Insufficient chill

also called Low chill, Chilling requirement not met

A fruit tree that grows well and never fruits. It needs a set number of cold hours in winter to break dormancy, and your winter is not cold enough for long enough.

Disorder Serious Doesn't spread

What you'll see

Buds opening late, unevenly and over a long straggling period rather than all together.
Many flower buds simply failing to open at all, and dropping off dry.
A thin, scattered blossom and almost no fruit set, on a tree that is otherwise vigorous.
Leaves emerging before or instead of the flowers, in the reverse of the normal order.
A tree that grows well, looks healthy and has never given a crop in the years you have had it.

Why it happens

Deciduous fruit trees count cold. They accumulate hours between roughly 0 and 7 °C through the winter, and until they reach the number their species and cultivar requires, the buds stay chemically locked. A tree needing 800 hours in a place that gives 400 will grow perfectly well and never come out of dormancy properly. Very warm spells in midwinter can even subtract from the total.

Mild-winter regions — the deep south, coastal California, the Gulf, and increasingly places that used to be cold enough. Also caused by planting a northern cultivar in a warm zone, or by a garden in an unusually mild urban heat island.

Treating it

There is no cure for a mismatched tree. Establish whether the chill requirement of the cultivar matches your area — the numbers are published.
Replace it with a low-chill cultivar if it does not; grafting a low-chill variety onto the existing rootstock is the quicker route.
Rule out the other causes of a non-fruiting tree first: no pollination partner, too much nitrogen, too much shade, frost on the open blossom, or simply a tree too young.
Dormancy-breaking sprays exist commercially and are not practical or worthwhile in a garden.
Site the tree where it gets the coldest air the garden has — a low, open, north-facing spot rather than a sheltered south wall.

Keeping it away

Look up your area average chill hours and buy cultivars rated at or below it. This is the whole of it.
Choose low-chill peaches, apples, plums and cherries, which are widely bred and readily available.
Buy from a regional nursery rather than a national catalogue; they stock what fruits locally.
Allow a margin, since chill hours are trending downward in most places.
Plant the tree in the coolest part of the garden rather than the warmest.

Who gets it

Apples, pears, peaches, cherries, plums, apricots, blueberries and currants — the deciduous fruits.