Olive Trees With Mossy-Like Growth On the Branches

Olives with mossy growth inside

Q. I am a master gardener in Lake Havasu City, AZ. I am attaching photos of an olive tree at LH Baptist church. There are 4 trees and have been planted at least 40 years ago from what anyone can remember and they have "always" been trimmed into little balls. They are being watered for about 10 minutes every day in the summer and about 10 minutes twice a week in the winter. As you can see in the last picture, they do not have wells but have a raised brick planter box. It's hard to tell but the tree is about 1 1/2 feet deep in this planter. Two of the trees are o.k. There are many basic problems with the care; however, my main question is that 2 trees appear to have some type of mossy growth inside on the branches. It shows up best on the last picture. Can you help identify this and give any advise for care.

Olive mossy growth on the inside

A. I am going to have to do some guessing on this one. This is not something that comes to mind easily. First of all telling me that they are watered in minutes doesn’t give me any idea of how much water they are getting. If  this is ten minutes on a traditional bubbler irrigation system then this could be between 10 and 20 gallons per day depending on whether these bubblers are one or two gallon per minute bubblers. If this is drip irrigation it could be anywhere from a liter of water to a couple gallons depending on the type of emitter, how many there are and how fast they release water. Let’s just assume I guess that they are not getting enough water.

Olives are traditionally grown in Mediterranean climates; hot dry summers and cold wet winters. Olive trees are very drought tolerant but if they are being grown for their fruit then they must have adequate water during times of fruit production. Adequate water for trees is watering them deeply but infrequently. Deeply has to do with the quantity of water applied at the time of irrigation. Deeply means the water should be applied in a large enough quantity to water to a depth of about two feet deep in the soil surrounding the roots. If the water is not a good quality water, such as saline or water containing significant levels of salt, then it must be watered even more deeply to keep salts flushed from the roots.

Olive flower racemes

Infrequently means how often the water is applied. In your case, the trees are watered too often but MOST LIKELY not enough water is applied at each irrigation. So increase the volume of water applied  AND have the water come on less often.

Now the mossy growth. This is where I am taking a bit of a shot in the dark. If these olives were planted 40 years ago they were olives that produced fruit. Fruitless olives were not being marketed then. There is no mention of fruit production. Olive flowers come out on clusters called racemes which also bear the fruit. If there is inadequate water (drought stress) the tree will have a rough time keeping these flowers and racemes alive and probably produce little to no fruit. My guess is that these are dried up flower clusters (racemes) that never were sustained for producing fruit either by a lack of pollination or enough water to keep the raceme alive and so the raceme dried up giving you the “mossy growth” you are referring to. But this is just an educated guess.