I have a four year old orange tree which has flowered and fruited nicely in my greenhouse until this past summer, when it started losing leaves and suffering some branch dieback. There is no evidence of insects or fungus. The only difference in its care was that I had someone else watering it for me (weekly). Could overwatering explain these symptoms? Should I try cutting it back? Presently it is leafless and seemingly dea... er, dormant. Thanks in advance- Polly
Leaf loss and branch dieback are indicators of root-rot. This is usually caused by overwatering. (Once weekly is fine, so long as the tree needs water once a week. Watering can and should vary with weather conditions, soil mix, age of the tree, etc.) You might want to consider repotting the tree -- removing any rotted roots when you do -- in a soil mixture that promotes quick drainage. Prune below the dead part of the branches. Keep the tree outside in partial sun for as long as possible.
I assume that, since your orange is in a greenhouse, it is in a container.
Overwatering can damage citrus. With a good potting mix, however, that should not be a problem. See my . Citrus in a container can also suffer easily from too little water, especially during hot weather. This do-it-yourself mix keeps moisture available to roots until the mix is almost bone dry.
Don't give up hope yet. I had a dwarf lemon apparently die from frost 10 years ago. About three years later, it produced some 60 full-size lemons on a tree that is only 3' from soil to top. (I just looked out the window and saw two ripe lemons and a few that are starting to turn yellow.) This year, I thought I lost my dwarf kumquat. While my wife and I were traveling for more than three weeks, a power failure stopped our automatic sprinklers for a cycle during 100+ temperatures. Several plants around it were also dead. While we will get no kumquats this year, the little bush is now in full leaf.
Carefully check twigs and small branches. Scratch them slightly with a fingernail. If they show green, it's still alive. If there is no green, check closer to the trunk. If even the trunk shows no green, it's gone. Otherwise, just wait. If the tree is still alive, it will resprout. Repot it now, omitting all nutrients from my mix recipe except bone meal. (The other nutrients are not good for roots that are recovering from too much or too little water. Bone meal added later will not leach into the root zone.) After new growth appears, remove all sprouts below the bud union (graft point), cut away dead wood, and feed.
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