Selection is important. Kumquats Meyer and Satsuma Mandarins are the most cold hardy.”.Golden Special” grapefruitand navel Oranges and ‘Yen Ben’ lemons can survive quie hard frosts once established.Bearss Lime and “kaffir’ lime can take quite hard frosts once established.
Plant only citrus that has been budded on to trifoliate rootstock except for Meyer Lemon which will grow on own roots.
Plant large grade plants in spring once frosts are over and plant in a sunny well protected north facing site.citrus do not like cold winds.
I feed my citrus every 6 weeks.Blood & bone & sheep pellets mixed in with citrus fertiliser works well for me and a touch of potash in autumn and spring .And water though not as frequently in winter.Mulch with dark stones is good.helps keep warmth in overnight.But mulch with whatever is on hand.A sprinkle of Epsom salts is always helpful.
Protect new planting with frost cloth suspended over but not touching.This needed for at least first 3 winters.