Chickweed amongst the onions.

I assume it is your plot's annual weed of choice   

Mine is speedwell. 

I very often lay down wetted newspaper, top with HM compost and then cut small cuts into the paper and plant setts straight in.  the paper will keep the weeds down a little, but to be honest, you are always going to get annual seeds reseeding into the surface.

On the bright side, chickweed is edible. 

So are you saying that you get it infesting a different bed every year?    Never heard of intelligent weeds before. I wish my chickweed would be more selective about whereabouts in the plot it chooses to infest!