Dibbered leeks.

This is an oldie which everyone probably knows but its worth adding in case anyone doesn't.  You don't have to do it like this, but I do.

When transplanting seedling  leeks for the table into their final positions use a dibber. Rake area flat and dibber holes at required distance. The deeper you dibber the more white your leeks will have. Leeks don't need to be too big for table use so spacing at 150mm is ample enough..
After dibbering, drop in the leek (some people trim the roots and tops, but I don't bother.)

Once seedling leeks are in dibbered hole, fill hole with water, and that's it. leave the hole open and it will allow the leek to expand as it grows.

Simples.

I do exactly the same, but I also add a handful of compost to each hole after the baby leek (we call them leeklings   ) but before watering to give them a little boost and to be sure the roots are not going to dry out when its hot. 
My dibber is a very cheap one, but my mum's is the even cheaper broken handle of a fork!
And the next day go back and replant all the ones the blackbirds have pulled out ...

I do the same but must remember not to make the holes too deep they are a b****r v to get out in the winter!!

They are easier to lift than Parnsips Roitelet.

I’m posh I have two dibbers, one for best you might say. I was given one for Christmas a few years ago probably I’m not sure, I just know I didn’t buy it. The second is the old handle off my 5 pronged fork. That is the one I use.

Commercial dibbers are so short, I like the white of a leek.

I do the same but also put a toilet roll tube in the hole. Also for planting things like beans which I start off in 3 inch pots I use a bulb planter which is the same size so drop in easily. I have 3 dibbers 2 posh and one someone made for me.

I do it like that too. It's the first year I've actually got to the stage of having leeks big enough to plant out, and I have the handle from one of the many forks I've broken ready for it

... leave the hole open and it will allow the leek to expand as it grows.

Simples.

 
Ahem, is all expansion already finished for leeks? Mine got to non-invisible seedling size this year before planting out, but most are only about as big around as a finger. I think I might have managed a few thumbs! Mine are Lyon 2, which seem to suggest they could be harvested Sept-Dec.

I do the same but also put a toilet roll tube in the hole. Also for planting things like beans which I start off in 3 inch pots I use a bulb planter which is the same size so drop in easily. I have 3 dibbers 2 posh and one someone made for me.

I think I have dibber envy!

... leave the hole open and it will allow the leek to expand as it grows.

Simples.

 
Ahem, is all expansion already finished for leeks? Mine got to non-invisible seedling size this year before planting out, but most are only about as big around as a finger. I think I might have managed a few thumbs! Mine are Lyon 2, which seem to suggest they could be harvested Sept-Dec.

.
They will still be growing but slowing down now. As they are fairly small, they may continue to grow for longer before going to seed. You could try feeding them if you have anything suitable, a general fertilizer or nitrogen rich one would be good. Robert Milne in his book 'Organic Vegetable Growing' suggests using urine diluted 1:1 at 1 litre per sq metre.