Olives require deep but infrequent irrigations

Q: I am attaching photos of an olive tree. There are four trees that were planted at least 40 years ago 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. Two of the trees are OK. Two 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 advice for care?

A: Thanks for the pictures; they will be posted on my blog.

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 10 minutes on a traditional bubbler irrigation system, then this could be between 10 and 20 gallons per day depending on whether these bubblers are 1 or 2 gallon per minute bubblers.

If this is drip irrigation, it could be anywhere from a liter of water to a couple of gallons depending on the type of emitter, how many there are and how fast they release water. Let's just assume that they are not getting enough water.

Olives are traditionally grown in Mediterranean climates with 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; it means the water should be applied in a large enough quantity so it goes to a depth of about 2 feet in the soil surrounding the roots.

If the water is not a good quality water, such water containing significant levels of salt, then it must be watered even more deeply to keep salts flushed from the roots.

Infrequently means how often the water is applied. In your case, the trees are watered too often but most likely do not get enough water at each irrigation. So increase the volume of water applied and have the water come on less often.

Now, let's consider 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 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 , 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 . So the raceme dried up giving you the "mossy growth" you are referring to. But this is just an educated guess.

Q: Last year I read in your blog how to prune Texas rangers. Now I can't find that article. Can you repeat it?

A: Maybe this is it. I edited it since it included other plants. The basic rule of thumb is that plants that are not appreciated for their spring flowers should be pruned back during the winter months after leaf drop. However, if it is very light pruning, then you can do that any time.

Those plants that are grown for their flowers (this is the case with Texas rangers) should be pruned as soon as their bloom time is over regardless of the time of year. If plants bloom in the spring, then prune them as soon as they are done blooming in the spring. This will give them time to initiate flower buds during the late summer for next spring's bloom.

If they bloom in the summer months, then they put flowers on new growth during the spring. If you prune these types of plants in the late winter or early spring, you run the chance of pruning off all the flowers if they are not pruned correctly. This is very often done to oleanders when they are hedge sheared during the spring or early summer .

So with this in mind, removing wood from Texas rangers now also removes flowers so do not prune them with a hedge shears or you will remove the spring flowers as well. If you prune now, make your cuts deep inside the canopy, removing a few larger stems at a crotch, thus opening the canopy. Remove an entire stem when you do. Don't leave stubs.

Do not cut stems partway back. Leave spring-flowering growth on the remaining stems to bloom for you. By opening the canopy for light, you will see new sprouts being produced deeper inside the canopy close to your cuts. These newer sprouts will produce wood for flowers later over the next couple of years if you do not cut off the growing tips.

Next year, remove more of the older wood from deep inside the canopy and repeat this each year "renewing" older wood and reinvigorating flowering. I hope this helps .

Bob Morris is a horticulture expert living in Las Vegas; he is on special assignment in the Balkh Province, Afghanistan, for the University of California, Davis. Visit his blog at xtremehorticulture.blogspot.com.