Modern fruiting pear trees are grown from a rootstock and a grafted scion (small branch). The rootstock must be matched with the climate where it will be grown, and the scion determines the variety of pear the tree will produce. A Bartlett pear tree in Virginia probably has a different rootstock from a Bartlett pear tree in Iowa. Each will have predictable growth in its particular climate.
Pears require a period of cold dormancy to produce fruit. The length of cold dormancy varies between varieties and rootstock. Pear trees for southern planting zones might require only 25 to 40 days of temperatures 45 degrees or lower. Pear trees for northern climates where there are prolonged winter freezes may require 40 to 60 days of cold temperatures.
As spring temperatures become warmer, the second stage of growth, called bud swell, begins. In the bud-swell stage, the sap flow increases, and the buds begin to show the first signs of green at the tips as the pear tree comes out of winter dormancy. Bud swell refers to the small buds that are still only "bumps" along the branches.
Bud Burst and Green Cluster
Bud burst is the next growth stage. It happens when the bud tips break open and the tiny flower buds are exposed. They do not resemble flower buds, but instead look like small tangles of fuzzy green yarn.
The buds continue to grow until they reach the green cluster stage. Here, the buds are visible as individual flower buds on longer stems. They are still completely green.
White Bud and Bloom
As temperatures continue to warm, pear trees move into the white bud stage of growth. The buds begin to open, showing the still tightly wrapped white petals. The stems continue to lengthen.
The bloom stage occurs when the flowers are fully open, and pollination can take place. Without proper pollination, the tree will be barren.
Petal Fall and Fruit Set
Petal fall occurs after the blossoms have been open for several days. They may or may not have been pollinated. A pear tree reaches the petal fall stage when about 75 percent of its petals have fallen.
Depending on the variety, fruit set is evident seven to 10 days after petal fall. At this time, the flower ovaries that have been successfully pollinated will show the beginning swell of fruits.
Pears ripen in late summer through fall. Different varieties ripen at different times. Ripening also may be affected by weather conditions such as too much or too little rainfall, extended hot spells, or unseasonable cool weather.