Knowing whether an apple tree variety requires cross-pollination, is self-fertile, or is a triploid is an important distinction when determining what type of apple tree to plant in your backyard.
Most apple trees are self-incompatible and require pollen from another apple tree from a different cultivar with an overlapping bloom in order to be pollinated and produce fruit. This is known as cross-pollination. However, there are a few apple tree cultivars that can pollinate themselves and other apple trees, known as self-pollinating or self-fertile apple trees. As well, there is a sub-set of self-incompatible apple trees that are considered infertile or ‘sterile’, that cannot pollinate themselves, or other apple trees, called triploids.
How are apple trees pollinated?
Apple trees can be pollinated by insects or wind but are mostly pollinated by honey bees. Another reason to have many plants and trees that attract honey bees and beneficial insects on your property.
Pollination begins when a pollen grain from the stamen (the male organ of the flower) of one apple tree is deposited on the stigma (the female organ of the flower) of another apple tree.
The pollen grain germinates and grows down through a floral tube or ‘pistil’ that is connected to the ovule or unfertilized seed. Once fertilization takes place, the seed and fruit grow in size to produce an apple. Pollen germination in apples works best at temperatures in the range 60F-70F (15C-20C). You only need one or two warm days during the bloom period for pollinating insects to come out and for blossom to be successfully pollinated.
On most apple trees, the pollen grain must come from a different variety of apple tree as a way of ensuring genetic variability.
Self-Pollinating Apple Trees
Self-pollinating apple tree varieties are apple trees that can fertilize pollen grains transferred from different flowers on the same tree, as well as flowers of other apple trees – either the same variety or different. Keep in mind, however, that even self-fertile apple varieties will bear more fruit if cross-pollinated.
What Apple Trees Are Self-Pollinating?
Self-pollinating apple cultivars include…
- Anna Apple
- Beverly Hills Apple
- Fuji Apple
- Gala Apple
- Golden Delicious Apple
- Golden Dorsett Apple
- Gordon Apple
- Granny Smith Apple
- Jonathan Apple
- Red McIntosh Apple
- Red Rome Apple
- Spartan Apple
- Yellow Delicious Apple
Self-fertile apple trees are great for backyards or properties with limited space. However, self-fertile apple trees can be prone to a fruit disorder called bitter pit which makes the fruit rather unsightly. This seems to be related to the lack of seeds and / or small seeds which occurs in self-pollinated apples. Good quality apples tend to have larger and / or more numerous seeds – the result of good pollination. This is the reason why it is often best to plant at least two apple trees of different varieties, rather than relying on one self-fertile variety.
Self-Incompatible Apple Trees
Most apple trees are self-incompatible or self-sterile, which means the pollen from their own flowers will not pollinate other flowers on the same tree, or the flowers of a different tree of the same variety. They will require a different variety of apple tree planted close by to cross-pollinate it.
Triploid Apple Trees
Most apple trees are diploids, which mean they contain two sets of chromosomes – like humans. One set was inherited from the mother tree, and one was inherited from the father tree. Triploid apple trees are specific cultivars that contain an extra set, a third set, of chromosomes and cannot pollinate themselves or other apple trees because of their sterile pollen.
What Apple Trees Are Triploids?
Triploid apple tree cultivars include…
- Ashmead’s Kernel Apple
- Baldwin Apple
- Belle de Boskoop Apple
- Blenheim Orange Apple
- Bramley’s Seedling Apple
- Claygate Pearmain Apple
- Crispin Apple
- Gravenstein Apple
- Holstein Apple
- Jonagold Apple
- Mutsu Apple
- Newtown Pippin Apple
- Rhode Island Greening Apple
- Ribbston Pippin Apple
- Roxbury Russet Apple
- Shizuka Apple
- Spigold Apple
- Summer Rambo Apple
- Tompkins County King Apple
- Wealthy Apple
- Winesap Apple
- Zabergau Reinette Apple
If you plan on growing any of these cultivars, be sure to plant at least one self-fertile apple tree or one to two other diploid varieties for good cross pollination between all trees.
A self-fertile apple tree will be able to pollinate the triploid apple trees, and itself. Two diploid varieties will be able to pollinate each other, as well as the triploid variety, since the triploid variety would not be able to pollinate the two diploid varieties.
If you plant two trees, a triploid and a self-sterile apple tree, the triploid will get pollinated by the self-sterile apple tree, but the triploid is not able to pollinate the self-sterile variety, and only the triploid will bear fruit.
In order to pollinate the triploid and the self-sterile apple tree, a third self-sterile apple tree is needed to pollinate first self-sterile apple tree, and all three trees will bear fruit.
You might think their sterile pollen makes it more difficult and inconvenient to grow triploid varieties, but there are some advantages to growing them. Namely, they produce large crops with larger apples and are also fairly disease resistant by nature.
Apple Tree Spacing for Optimal Pollination
In general, if you are planting standard size or semi-dwarf apple trees try to plant them within 50 feet of a pollen compatible apple tree. Anything farther than that and your cross-pollination will be limited. 50 feet or closer is the optimal spacing to maximize pollination and fruit production on standard and semi-dwarf apple trees. For dwarf apple trees, keep the spacing to within 20 feet for optimal cross-pollination.
Keep in mind that a wild crabapple tree, or a neighbours tree can also serve as a pollenizer for your apple tree if you are limited on space. Look around at neighbouring properties and you just might find another apple tree. Another option if you are limited on space are multi-grafted apple trees.
Multi-Grafted Apple Trees
Multi-grafted apple trees, also known as ‘family’ trees, contain between 3-6 compatible apple cultivars, grafted onto a single tree or rootstock. These are a great option for small spaces while guaranteeing pollination from the different limbs and getting to enjoy many different types of apples without having to plant multiple trees.
Apple Tree Compatibility
In order for two or more apple trees to cross pollinate each other, the varieties must be compatible with one another and blossom at the same time.
Apple trees varieties are grouped according to when they flower. They can be grouped by letters or numbers, but the basis is whether they are early, mid or late-season bloomers. Most will bloom at overlapping times but if you plan on planting only two apple trees, be sure to choose either two early, mid or late season varieties (not triploids!) to ensure they bloom at the same time in order to maximize your chances of cross-pollination.
Even if some varieties bloom at the same time, and require cross-pollination, some varieties may still not be compatible with each other if there is a family relationship between the cultivars. For example, Golden Delicious apple trees are generally excellent pollinators for many apple cultivars but will not pollinate Jonagold or Crispin because the varieties are very closely related.
For a complete apple tree pollenization chart and to determine whether the apple trees you are considering planting are compatible, visit this chart from AC Nursery.
In all cases, whether you decide to plant self-incompatible or self-fertile apple trees, you will benefit with larger harvests of larger apples if your trees are cross pollinated.
When will my apple tree bloom? Apple trees will bloom in early spring between mid-April and mid-May after having met the required chill hours during winter dormancy. Read our guide to determine exactly when your apple tree will bloom.
Are apple tree blossoms edible? Yes, apple tree blossoms are edible and are high in antioxidants and minerals. They are mainly used as a garnish, tossed in salads, or used to make apple blossom tea. Read our guide on picking apple blossoms.