Potatoes

I have a problem with my potatoes which I have also had in other years. The seed potato is certified (Cliff kidney). The lush-looking ones I planted two weeks before the odd-looking ones. They are in different parts of the garden. I think it must be something to do with soil. I would be very happy to get some adivce on this issue.

Is it a good time to get some spuds into the garden be ready for Christmas Day?

My potato tops are 700mm high and they have only been in the ground since the middle of August. Why have they grown so tall in such a short space of time?

When is the best time to plant out potatoes in Dunedin? And what is the best method for growing them? 

When chitting potatoes, if I have a potato with a few healthy-looking shoots, can I cut that potato in half and plant both halves? Do I need to cure the skin on the cut pieces? If so how do I do this?

I was wondering if September is a good time to get some spuds into the garden to be ready for Christmas day?

When is the right time to plant potatoes? We are afraid that frosts will kill the tops. 

This year I planted the usual potatoes and about half way through the  season the leaves started to close up and had brown edges. When I dug them up the potatoes were marble size or smaller. I plant in a different place each year. Can you help?

I have trouble growing new potatoes. I’ve tried rotation, fertiliser, a variety of seed potatoes, but to no avail. When I cultivate, they are the size of small marbles. Why is this?