A self-incompatible pome fruit's pollen partner has to bloom at the same time and make viable pollen - a triploid apple cannot be the pollen source, and a second tree of the same variety is not a second cultivar.
Well established · suboptimal if ignored → advise
How it works
Cross-pollination only works while both cultivars' flowers are open together, so their bloom periods must overlap - early with mid, or mid with late; early and late can miss each other entirely. A normal cultivar makes viable pollen; a triploid apple, with three sets of chromosomes instead of two, makes little or none and cannot fertilise a partner even though it needs one itself. And two plants of a single variety - including a coloured sport of it - are genetically identical, so they reject each other's pollen exactly as a lone tree does.
What to do about it
Pick the second cultivar so its bloom overlaps the first, and do not rely on a triploid apple (Gravenstein, Winesap, Mutsu or Crispin, Jonagold) for pollen - grow one only beside two other cultivars that pollinate each other. An ornamental crabapple that blooms at the same time will pollinate any apple. Two strains of one variety do not count as two cultivars. The partner does not have to share the bed: within 50 to 100 feet is close enough for the bees, so a neighbour's tree of a different variety counts - and for apple, a crabapple in bloom at the same time does too.
How much it matters: Categorical for the failures it names - a partner that blooms out of sync, is a triploid, or is the same cultivar sets little or no fruit even with two trees in the ground; it is not a dose. Like the self-incompatibility rule it states the requirement rather than checking that the chosen cultivars meet it, because the corpus does not model which cultivar was planted.
The evidence
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
USU Extension, Production Horticulture, Small Acreage / Fruit FAQ, extension.usu.edu/productionhort/small-acreage/fruit/faq (fetched in-container 2026-09-01; READ BY THE MAINTAINER 2026-09-01): 'If one cultivar is to provide pollen for another, their period of bloom should overlap, particularly early bloom.'; 'Triploid apples such as Gravenstein, Winesap, Mutsu and Jonagold do not produce viable pollen, and cannot be used as a pollinizer.'; 'Some cultivars have multiple strains such as Cortland and Redcort, or McIntosh and Redmax. Since these apples are almost identical genetically, they will not pollinate each other.'; 'Ornamental crabapples and pears are also viable pollen sources.' [read]
Iowa State Extension, 'Pollination Requirements for Tree and Small Fruits', yardandgarden.extension.iastate.edu/how-to/pollination-requirements-tree-and-small-fruits (fetched 2026-09-01; READ BY THE MAINTAINER 2026-09-01): apple - 'plant at least two different varieties with overlapping bloom periods to ensure cross-pollination and fruit set'; pear - 'Most European pears are self-unfruitful. Plant at least two different cultivars.'; the distance - 'Fruit trees that require two different varieties for pollination should be planted within 50 to 100 feet of one another to ensure a good fruit set.'; and 'Most flowering crabapples will pollinate nearby apple trees if they bloom at the same time.' Corroborated by Penn State's 'Pollination Requirements for Various Fruits and Nuts' (another rule here's verified source), whose pollinizer criterion is to 'Have a bloom period that overlaps that of the variety to be pollinated.' [read]
Where this rule stops
Apple and pear only, scoped by applies_to.species the way the toxicity advisories are. It refines the self-incompatibility rule for the pome fruits rather than widening it: that rule says a self-incompatible crop needs a second cultivar, and this says which second cultivars actually work - bloom overlap and viable pollen. It reads no species field and states a requirement it cannot verify, because the corpus models no per-cultivar bloom period or ploidy; adding that data would sit inert without a cultivar picker to consume it, so the honest home is the advice, not a table. Kept separate from the self-incompatibility rule so each states one mechanism.
Plants this fires on
Change history
Every change to this rule is one commit. This is what the project's version history records — the date and the reason — not a summary of it.
- corpus: promote another rule here to verified, Promising -> A (maintainer read)
- corpus: add another rule here — pome-fruit pollenizer compatibility (O128 T1)
Cite this page
Milpa Gardens. "A self-incompatible pome fruit's pollen partner has to bloom at the same time and make viable pollen - a triploid apple cannot be the pollen source, and a second tree of the same variety is not a second cultivar." Evidence grade: Well established. https://milpa.garden/rules/self-incompatible-pome-fruit-s-pollen-partner/
A garden-planning corpus: every claim states its evidence grade and links its sources on the page. Cite it with the grade, and add the date you read it.