very small flies on leek seedlings

They sound like algae flies - they are a real pain. The adults don't harm anyhting, but the larva eat the algae on the surface of compost and in the process also chomp on the roots of seedings. You can get sticky cards that trap and kill the adults. The larva are prone to desication, so, if you can, allow the surface of the compo to dry out - easier said than done when you're raising seedings..... good luck with it.

Leeks are grown as a winter crop, sown outside in March, transplanted from the rows in a deep dibber hole in May/June, taking most of the roots as you transplant, watered in with a weak liquid feed, earthed up slightly as they become taller will produce a good crop for eating. Sowing leeks in the greenhouse may have attracted onion fly which will contaminate anything of the onion family. If you scroll back you will find an answer on growing leeks for show.

Wouldn't have thought onions flys would be about at the moment, but if you look at my blog on teh subject you will see that Leek Moth is becoming a serious problem in some areas - that's not your little flies, but once planted out it pays to be aware of the moths...

Dr B - I always start my leeks off under cover in a trey, when they're up I slide the whole lot into a scrape on the ground, let them grow on and then lift adn transplant when they're about pencil thinkness. An old gardener told me to do it that way and it works well for me.

Sid, yes that method is great, you do not have very much root damage, we are further down in the South so are a fortnight earlier, so we sow directly into the ground outside. I agree the leek moth is very troublesome, so is mildew and smut when Leeks are grown too soft.

Leek moth reached here about 3 or 4 years ago - mine is the first case in Herefordshire recognised by the RHS - it's spreading north alarmingly fast :-( I'm going to have to net them this year.