Brown leaves on eucalyptus planted in New Zealand

Question

Previously healthy tree of 20 metres suddenly leaves turned brown and over a six week period still brown but not dropping much.

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Answer 1

Yes, wait and see how it does this spring and summer. It may be frost damage, from the characteristic partial browning on one side. If a hard freeze is sustained for a few days the Eucs can be killed; if only for a night or two, they brown like yours and then recover the next growing season.

Consider creating a drainage system for the lower property; dig a channel, install drain tiles or whatever is appropriate.

https://www.gardeningknowhow.com/ornamental/trees/eucalyptus/eucalyptus-cold-damage.htm

https://www.gardeningknowhow.com/ornamental/trees/eucalyptus/eucalyptus-tree-root-damage.htm

https://www.gardeningknowhow.com/plant-problems/environmental/tips-for-saving-cold-damaged-plants.htm