The French prune is self-fertile; that is, it does not require the presence of other plum species for pollination of the blossoms.  It is the Robe de Sergeant prune which is defective in pollination and which is presumably assisted by proximity to the French prune.  If you wish to grow Robe de Sergeant prunes your question of interplanting would be pertinent, but if you desire only to grow French prunes you need not plant the Robe de Sergeant at all.

Cultivating Olives.

How deep should an olive orchard be plowed?  I was told that by plowing deep I would injure my trees, in cutting up small rootlets and fibres which the olive extends through the surface soil.  Is this so or not?

Plowing olives is like plowing other trees, the purpose being to get a workable soil deep enough to stand five or six inches of summer cultivation, usually.  If you have old trees which have never been deeply plowed, you would destroy a lot of roots by deep plowing, and you should not start in and rip up all the land at once.  You can gradually deepen the plowing, sacrificing fewer roots at a time, without injuring the trees if they are otherwise well circumstanced.  Small rootlets and fibres in the surface soil do not count; they are quickly replaced, and if you do not destroy them, the whole surface soil, if moist enough, will be filled with a network of roots which will subsequently make decent working of the soil impossible.

Moving Old Olive Trees.

Would there be anything gained by transplanting old olive trees 6 to 8 inches in diameter over nursery stock?  They would have to be shipped from Santa Clara to Butte county and grafted.  Would they come into bearing any sooner and be as good trees?  Could the large limbs be used to advantage?  Would the fact that they are covered with smut cause any trouble?

Old olive trees can be successfully moved a long distance by cutting back, taking up a ball of earth, and possibly a short distance with bare roots if everything is favorable.  But do not for a moment think them worth such an outlay for labor, freight and hauling which such a movement as you mention involves.  The trees on arrival would probably only be firewood, and if they lived, the time required in getting a good growth and grafting, etc., would perhaps be as great as in bringing a young tree of the right kind to bearing, and the latter would be a better tree in every way.  Large limbs can be split and used as cuttings, but the tree would be growth on one side and decay on the other.  Use the smaller limbs for hard-wood cuttings and the balance for firewood.  The smut shows that the trees are covered with scale insects and might indicate that it is better to burn up the whole outfit unless you learn to fight them.

Darkening Pickled Olives.

Is there anything that will make olives keep their black color when put into lye?  When I put my first picking of ripe olives in lye, a large part of them turn green, the black leaving the fruit.  My formula is one pound of lye to five gallons of water.  Have you any better formula?