i planted 4 last year and they've not grown 1 centimetre! They've only started producing new leaves. Should I prune them? Someone said to cut them in half and they will grow really quickly?
There is no need to stake them. Yes, you can prune them down a bit to encourage more side shoots. But as mentioned from others, be patient. Sometimes, they take a while to settle, but once they do, they will grow fast.
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