There are a variety of possible reasons why your Fuji apple tree is failing to bear fruit, including pruning techniques, variety and pollination.
If the tree has never bloomed, you may be pruning too severely. Most fruit trees require the development of spurs or short shoots on which flowers will form. It is important not to cut off all of the 1-year-old growth.
Allow dappled light to enter throughout the tree by thinning out crowded growth. Lack of sunlight can also prevent flowering and fruit set. In addition, avoid excessive heading cuts, especially during the dormant season, since heading encourages vigorous growth and reduces flower development.
If the tree has bloomed but has never set fruit, it may not be a Fuji or may need to have an additional pollinizer placed nearby to encourage bees and pollination. Although the Fuji cultivar should be "self-fruitful," meaning that it should not require cross-pollination from another apple cultivar to set fruit, it may be possible that the tree just needs additional help. Because it did have one instance of bearing fruit, perhaps a nearby apple cultivar in a neighbor’s yard helped with cross-pollination.
If the tree is not a Fuji or "self-fruitful," it will require a pollinizer (a tree or branch of a different apple variety with a similar bloom period) planted nearby (no further than 35 to 50 feet away). If there is no room to plant an additional tree, a pollinizer variety could be grafted onto the existing tree.
To test this solution, try placing flowering branches of a different pollinizer variety in a jar filled with water and set the jar in the tree canopy. Bees will visit these flowers and cross pollinate the existing tree.
When choosing a cultivar for cross-pollination, be sure that the bloom times overlap with the existing tree.
If the tree has bloomed and set fruit normally but the fruit dropped off prematurely, a variety of other factors could be causing poor fruit set, including the weather. During bloom time, strong winds and cold temperatures can greatly reduce or prevent adequate bee activity. Frost during or shortly after blooming can cause young fruitlets to abort even though no frost damage is seen.
Too much or too little water during the summer can cause fruit to drop. Drooping or yellowing leaves would indicate improper irrigation.
In addition, backyard fruit trees do not require heavy applications of fertilizer. Too much nitrogen will cause excessive new growth, which will shade out branches and cause poorer fruit set.
Depending on where the tree is located, it may be receiving too much shade from nearby trees or buildings or is competing for nutrients from other plants. Root constriction caused by hardpan or compacted soil, sunburn, borer insects, soil nematodes, root rot, powdery mildew and spider mites might also be affecting the tree. Take a close look and see if you can observe any other factors that might be impacting the tree’s health.
