Leeks traditionally follow early potatoes in rotation, which grow on for approximately 90 days, although we’ve usually harvested our 1st earlies at about 75 days, with good yields. I plant our 1st Early chitted tubers in mid-March, covered by old builders bags, until the threat of frost is over. So, while March-sown leeks have their bed already allocated, germinating leek seeds early also means working out where, in the allotment, this earlier crop is going to fit, and that means reorganising beds to accommodate them. I will be planting out the early sown seedlings in a nursery bed in early February, 5 weeks after sowing; they’ll then be transplanted into their beds for growing on between early March & mid-April (10-15 wks), depending on where I decide to put them, just as the potatoes are being planted. However, as early leeks tend to mature faster than winter-hardy varieties, I would be wise to plant the seedlings out early to ensure they can grow on as quickly as possible for harvest during late summer/early autumn.
Various gardening writers offer advice on sowing and planting schedules for Leeks; Charles Dowding is adamant that you shouldn’t sow before late March, with mid April the best time, and appears to have only one sowing/planting time, which probably reflects their place in his yearly planting cycle. Joy Larkcom, however, suggests trying several sowings, and it is her advice I’ve drawn upon in my experimenting. It really depends on how you organise your vegetable garden and how much you like leeks – we are northern and love them!
Make 3 sowings:
1) early varieties sown in late winter/early spring;
2) mid-season varieties: sow early/late spring;
3) late/overwintering varieties: can be sown in late spring.
I use the moon cycle to organise myself and aim to sow around either new or full moons in early January, early March and finish sowings in early April. Early sowings should be under cover or inside, later sowings can be in the open. Leeks can also be divided into: early leeks that mature quickly and can be harvested over summer into September, up to the first frosts as they tend not to be very cold-hardy; slower growing, late maturing varieties that will withstand low temperatures and can be harvested through to May. Size depends as much on the length of the growing season as on plant spacing, but I haven’t yet tried sowing an overwintering variety early, then late, to see what the difference might be – perhaps this year?
I don’t have enough space to sow four seeds per module, so tend to multi-sow, then transplant. Leeks and onions don’t mind being handled, but they do produce a forest of roots and if you multi-sow them, need gently teasing apart before planting out. There is a wonderful bonus from growing leeks as their fibrous root system improves the soil structure. I transplant into a nursery bed after approximately six weeks, moving them into their final position 10-15 weeks after sowing, when they are approximately 8” tall.
Spacing influences size and 9” each way in a bed should produce a reasonable yield of fairly large leeks; I’ve also been multi-planting leeks for the last few years; early and mid-season leeks do very well 2-4 seedlings in each hole, which gives a larger crop for the space, even if the plants may be smaller. I also multiplant at 9” each way, while closer spacings of approximately 6” will result in a higher yield of slim leeks. They grow outwards like onions and seem to thrive, although I tend to multi-plant the earlier varieties at closer spacings and give the overwintering varieties more space and plant them individually. In the end if I’m left with a lot of extra seedlings I double plant rather than discard – I always have enough to swap with other gardeners, though. Using a dibber or old spade handle, make holes in staggered lines, 9” apart each way, approximately 8” deep, drop in the seedlings, then puddle them in with water. If the weather is hot and the soil dry, fill all your dibbed holes with water before dropping the seedlings in and then water them in afterwards. This is a good way to plant after rejuvenating your beds with compost, and doesn’t disturb the soil structure as much as digging V-trenches for gradual earthing up, an old method. I give plants that are still cropping in early spring a feed of dilute comfrey/nettle liquid.
Leek Moth is the main pest that now attacks leeks; 15 years ago when we 1st began growing vegetables on the South Downs, we hardly saw leek moth, but it’s now endemic. Either cover with enviromesh/old closely woven curtains, or inspect and squash. I’ve seen crops recover from an attack, and tend not to use covers – I grow so many leeks that the cost of enviromesh is prohibitive and the net curtains are used over the fruit bushes. Rust is another problem, becoming more evident in hot weather, but there’s no remedy and plants are still usable, with the rust mainly on the outermost leaves. Because leeks are slow-growing, by spring I often need the ground the overwintering varieties still occupy. Simply dig up and heel in at an angle altogether in a corner of a bed – they keep very well this way (I’ll post a photo if I heel in the end of our crop, to show what I mean).
Just a note on the old practice of trimming roots and leaves before planting out your seedlings: Joy Larkcom notes that Belgian research had shown that this practice could lower yields (Larkcom, 2002: 274). I think the practice has been more about tidying up the plants when transplanting than about yields – the root system of leek seedlings can be astonishingly extensive!