A feijoa tree that flowers well every spring and then produces almost nothing by autumn is one of the more common disappointments in a New Zealand garden, and it's almost never a disease or a soil problem. It's pollination, and specifically, it's the number of trees.
Most feijoa varieties are only partially self-fertile. A single tree, on its own, will usually flower and may set a light scattering of fruit, but nowhere near the 10 to 20 kilograms a mature, properly pollinated tree can produce in a season. The flowers need pollen from a genetically different feijoa variety to set fruit reliably, which means the fix for a lot of underperforming trees is simply planting a second variety nearby, not troubleshooting the one you've already got.
Variety choice matters here too. Older varieties like Mammoth and Triumph pollinate each other well and are still widely available. Unique, Apollo and Wiki Tu are common newer choices that also cross-pollinate reliably with an older-variety neighbour. What doesn't work as well is planting two trees of the exact same variety expecting them to fill the gap, since a variety's own pollen is a poor match for its own flowers.
Variety choice matters here too.
The flowers themselves are worth a closer look while this is being sorted out, because they double as a food source: the thick, sweet, waxy petals are edible, and birds, especially blackbirds and starlings, eat them enthusiastically through November and December. A bit of petal loss to birds is normal and not the cause of poor fruiting on its own, but bees are the pollinators that actually matter, so avoid spraying anything near the tree while it's in flower.
Once fruit is setting properly, the other common feijoa problem shows up at harvest: guava moth. The grub tunnels into developing fruit and is now well established from Northland down through Waikato, spreading further south most years. Fruit that drops early with a small entry hole and internal rot is a guava moth sign, not a ripeness issue, and picking up windfalls promptly is the simplest way to break its cycle in a home garden.
Feijoas don't ripen on the tree the way most fruit does, they drop when ready, which makes the whole cropping window easy to miss if nobody's checking the ground underneath through April and May. A well-pollinated tree in full drop is genuinely more fruit than most households can use fresh, which is exactly the problem a lone, unpollinated tree never gets the chance to have.
The pollination gap is invisible for years before anyone notices it, since a lightly fruiting tree still looks perfectly healthy. This site's premium check-ins are timed to a tree's actual flowering stage rather than a generic calendar reminder, precisely so a missing second variety gets flagged in spring while there's still a season ahead to plant one, not discovered again next autumn under an underwhelming tree.