that tree has been pruned many times.. and rather horribly ...

i can see it at all the places.. where a branch makes an odd.. call it 30 degree bend ...

the question that needs to be answered first is... is it still in full sun ...

i THINK... part of its problem.. is that it is now in a great amount of shade.. as the surrounding trees have outgrown it.. and PERHAPS ... that is one of the reasons.. it has no leaves.. until it reaches above the house...

if that is the case.. and you trim it way down... it will struggle.. and perhaps not generate enough energy.. thru leaf growth.. to fruit properly ...

we need more info.. on sun.. location.. shade what part of the day ... etc ...

ken

Besides what ken said, is there root competition from that other tree nearby. Citrus have relatively modest root systems and can't compete with a tree nearby that has an aggressive root system.

And how often are you fertilizing? Orange trees need a lot of N to maintain their foliage. How often is it watered? Yes you can cut them back pretty hard and have them come back strong, but there are likely issues in its care that need to be solved as well.

First off, thank you for your replies.

It is in more or less constant shade during the winter season due it's location on the north side of the house but gets more sun in the summer. Some morning sun during winter half.

There are no competing trees beyond the one that can be seen in the background. On it's left there are some bushes but nothing major.

We've lived here for four years and the tree has always been very productive with lots of fruit. I've very recently taken a more active interest in gardening, so maintenance has been done by a 'mow and blow' gardener up until now. Found a four year old picture that shows the unfortunate decline. I don't know what kind of fertilization it has received, but it receives relatively regular water through sprinklers.

I'll happily take suggestions on both fertilizer and amount of water. Soil is clay. Zone is 10 California.

Forgot the picture (from four years ago). It's taken from the other side. Dramatic difference.