Staffordshire,
United Kingdom 
bought our second Dicksonia Antartica 3 months ago, (2 foot high) it had 4 fronds fully grown with one small one just started. Now after 3 months the new frond is the same size as the others but is terribly stunted--is it stress when it was growing it was moved?
1 Oct, 2014
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When you say just bought 3 months ago, does it have roots? Have you been keeping the crown moist? They come from areas with high rainfall, so needs a lot of water. In addition you can feed the crown to get lots of large fronds. Large fronds are best when it is in shade.
Lastly Slug damage can stunt it if it is none of the above.
1 Oct, 2014