Growth stages of avocados

Parkesy starts with ...
Hi everyone.
I've got 2 avocados planted on the mornington peninsula that haven't really done much in the first 12 months since they've been planted. Last winter the Hass dropped all its leaves after a light frost, while the bacon retained some of its leaves. They bounced back during spring with them growing their leaves back but not really any extra growth. They were plastic wrapped during the winter months, then during January and Feb I had them under shade frames only allowing in morning sun.
Drainage is excellent with the soil around here being relatively sandy. Ph is around 6.2. They've been getting fed around once a month with a good dose of powerfeed.
Should I up the feeding schedule or apply a slow release fertiliser for them? Or any other ideas as to why their growth is stunted? Or am I just being impatient!? Apart from the stunted growth they appear healthy enough.

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Markmelb says...
They look ok -- Did you give them lots of water over summer? Saturaide granules help too to wet your soil as sandy loam areas can get quite hydrophobic - not much water to even none over winter. have you used Gypsum also and zinc sulphate every 2 years.
My Lamb Hass in ground grew nearly a metre this summer - now 3mt tall.