Hey Joy. Avo's are amongst the pickiest fruit trees you'll ever see. I had 2 which did what yours is doing, i planted the third one in an ex vegie bed and it is thriving. They require excellent drainage but don't like wet feet. They also like a cool soil, so heavy mulch is a good idea. High levels of humus is another preference, so plenty of organic matter in the soil is also necessary. If you want an avo to do well, spend time on the soil. Compost galore, manures, blood and bone meal and heavy mulch. Good drainage and a regular water supply. Try and plant out of the cold wind in a protected spot and keep the soil on the dry side of moist. One thing is for sure, they are worth it. The one thing i'm sure about is that your tree is not happy, probably for one of the above reasons and most likely a soil preparation thing.

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The secret is the soil.