Babbington leeks are different to tree onions etc.
Tree onions. aka, Egyptian onions, walking onions etc etc
There is a really good link..
http://www.motherearthnews.com/Organic-Gardening/2003-08-01/The-Other-Onions.aspxIn my hand I have a bag of fleemers Top stting onions from Heritage Harvest, the directions say..
Make a furrow 2-3 inches deep,put bonemeal in the bottomand mix with soil, Plant the individual bulbs 6-12 inches apart and cover with soil.
For potato onins.. I have a bag of Broome Longkeeper
Furrow 4 inches, bonemeal as above,3 5 inches apart.
Hope this helps the previous two questions.
I should add I have never grown them yet so therte may be folks who have personal experience with them