Issue: August 3, 2002

Apple Pollinator Need

Question:

I have always wondered why I have to plant a "pollinator" when I plant an apple tree. Why is this necessary?

Answer:

While many plants can self-pollinate, many cannot. The need for a pollinator variety isn't limited to just apples. Sweet cherries and some other fruit trees also require pollinators.

The need for a pollinator is due to several factors. First, some plants don't produce viable pollen; that is, the pollen they produce can't produce fruit in the same plant or in other plants. In other cases, the pollen from a variety, such as 'Red Delicious' can't pollinate other 'Red Delicious' trees, but another variety can. This is due to a factor called "self-unfruitfulness". Only the variety 'Yellow Transparent' is known to be completely self-fruitful, able to pollinate itself and other trees of the same variety. Some other apples are "partially self-fruitful", meaning that they can produce fruit without a different pollinator variety being nearby, but they do not produce economically successful crops, just a few fruit.

Self-unfruitfulness involves the inability of the pollen reproductive nuclei to move from the stigma (where the pollen is placed by bees) to the ovule where the pollen nuclei must unite with the egg nuclei to form the seed. This is a mechanism within the plant to increase the chances of cross-pollination and increase the genetic diversity within the species. Increased genetic diversity enhances the species' ability to survive changing environmental conditions or attacks by insects or diseases.

For fruit species that require a pollinator, you may need to plant a pollinator. However, if a neighbor within a half-mile or so is growing a variety which can pollinate yours, and if the bees are active, you will have good fruit set.

Daisy vs. Zinnia

Question:

What is the difference between a zinnia and a daisy? They look similar.

Answer:

From a distance, or from a quick glance, they do look a lot alike. A zinnia is an annual that lasts for a single growing season while the daisy is a perennial, living for several years.

They look alike because they are both in the sunflower family, the Asteraceae. As a result they have the same structure of inflorescence; that is, the same structure producing the cluster of flowers that look like a single flower. Asters, sunflowers, marigolds, and many other flowers also share this flower structure.

If you look closely at the center of a zinnia, daisy, or sunflower, you will notice that the center is composed of a multitude of "disk flowers" and around the outside are the "ray flowers" that have what looks like the petals.

So, the difference is that zinnias are related to daisies by being in the same family but differ by being in different genera (and species). Zinnias must be replanted each year and daisies can return for many years without replanting. Zinnias have many colors; daisies (Shasta daisies) are white. There are other "daisies" such as the painted daisies that have many colors, but that is yet another genus.

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Send gardening questions to Southwest Yard and Garden, Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu or at https://www.facebook.com/DesertBloomsNM/. Please include your county Extension Agent (aces.nmsu.edu/county) and your county of residence with your question!

For more gardening information, visit the NMSU Extension Horticulture page: desertblooms@nmsu.edu.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505-865-7340, ext. 113.