Leeks are ‘a bundle of leaf sheaths’. Wikipedia gives this definition and I like it. Leeks are not stems or stalks, and a one-word term often used is ‘shank’.
Leeks are closely related to onion and garlic, but have a milder and sweeter flavour.
- Winter leeks with shorter stems, mostly below soil level, are hardy to deep frost and give fine harvests in early to mid-spring.
- Summer and autumn leeks have most shank above ground and risk rotting after temperatures below about -6° C/21 °F.
- Days from seed to first harvest: 150, and up to 380 for the last harvest from a sowing of winter leeks.
One sowing of, say, an early variety and a late variety, can give several transplanting opportunities at different times. Then you have a range of harvest dates over several months.
Leek seeds sownLeeks ready to harvestEarly spring, of summer and autumn varietiesLate summer through autumnMid-spring, of autumn and winter varietiesAutumn, winter and early spring
- Best climate broadly ranges from continental to temperate. Plenty of moisture is the main requirement for strong growth.
Why grow them
Leeks offer a long season of harvest and are a kitchen staple from autumn to early spring. You can use them like onions, but the flavour is more creamy and sometimes even sweeter.
- For winter harvests, leeks are especially suitable for temperate climates. They are in the garden for harvesting at any point, over several months.
Leeks are an excellent hungry gap harvest. Grow some winter varieties and leave them to grow through early spring. Some of my most valued harvests here are in the last two weeks of April, from sowings of more than a year earlier. They have doubled in size during the previous month as it warms up, and until they switch to flowering mode.
Pattern of growth
Most varieties of leek grow slowly and surely through a whole year, for as long a time as almost any vegetable.
- Sow in mid-spring. Earlier sowing is possible, for summer harvests, but keep frost off seedlings to reduce the risk of bolting.
- You can propagate seedlings, which become medium-sized plants, over a period of two to three months.
- Meanwhile, an early vegetable is coming to harvest, such as spinach, lettuce, cabbage, carrots and potatoes.
- Then transplant at any point in summer.
- Growth is rapid through autumn and continues slowly in mild winters.
- In winters below about -8° C/18° F, even leek shanks of winter varieties will benefit from some protection, such as by earthing up. Or harvest before prolonged freezing.
- Flowering is in mid-spring, according to the variety. A flower stem develops at that time (see the photo above) and is edible when young, similar to the scape of garlic.
Suitable for containers/shade?
Leeks grow really well in containers, partly because they do not need much space for leaf growth. That huge number of leeks you see in the photo below, from the one pot, did not fill any huge volume of space around the pot.
Contrast this with, say, potatoes, which need a large surface area to grow their leaves and stems compared to the container’s size.
Shade is possible for leeks, with some decrease in growth. However, do not grow them where tree roots are sucking soil moisture – in that situation, containers work better. Water containers thoroughly, every day once leeks are large.
The leeks I grew here had no feeding, then, after harvest, I emptied the pot contents onto a bed. The compost had fewer nutrients, but was still valuable organic matter.
Early varieties, sometimes called summer leeks, are King Richard, Jolant and Bulgarian Giant. They all grow long shanks above ground and can yield a lot of food. Then, as autumn turns cooler, they lose some outer sheaths to decay and risk damage when nights fall below about -4°C/25° F.
Autumn varieties are epitomised by the Autumn Mammoth types. They grow faster than winter leeks, with more shank above ground. Varieties include Autumn Mammoth 2, Hannibal, Haldor and Tornado. Plus there are hybrids such as Oarsman F1.
Winter leeks have a darker green leaf on a shorter shank, and the original Musselburgh (a village near Edinburgh, Scotland) is still available. I find it almost too short, hence low yielding, and I recommend Apollo, Toledo and Bandit.
There are also St Victor types with pretty purple flags, including Blue (Bleu de) Solaise. They flower late, in early May.
- Seeds germinate in seven to ten days. They are not rapid, often germinating at a varied rate.
Mid-spring is ideal. You can sow earlier, say at the same time as onions in late winter. However, that brings a risk of premature flowering in the summer.
- I have sown seeds in February and then lost some plants to bolting by July.
- It’s worth waiting until early April, in this climate at least. I sow a few varieties at the same time, for all seasons of harvest.
An issue with early sowing is that people who do it can make you feel that you missed the boat! This is terrible because, with leeks for example, you can sow as late as May, in the latter third of spring. You will have a lovely harvest – it will just be a little smaller, and later.
I used to sow seeds in rows in a garden bed, around the middle of April/mid-spring. Now I multisow in modules only – why the change? Partly it was from erratic germination, partly from the time and space needed; the old saying is ‘plant leeks when their stems are of pencil thickness’.
Leek transplants can actually be smaller, and, once you have the kit for propagation, it does not take long to fill a module tray and multisow leeks. Four seeds give an average of three plants per module, depending on the age and quality of seeds. In a 60 cell tray that results in 180 leeks, enough perhaps for a family in winter.
- Each leek at harvest, from a multisown clump, can weigh 100–200 g/4–7 oz, after trimming its outer green leaves. You can use the leaves as well if you wish – they are great in soups and stews.
- Results from propagation under cover are reliable and have less pest damage – see leek moth and leaf miner information below.
Push compost firmly into the trays and, before watering, use fingers to make small hollows or indents. Drop four to five seeds in each. Then level the compost, or drop a little new compost on top, and water thoroughly after sowing. Sowing depth is about 0.5 cm/0.2 in.
Four reasons to multisow
- Grow more plants in the same area of propagating space.
- Use less compost to propagate the same number of plants.
- Save time because you are planting two or more leeks for each motion when transplanting.
- Plants grow better when in clumps alongside their mates, from germination to harvest.
All in all, more from less!
You can transplant module-sown leeks in late spring or early summer, even when quite small. Or, if there are vegetables growing in the bed you want for eventual leek planting, simply keep the module-sown clumps growing – pop each one into a 7 cm/3 in pot.
Use the same multipurpose or potting compost at all stages.
Plants grow fast after potting on, and if after two weeks your ground is still not ready, pop out the contents of the 7 cm/3 in pots into a 10 cm/4 in pot with more compost. You will be repaid for the time and compost needed to do this, by a larger harvest in autumn and winter.
Your time options for transplanting leeks are considerably more wide-ranging than almost any other vegetable. They are simple to keep growing by potting on. They are not damaged if you leave them in modules for two or three weeks too long – they would just stop growing for a while, and your leeks at harvest would be smaller, but still worthwhile.
Transplant size and time
- Transplant at 10–17cm/4–7 in high, from six to fourteen weeks after sowing.
- You can also transplant leeks in late summer to early autumn, but harvests will be noticeably less.
Planting depth is much debated.
This results in a less white but still long shank, and has three advantages:
- It’s quicker and easier to set plants in the ground in shallow holes.
- Leeks are easier to harvest and with less soil disturbance, because the base of their stem is not deep in the ground.
- Plants grow better, for having their main roots immediately in contact with more soil microbes near the surface, compared to the amount 15–20 cm/6–8 in below surface level.
When plants go into 15 cm/6 in deep holes, or even deeper trenches, they will have more white at the base of their shank when you harvest. If you like that, plant deep.
When you raise leek transplants in open ground, it’s feasible to set them deeper than plants raised in modules. You may need a trowel or spade to set them deep. Harvesting will also be a spade or fork job.
- The photo below shows 100% blanching achieved by a collar of cardboard, or a pipe around the shank. In contrast, the leeks in my crate had grown from shallow planted, multisown modules, with no blanching at any stage. Peeling off an outer sheath or two reveals paler shanks.
Clumps of two to four leeks can space at 25–30 cm/10–12 in, according to how large you like them to grow.
Set individual leeks at 15 cm/6 in apart, or closer if your wish is for small leeks at harvest. From a close spacing, you can harvest every other leek, leaving the rest to grow more.
If leek moth is prevalent in your area, best cover as soon as planted with some mesh, wide enough to offer no entry point at the sides. It may or may not be on hoops.
The photo above shows an interplant that broke the rule of not having plants compete with each other. Both were needing to grow strongly at the same time. The cabbage won!
A better option would be to interplant leeks between, say, spring-sown carrots, coming to the last month of their harvest. Or transplant leeks between spring-sown lettuce, which gives the final harvest about a month later.
Leeks grow largest in moist soil. They also tolerate dry conditions, when their leaves turn darker and growth slows.
Always give water to transplants. Often they follow vegetables such as potatoes, which have sucked soil quite dry, plus there is hot sun in summer. Watering in any dry periods until mid-autumn is highly worthwhile. Give a decent amount as well.
Extra mulch to retain moisture?
Leeks are little troubled by slugs, and grow well when soil is mulched with a thin layer of straw. Hay is possible too but may have weed seeds, and possibly some weedkiller.
How to judge readiness
You can harvest small or large, at any time. If you like a decent-sized leek, allow at least three months of growth from the time you transplanted.
In early spring you need to finish harvesting before flower stems become tough. They shoot up in the middle of shanks from mid-spring, hidden inside at first, so don’t delay too long. Last harvests here are in early May, depending on variety.
How to pick
The deeper you transplanted your leeks, the deeper you need to go to dig them out.
With the planting depth I recommend for module-sown clumps, you may be able to pull out whole clumps without using any tool. Otherwise, twist and pull individual leeks or use a trowel for undercutting roots, as I show in the video.
- Before the main harvest period for leeks growing in clumps, best make a first mini-pick in early autumn of any tiny leeks, because they won’t grow large. They are the runts.
- This thinning out also reduces rust a little.
- From mid-autumn, usually, remove individual plants or clumps of leeks here and there, to thin the planting and enable more growth in remaining leeks.
When to pick and how often
Leeks store well. You could harvest, say, two clumps twice a week, for eating leeks every day through autumn. In the cool of winter, weekly harvests are good.
If your soil is about to freeze hard with cold weather arriving, harvest beforehand with some roots left on. Place leeks in a container with a little soil or compost at the bottom, somewhere with some light. They may or may not freeze and are available as needed.
Use these tables for an idea of how much harvest to expect, and how often.
No dig bed of trial – 1.5 m/5 ft wide
- Leeks Philomene, multisown on 5th April
- Transplanted on 23rd June after Casablanca potatoes
- Two rows across the bed, each with six clumps of three to four leeks
- 21 leeks per row; harvests lasted for two months
DateWeight (kg)Number of leeks3rd October0.90415th October1.32 620th October1.25 45th October1.79 926th November1.69 91st December1.9210TOTAL8.8742 leeks
Three Strip Trial, from Strip 3’s bed of 1.2 x 2 m/ 4 x 6.5 ft
- Leeks Philomene, multisown on 5th April
- Transplanted on 9th July after Charlotte potatoes
- Four rows along the bed, which is 1.2 m/4 ft wide
- Eight clumps per row, of three to four leeks in each
- Therefore 28 leeks per row and 112 leeks in a bed
- Later planting than the table above; harvests slightly later and smaller
DateWeight (kg)Number of clumps29th October2.15612th November2.14719th November2.3479th December2.09617th December2.776TOTAL11.4932 (112 leeks)
Weights are for trimmed leeks with most of the long leaf cut off. Each leek on the Two Bed Trial (first table) was on average twice the weight of those in the Three Strip Trial. The difference is from earlier transplanting and wider spacing.
The middle photo below shows a higher yield in the same Three Strip bed, three years earlier. I used the same spacing, but transplanted the leeks 18 days earlier.
Leeks keep for one to three months in winter, when harvested with roots on and stored in a container or bucket, out of the weather and cool, even freezing a little.
Or, if you trim the roots and keep leeks in, say, a cool shed below 10 °C/50 °F, they can be good for two to three weeks. Before cooking them, you need to peel a sheath or two from each leek, because they turn brown from the outside yet are still good in the middle.
Long ago, I did this from one plant, and growth from those seeds was weak, due to inbreeding from a lack of genes. Subsequently, I learnt about the need for cross-pollination, with six to ten leeks flowering together. Stems need support from early summer as they grow heavy, up to the harvest in late summer to early autumn. More details from Real Seeds.
Which pests are likely, and when
Leek moth is common in warmer areas. In the UK, for example, it’s in southern and central England, but I have not heard of it affecting Scotland.
Allium leaf miner causes worse damage, twice a year. Plus it’s harder to prevent.
White rot is a big issue if present in your soil.
Rabbits eat the stems of young leeks, potentially causing much damage. Bird netting should keep them off – make it very secure at the sides if there are more than a couple of rabbits.
Slugs and snails sometimes live and/or hide in the crevice where leaf meets shank. I have not known them to be a problem.
Leek moth (Acrolepiopsis assectella)
The caterpillars are small and mostly stay well hidden inside the newest leaves, right in the middle of affected plants.
At first there is no damage visible, but in late summer you see leaves with vertical gashes, different from the punched holes made by slugs. Growth stops and some plants may become a rotten mass of brown mush.
- Prevention is by covering new plantings with mesh throughout summer.
- Besides mesh, a possible remedy is to spray a small jet of Bacillus thuringiensis into the centre of each leek plant, every three weeks from midsummer to early autumn.
Allium leaf miner (Phytomyza gymnostoma)
Allium leaf miners are horrible pests, and are now spreading around the south and east of the UK.
- A cover of mesh from February to early June can help, and again from September to November.
These timings are to protect allium plants from the two generations of egg-laying flies, which are present mainly in early spring and again, more importantly, during mid to late autumn. However, when pupae are already in the soil, I don’t know how to protect leeks from them, except to transplant later rather than sooner, say in July, and cover with mesh throughout – also in the case of leek moth!
The white maggots look similar to leek moth and bore into and eat foliage and shanks for two weeks or so, before turning into brown pupae. Pupation occurs within stems and bulbs, in both summer and winter after the respective hatchings.
From any leaves and plants, the 3 mm/0.1 in long pupae can end up in soil. They hatch as small flies in the spring.
- I would feel safe about putting all damaged leaves and plants in the middle of a compost heap with heat of, say, 50 °C/122 °F plus.
- Rotation is worthwhile, with a gap of approximately three years.
White rot (Stromatinia cepivora) – see photos in Lesson 21 on onions
This fungus is specific to allium plants. Stromatinia exists in soil for 5–15 years, as dormant sclerotia. They spring to life in temperatures of 15–20 °C/60s °F, and when they detect allium roots nearby.
Signs of damage are leeks falling over, sometimes with bright yellow leaves, and roots covered in white mould. Best not grow any alliums in that soil for perhaps three years or more.
However, like clubroot, white rot can be prevalent where soil has been poorly looked after. Check this observation from Jayne Arnold, market grower in central England at Oxtons Organics. She wrote in an email of 20th November 2020, after their third year of practising no dig:
- ‘For the first time in 30+ years we have not had a single leek with white rot. A disease we inherited and obliged us to practice eight-year rotations, to enable us to grow alliums’.
Other possible difficulties
Leek rust (Puccinia poori) is a fungal parasite (biotroph) on leaves, but does not kill them. Therefore it’s less serious than, say, late blight on potato leaves. It makes bright orange pustules, similar to or the same as garlic rust.
Common advice is to burn or dispose of rusted leaves. At Homeacres I always put them on the compost heap, and, after eight years of doing this, I see no more rust here than when I arrived. Leeks suffered rust here in 2013, growing in ‘virgin’ soil of 20+ years pasture and no vegetables.
Rust is sometimes claimed to be a soil problem but I am not convinced. Generally, it likes moist and warm conditions – not too hot. Plants in the leek bed below, now in its sixth consecutive year of growing leeks (middle photo), suffer no more rust than they did in year one.
Allium roots leave lovely channels in the soil as they decompose, so most are good to stay there after your harvest. Like all decomposing roots, they provide food for soil organisms – just make sure not to leave any stem, which otherwise regrows little plants and flowering shoots.
Leeks finish in the winter months and any vegetable can follow, except best give a few months break before replanting any alliums.
My mini rotation in the Three Strip Trial is potatoes – leeks – potatoes – leeks and so on. We can eat potato and leek soup in winter, from the same bed in the same year. The Charlotte potatoes store until April – see Lesson 24 on potatoes.