I would consider re-potting.

First, since you're in zone 10, there will be more leeway in using heavy, water-retentive mixes.

That said, even in your warm zone, a more uniform soil mix will allow your trees maximum vitality.

In a container, water moves differently than in the ground.
In the ground, the earth itself acts as a giant wick (in most cases) to equalize moisture in the soil.
(The exceptions being low places or clay-soil "cauldrons" that pool moisture - the "bathtub effect").

In a container of soil made of fine particulate, the water will sit or "perch" in the lower inches of soil.
With gravel in the bottom of the pot, the small particles clog the spaces between the gravel and prevent the
moisture from draining out. In this saturated layer, roots may die off and rot, leading to serious problems with trees.

Truly, you want to build air into your soils. There are many ingredients to accomplish this.
Durable, stable, gritty, porous, sharp, uniformly sized particles are best - ingredients such
as bark, perlite, pumice, turface, small gravel, quartz, granite, et cetera, are excellent.

There are also specialty mixes made by Fafard that are gaining recognition:
Fafard Nursery Mix and Fafard #3, I believe. Special order.

Josh

Field soils are part of a large, working system. This system won't work unless all parts remain as part of the whole. In other words, if you remove a small portion of that system, and put it into the confines of a container, that portion ceases to function. Your plants may do okay for a while, but sooner or later, the fines in your field soil will begin to fill what larger pore spaces might be available. Those larger pores are essential for healthy development of plant roots as cell division requires oxygen and respiration gives off carbon dioxide. Without a very porous mix, soil gas exchange will slow down dramatically and maybe even cease.

I'm one who espouses the use of either the Fafard Nursery Mix or Fafard #3, both of which are professional quality potting medium with bark as the primary ingredient. They have very little in common with the potting mixes you'll find in the retail sections of your garden center, but many privately owned nurseries will be willing to special order you some OR have it in 'the back' because that's what they use for their containers.