The Bay Gardener by Dr. Frank Gouin

Dreaming of Fruit Trees?

Then you need to know about cross-pollination

When you get to the tree section of the seed catalogs that keep gardeners dreaming this time of year, remember the experience of the Bay Weekly reader whose Asian pear trees did not produce fruit.

He has three trees, planted in full sun 15 or 20 feet apart. All had been in the ground at least five years and flowered every spring. But no fruit followed. Following the advice of his garden center, he’d purchased all of the same cultivar.

That, I told him, was where he’d gone wrong. What the garden center did not tell him is that a cultivar cannot pollinate itself. So he needed at least two different cultivars. His lack of fruit also told me that there were no wild or other flowering pear trees, such as Bradford pears, growing nearby.

To promote diversity, Mother Nature designed her plants so that each tree or shrub cannot pollinate itself. For seeds to be produced, the pollen must come from a different seedling.

Then humans stepped in, cloning plants for their superior fruit, form, hardiness and so on. But two plants of the same clone do not equal two different plants; each cloned plant is genetically identical. In order for a cloned plant to produce fruit and seeds, it must be pollinated by another clone or seedling that flowers at the same time.

When apple orchards are planted, every seventh or eight tree is a pollinator that flowers at the same time as the fruiting cultivar. When bees are at work collecting nectar, they carry the pollen from flower to flower on their hind legs in balls, which they distribute on the female part of each flower.

Most fruit-producing woody plants are pollinated by insects. But not all plants are pollinated by bees. For instance, flies pollinate most hollies.

So if you want apples, buy more than one apple tree — each a different cultivar.

Exception to the rule: Some plants produce fruit without cross-pollination. Theses fruit are called parthenocarpic, meaning fruit without seeds. Banana and the Asian persimmons are both parthenocarpic. Have you even eaten a banana with seeds?

Bay Gardener Gives Lessons

Saturday noon lectures at Homestead Gardens, Davidsonville: 800-300-5631; www.homesteadgardens.com.

Jan. 23: Composting;

Jan. 30: Pruning.