammal? I’m not familiar with the fauna of the Niagara area, but I’m sure there could be all sorts of culprits who would be happy to munch on a tasty leek. The leeks might grow back from the base, but it could take them a while to get going again.

I would guess cutworms.
We live in rural BC and have been battling them the last couple of years.
They like young seedlings.

Once seedlings are 3 or 4 inches tall with a good supply of true leaves, I pinch them back. You can use scissors or pruning shears, but thumb and forefinger work just fine. While your seedlings are growing indoors, toughen them up by man-handling them a bit.

Hi June – I tend to use around 10-15cm of soil/compost – leek roots are fairly shallow, but you need to allow some depth for drainage so they don’t end up waterlogged – in a trough that’s deep enough to accommodate it with a few cm at the top to allow watering without run-off.

I just started my first raised bed garden and am clueless! I bought some leek seedlings from a nursery. They look like little chive clumps so I almost thought maybe someone confused the labeling . We already planted them in the raised bed but it’s only been two days. We followed the directions on the little tags about spacing between the clumps. I was looking at a picture we took, and, trying to picture how big leeks get, realized it looked off. This led me to look up how to plant leeks and didn’t realize I needed to thin them. Since I didn’t grow them from seed, I’m wondering if I should thin them now and replant, spaced out, or keep them as a clump and wait until they are pencil sized (so I guess resembling green onions/scallions) and then do it? Or do it both times? Any advice is appreciated.

Hi Justine – Don’t worry, you’ll get the hang of things! Keep reading around the subject, try a few things, see what works.

As far as your leeks, I’d say leaving them until they’re about pencil-sized and then lifting, splitting and re-planting them is a good idea, yes. You’ll run less risk of damaging them that way, although if the clumps get too crowded you might need to do them sooner than pencil-sized.

Fingers crossed you’ll be enjoying lots of lovely leeks next winter!

Hi Darren : I’ve planted leeks last year and got pretty good results . But this year I’m doing something different . I have been watching many different video’s. So this year I used a cut off shovel handle and marked it 6” up shaft . Then I make a hole on a 6” grid each way. Then I take my leek bunch shake all the dirt out and place in water . Separating them all and untangling . Then I place one in every hole . After I’ve planted all of them I fill each hole to the top with water . Not backfilling them at all . I’ve planted them now near a month . They are doing great . End result is will have long white leek . I started them end of January and planted them near a month ago . I live in Vancouver area .

Hi Vic – Ah yes, that’s a very traditional method, tried and tested. We call it ‘dibbing’ over here in the UK 🙂

Hello! This is my first time growing anything and I’m concerned about my leeks. I planted seeds in small modules about 15cm deep with roughly 3 seeds per module, in seed compost. I have put them on a sunny windowsill, sometimes covered with the transparent plastic lid, but they are now too tall for it! They started off growing and I was so excited, but now they are growing so tall but so thin that they are starting to fall over. I am not sure if I need to thin them out, or if the soil perhaps isn’t deep enough, or if they will ever get thicker. Do you have any advice? Thank you!

Hi Connie – Sounds to me they’re starved for light. A lot of windowsill-grown seedlings struggle to get enough light so they grow fast and leggy to try to reach the source. They might do better outside, in a sunny but sheltered spot, and somewhere you can keep an eye on them to make sure they don’t dry out. They might benefit from being transferred to a deeper tray or planter rather than the modules as well – they’re only going to get so much nutrient from the compost in the modules, and once that’s exhausted they won’t grow on or thicken. Good luck!

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