Fruit does seem to improve with age of trees in many species. This is why it’s important not to discard a tree just because you don’t like its first year’s offerings. I would guess that in a young tree it saps a lot of reserves in the plant to produce the fruit so perhaps that is why they are not so good. As the plant gets older and has more reserves it can put more nutrients into each fruit. Another factor is over production and thinning of fruits. If a tree makes too many fruits the amount of nutrients will not be as high per fruit. Ref: Oscar – Hawaii
Trees that won’t fruit. Some trees need a dry period to initiate flowering. Ref: Oscar – Hawaii
Some Myths Worth Busting by Anne Raver ref: New York Times How does Tony Avent, the horticultural mythbuster, grow so many plants successfully in his garden? Rule No. 1: he uses the same mix of 40 percent native soil, dug on his own land, and 60 percent compost for every plant. ”The soil for every plant we have is prepared exactly the same, whether it’s a pitcher plant or an agave,” Mr. Avent said. ”Every square inch of these gardens has the same pH, between 6.2 and 6.5, which is ideal for almost every plant. The idea that this plant needs 5 and this one needs 8 is just not true.” Succulents like agaves and cacti, however, need excellent drainage, so for these, he tills a foot of PermaTill (slate that has been heated to 2,000 degrees, so that it expands and becomes porous) into mounded beds of his regular soil and compost mix. A full soil analysis, for nutrients as well as fungi-bacteria ratios, will tell you what elements are missing. ”Our gardens are on sand, so we add greensand,” he said, which is mined along the East Coast and is high in potassium. Gardeners with clay soil might have to add rock phosphate. But never add sand to lighten heavy soil, he advises. And don’t add rocks to the bottom of a pot to improve drainage: ”Water only runs through materials of similar porosity, so if you put rocks in the bottom of a pot you’re actually making the drainage worse.” Mr. Avent said he stopped using pesticides and chemical fertilizer in his outdoor gardens 20 years ago and was amazed at the improvement in his soil and plants. Conventional wisdom says that plants can’t tell the difference between a chemical fertilizer and an organic one, he noted, ”but the microbes do — the fertilizer was burning up the compost.” After he switched to organics, he said, ”it took about a year before everything started jumping. Our insect problems disappeared. It was just amazing.”
Some fruit trees have strong apical dominance and young trees can become “leggy” with poor side limb development. One can reduce the apical dominance in this case, or, in cases where limbs are broken off by accident, by cutting off the auxin flow above side buds that one wishes to stimulate. This is often done by orchardists for young trees: Select the bud along the leader (stem) where one desires a side branch to develop, or where one already is present, but growing too weakly. With a sharp knife, make a horizontal cut about a half-inch above it, just deep enough to break the cambium and only about a quarter of the way around the stem. This breaks the flow of auxins that had suppressed its growth. Later, when a bud breaks, it can be trained or pruned as needed. Occasionally, strong apical dominance is advantageous, as in the “Ballerina” apple trees. These trees are intended to be grown in small gardens and their strong apical dominance combined with a dwarfing rootstock gives a compact narrow tree with very short fruiting side branches. Ref: Wikipedia