Justin Roberts

I found this explanation helpful:

"What does this mean? Leaving aside the grapevine metaphor for now, we can find a horticultural insight helpful in understanding the reference to olive trees.

The olive tree (Olea europaea) is very long-lived. Two thousand year-old trees are not unknown, and some exist today. The trunks of old olive trees grow to diameters of over two meters. These trees continue to produce ample foliage and fruit, a fact that may be alluded to by the blessing in Psalm 92:15 (More about that another time—The metaphor here is almost certainly not a continuation of the simile to the date palm and cedar in the preceding verses.) The wood at the center of the aged trunk eventually disintegrates, leaving the large, hollow trees fragile and vulnerable to damage by high winds.

However, the aged olive tree has a way to ensure its own safety. It is one of a number of trees that send up new shoots from their outlying roots. These small young trees surround their “parent” tree, serving as windbreaks that help to protect the aged, hollow tree in the center.

In this case, the central parent tree has died, or at least is obscured by the densely intertwined boughs of its offspring that encircle it. This provides a graphic illustration of the psalmist’s vision of children who surround and support their aged, righteous parents. If we’ve done a good job as parents and as adult children, caring for our own parents when they need us, we can expect our children to follow the example that we (and the olive tree) have set for them, caring for us in our later years. It is also a reminder of our obligations to our own parents and to our Heavenly Father."

http://www.torahflora.org/2008/08/may-your-children-be-like-olive-trees/

May 17 2016 • Report