The Anna Apple Tree: Post Four: Pollination and Fertilization

The Anna Apple Tree: Post Four: Pollination and Fertilization

This is our fourth in a series of posts about the Anna apple tree.  In the first post, we covered the basics.  In the second, we looked at chill hours.  In the third, we used the Anna apple tree as a way to look at the concept of Brix.  In today’s post, we use the Anna apple tree as a way to look at the concept of pollination and fertilization.

Pollination and Fertilization of Fruit Trees: A Brief Overview

If you’ve ever bought a fruit tree, you may have noticed something on the tag that said that either the plant was self-fertile or that it needed another tree for cross pollination while listing some varieties.  This is the basic idea we are going to look at here.

When a fruit tree is self-fertile it means that it can be pollinated with pollen from the same tree or a tree of the same variety and still produce fruit.  When a tree requires cross pollination it means that although it might be able to produce fruit with pollen from the same variety of tree (although it also might not) it can produce more and better fruit if it is pollinated from pollen from a different variety.  The same idea can be true for trees that are self-fertile.  Although they can be pollinated with pollen from the same variety of tree, they too can do better with pollen from a different variety.

What are the Pros and Cons of Being Self-Fertile and the Pros and Cons of Requiring Cross Pollination?

When a tree is self-fertile it means that it can be easier for the tree to produce fruit.  It might be able to produce fruit from the same tree or a tree of the same variety.  The benefit of this is that the tree can have a greater chance of producing fruit.  All it needs is a tree like itself.  The con of this is that it reduces genetic diversity.  The trees that come from this pollen will be more similar to their parent trees than trees that come from cross pollination.  This lessened diversity can be a detriment if trees like this experience a stressor like a change in temperatures or a pest because the trees will be more similar and will have less of a chance that some number will be more resistant to the stress.

When a tree requires cross pollination, it promotes genetic diversity.  The trees that come from this cross pollination will be a combination of two different varieties and will be less similar than if they came from just one.  This means that should trees like this experience a stressor, the chances that some number will have an adaptation to better resist it will be more likely.  The downside of this is that these trees need trees of a different variety around them, and that can lessen the chances that they will be pollinated and it can reduce the overall number of trees that are reproduced.

Fertility Can be a Spectrum

Although it can be simpler to think of trees as being self-fertile or requiring cross pollination, it is more accurate to think of it as a spectrum from self-fertile, to varying degrees of partial self-fertility, to requiring cross pollination.  As referenced above, when a tree is partially self-fertile, it can still benefit from a cross pollinator.  A cross pollinator can help the tree produce fruit more consistently and can help it to produce a greater quantity of fruit.

What is the Cause of a Tree Requiring Cross Pollination?

Although there is a lot of biology that could be looked at here, the basic idea is that when a tree requires cross pollination, pollen from the same variety of tree won’t be able to fertilize it.  Although the pollen might get from one flower to another, once there it won’t be able to complete the process of fertilization.  

A way to think of this is sort of like keys in a lock.  If a tree requires cross pollination, pollen from the same variety of tree won’t fit in the lock and won’t be able to unlock things for fertilization, whereas pollen from a different variety will fit the lock and will be able to fertilize the tree.  There is a lot more to the idea than this, and this is a simplistic way to look at it, but it can get the idea across.

What Kinds of Fruit Trees Require Cross Pollination and What Kinds are Self-Fertile?

A number of different kinds of fruit trees require cross pollination.  Some examples include apricots, pears, some plums, some cherries (sweet), and apples.  These types of trees need a tree of a different variety that blooms at the same time for there to be cross pollination and fruit.

Examples of self-fertile fruit trees are most nectarines, peaches, and sour varieties of cherries.  These trees can produce fruit by being fertilized with pollen from the same variety of tree or even pollen from the same tree.

As mentioned, the idea of fertility can be thought of as a spectrum.  Some fruit trees can be pollinated by pollen from the same variety or pollen from a different variety and the degree to which it can do so one way or the other can vary depending on the variety of tree.

What Are Some Requirements for Cross-Pollinators?

When you buy a fruit tree that requires cross pollination, there will generally be some information about tree varieties that can be used for the purpose.  The cross pollinator will generally have to bloom at the same time as the tree you want to pollinate (so they will have open flowers and pollen can get from one to the other during the same period of time) and they will have to be planted close enough so that pollen can be transmitted by insects or other means.  The timing doesn’t have to be exact but can be looked at as blooming during the same time period during a season, either both early in the season, both middle in the season, or both late in the season.  The distance can vary but they should generally be less than three hundred feet apart, although some types of trees may need to be closer.   Additionally, cross pollinating trees have to be able to survive under the same conditions as the tree requiring pollination, for example being hardy in the same zone, requiring a similar number of chill hours, and being able to live under the same weather conditions.

Are There Trees That Can’t be Cross Pollinated?

Although some trees require cross pollination and some self-fertile trees can benefit from it, there are trees where cross pollination will not lead to fertilization.  For example, there are plums from Europe that can’t pollinate most plum trees from Japan.  There are also some trees that produce sterile pollen, such as Winesap apples.  The pollen from these types of trees won’t pollinate the same or other varieties.

What are Some Cross Pollinators of Anna Apple Trees?

Anna apple trees, like other apple trees, require a different variety for proper fertilization and fruit production.  Some examples of cross pollinators for Anna apple trees include Floribunda Crabapple, Ein Shemer, and Dorsett Golden.

If you liked learning about Anna apple trees and pollination and fertilization, check out our other posts on our TrueTreeTalk blog.  We have a post about the basics of the Anna apple tree, chill hours,  and Brix, as well as posts about a variety of other topics.  Follow us on Facebook to keep up with these and other posts.

*          *          *

ArborTrue is a science-based tree-service company in the greater Houston area.  We provide a range of services including tree trimming, tree pruning, tree removal, tree planting, arborist consultations, and more.  Call us today at 832-980-8733 or reach out to us online to schedule an appointment.