The same species behaves differently by cultivar group, so the planner resolves size, timing and support against the group rather than the species.
Standard Apple — tree, spacing in row 762 cm300 in, mature height 200–800 cm79–315 in, mature spread 200–600 cm79–236 in
Dwarf Apple — tree, spacing in row 244 cm96 in, mature height 200–300 cm79–118 in, mature spread 200–300 cm79–118 in
Which of these numbers are soft
Every number above carries a confidence tier. These are the ones the corpus does not stand behind — estimated from general knowledge, or contested between sources. They are shown because hiding them would be the dishonest half of showing the rest.
hardiness zone — estimated
how far the roots reach past the canopy — estimated
dwarf rootstock: mature height — estimated
dwarf rootstock: mature spread — estimated
ph range — estimated
dwarf rootstock: spacing in row — estimated
standard rootstock: spacing in row — estimated
Rules that apply to Apple
Well established
Hardiness zone is the correct variable for perennials, and only for perennials.
suboptimal if ignored → advise
Mechanism: Zones encode average annual minimum winter temperature, which governs whether a woody perennial survives to spring. It is the wrong quantity for an annual, which never sees winter.
THE CEILING IS A SECOND AND DIFFERENT MECHANISM, and until 2026-07-26 this rule enforced it without naming it. A zone too WARM does not kill a perennial; it fails to chill it. Deciduous fruit crops need a winter dormancy period to break bud and set fruit, so in a zone milder than a plant is adapted to it may survive and never crop. Until ISSUES #13 was decided the band was enforced at both ends; now (option E) only the cold end gates — it alone follows from the definition of the zone system — and the warm end is carried as an ADVISORY, not a refusal.
AND THE WARM END IS A CULTIVAR'S ANSWER, NOT A SPECIES', which is the honest limit of what this rule can do. Chill requirement is published per variety and varies enormously within a species, so a species-level ceiling says "the modelled range does not reach your zone", never "no plant of this kind will crop for you". So the engine offers the plant above its band and advises choosing a cultivar rated for the zone rather than refusing it — the same move invariant 3 makes for soil, applied to chill.
Evidence: confirmed against 3 sources in the research-based literature.
the 3 sources
THE FLOOR IS TRUE BY DEFINITION and needs no citation: the USDA system defines a zone AS a band of average annual minimum winter temperature, so 'a plant colder-hardy than your zone survives your winter' is the definition restated. This rule was `verified_trivially` on that basis alone until 2026-07-26. THE CEILING WAS NEVER COVERED BY IT - a minimum-temperature definition says nothing about a plant failing for want of chill - and that gap is why ISSUES #13 exists. The pointer below closes it.
OSU Extension EC 1303, 'Growing blackberries in your home garden' (Bernadine Strik), catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec1303.pdf (read 2026-07-26). THE CEILING'S MECHANISM, STATED: 'Winter cold-hardy cultivars adapted to the colder regions of Oregon (such as zones 5 to 7), may not grow normally in regions of the Willamette Valley (zone 8) where winters are warmer and plants receive less winter chill.' A plant failing in a WARMER zone for want of chill - which is what this rule's upper bound enforces and what no source said until now. THE SAME PAGE MAKES IT A CULTIVAR PROPERTY: 'Even cultivars within the same type (trailing, erect or semierect) differ in fruit quality and flavor, appearance, tolerance to pests, cold hardiness, and plant longevity', and the remedy it gives is the one this rule's rejection text now repeats: 'Minimize risk by choosing types and cultivars that are adapted to your hardiness zone.' The page then publishes a table of sixteen cultivars EACH WITH ITS OWN ZONE RANGE, which is the strongest available evidence that a species-level band is an approximation. [read]
WHAT THIS DOES NOT SETTLE. The mechanism is now named, but the corpus still carries ONE band per species where the source carries one per cultivar, and 12 of 25 perennial zones have no citation at all. So the ceiling is explained without being precise. ISSUES #13 stays open on that, and the rejection text is deliberately phrased as 'the modelled range does not reach your zone' rather than as a prediction that nothing will crop.
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.
suboptimal if ignored → advise
Mechanism: 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.
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]
remedy
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.
Apple, pear and quince share fire blight, and the tree you plant decides most of the fight: choose a resistant cultivar, hold back on nitrogen, and prune strikes out well below the damage.
suboptimal if ignored → advise
Mechanism: Erwinia amylovora infects some 75 rose family species, pear worst, and moves between trees on rain splash, on bees and other insects drawn to its ooze, and on pruning tools; soft, fast growth from heavy pruning or excess nitrogen is what it infects most easily.
Evidence: confirmed against 3 sources in the research-based literature.
the 3 sources
Clemson HGIC, 'Fire Blight of Fruit Trees', hgic.clemson.edu/factsheet/fire-blight-of-fruit-trees (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Fire blight can be very destructive to apple and pear trees. Pear trees are particularly susceptible' (crabapple and quince named as well); 'Both rainfall and insects (such as bees, ants, flies, aphids, and beetles) that are attracted to the bacterial ooze spread can spread fire blight'; 'Avoid excess nitrogen fertilization, which results in excess succulent growth, because if injured, succulent new growth is easily infected'; 'Pruning cuts of twigs and branches are made a minimum of 8 to 12 inches below any sign of infected tissue'; resistant apples 'Empire', 'Enterprise', 'Freedom', 'Gold Rush', 'Honey Crisp', 'Liberty'; pears 'Keiffer', 'LeConte', 'Moonglow', 'Orient'.
UNH Extension, 'Fire Blight' fact sheet, extension.unh.edu/resource/fire-blight-fact-sheet (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'the bacterium can infect over 75 species of trees and shrubs, fire blight is also a significant disease of landscape plants including crabapple, ornamental pear, mountain ash, cotoneaster, hawthorn, firethorn, and quince'; 'The bacteria may be spread to blossoms, twigs, and branches by splashing rain, insects, and pruning tools'; 'Make the cut at least 8-12 inches below the edge of the infected area or canker.'
UMN Extension, 'Fire blight', extension.umn.edu/plant-diseases/fire-blight (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Heavy pruning and excess nitrogen fertilization stimulate excessive succulent growth of leaves and shoots. New growth and fast growth are very susceptible to fire blight infection'; 'carefully remove infected shoots during the growing season by cutting at least 12 inches below the infection point'; resistant apples Haralson, Liberty, Red Baron, SnowSweet.
remedy
Plant a resistant cultivar where you can - apples such as Liberty, Enterprise and Freedom; pears such as Moonglow, Magness and Kieffer. Avoid excess nitrogen. Cut strikes out at least 8 to 12 inches below the damage, in dormancy where possible, and clean the tool between cuts.
A young apple or stone-fruit tree planted where an old one of its kind stood tends to sulk - stunted, uneven, sometimes dying back - because the ground an orchard tree leaves behind is not neutral for the next tree of the same kind.
suboptimal if ignored → advise
Mechanism: Apple leaves behind a soil complex of fungi and oomycetes (Rhizoctonia, Ilyonectria, Phytophthora, Pythium) together with the lesion nematode Pratylenchus penetrans; the stone fruits leave the genus-wide version, Prunus replant disease, and in peach the ring nematode with the bacterial- canker organism drives its severe named form, Peach Tree Short Life. Either way a young tree of the same kind meets that loaded soil with a root system too small to outgrow it.
Evidence: confirmed against 5 sources in the research-based literature.
the 5 sources
WSU Tree Fruit, 'Apple Replant Disease' (Hewavitharana, DuPont, Mazzola; peer-reviewed), treefruit.wsu.edu/crop-protection/disease-management/apple-replant-disease (fetched in-container 2026-09-03; read by the maintainer 2026-09-03): 'In Washington State, the disease is caused by multiple species within several genera of fungi: Rhizoctonia, Ilyonectria; oomycetes: Phytophthora, Pythium and in some sites lesion nematode Pratylenchus penetrans'; 'Many other crops can host the pathogens in this complex, thus crop rotation is not a guaranteed strategy to lower potential disease pressure. However, a five year plus rotation to a non-woody crop can help reduce pressure'; 'Choose tolerant rootstock The most important cultural control you can use is a disease tolerant rootstock'; 'Planting in old inter-row grass lanes has improved the tree growth'; 'For small-scale, soil in the planting hole can be replaced with good quality soil from a non-orchard site.'
Clemson HGIC, 'Peach Diseases', hgic.clemson.edu/factsheet/peach-diseases (fetched in-container 2026-09-03; read by the maintainer 2026-09-03): 'Do not replant old peach tree sites with new peach trees'; 'Peach Tree Short Life This is a disease caused by the ring nematode, bacterial canker organism (Pseudomonas syringae), fluctuating winter temperatures, pruning the wrong time of year, and poor horticultural practices'; 'Guardian' is more tolerant of the ring nematode (the rootstock).
NC State Extension, 'North Carolina Production Guide for Smaller Orchard Plantings', content.ces.ncsu.edu/north-carolina-production-guide-for-smaller-orchard-plantings (fetched in-container 2026-09-03; read by the maintainer 2026-09-03): 'land that has grown peaches should not be planted back to peaches for at least four to five years to avoid potential nematode problems, replant issues, and Peach Tree Short Life (PTSL) disease'; 'Rootstocks are also chosen for insect and disease resistance, such as to fire blight, and tolerance to replant disease.'
Penn State Extension, 'Orchard Site Preparation: Bio-renovation', extension.psu.edu/orchard-site-preparation-bio-renovation (fetched in-container 2026-09-03; read by the maintainer 2026-09-03): 'Take soil samples for pH fertility and nematode analysis'; 'two successive plantings of rapeseed reduce nematode populations equivalent to an application of Telone.'
Khan et al., 'Characterization of soils conducive and non-conducive to Prunus replant disease', PMC8664177, pmc.ncbi.nlm.nih.gov/articles/PMC8664177 (fetched in-container 2026-09-03; read by the maintainer 2026-09-03): 'Successive orchard plantings of almond and other Prunus species exhibit reduced growth and yield in many California soils. This phenomenon, known as Prunus replant disease (PRD), can be prevented by preplant soil fumigation or anaerobic soil disinfestation, but its etiology is poorly understood'; 'successive orchard plantings of Prunus species are subject to complex replant problems that cause serious growth and yield suppression in certain soils.' This is the genus source that extends the rule from peach to apricot, sweet and sour cherry, and plum.
remedy
On old orchard ground, don't drop a new tree of the same kind into the same spot. Have the soil tested for nematodes first; choose a replant-tolerant rootstock where one exists (a Geneva-series apple, a 'Guardian' peach); set the tree in the old grassed row-middles rather than the old tree row; or replace the soil in the planting hole. Waiting alone is not treated as a cure - many other crops host the same organisms - so a rotation is at best partial and never a guarantee.
Tree fruits differ in whether a lone tree can set a crop. Apples and most European pears are self-unfruitful: one cultivar alone will not set a normal crop, so plant at least two different cultivars whose bloom periods overlap - for apple, a flowering crabapple in bloom at the same time also works. European plums are partially to entirely self-fruitful, and a second European plum cultivar makes fruit set reliable - Japanese and hybrid plums will not cross-pollinate them. Peaches and sour cherries are self-fruitful and may be planted alone. Partner trees must stand near each other: the published distances are within 50 to 100 feet, and 300 feet at most.
suboptimal if ignored → advise
Mechanism: A self-unfruitful tree will not set a normal crop from its own pollen or the pollen of another tree of the same cultivar; it needs pollen from a genetically different, compatible cultivar, carried by bees while both trees are in bloom. That is why the partner must be a different cultivar, must bloom at the same time, and must stand within a bee's working range - and why a self-fruitful species like peach or sour cherry, whose own pollen sets fruit, bears alone.
Evidence: confirmed against 3 sources in the research-based literature.
the 3 sources
Univ. of Illinois Extension, 'Fruitfulness and Pollination' (Fruit Trees for Home Gardens), extension.illinois.edu/fruit-trees/fruitfulness-and-pollination (read 2026-08-22): 'Self-fruitful trees may be planted alone or in solid blocks of one variety. Most peach, nectarine, and sour cherry varieties are self-fruitful'; 'A self-unfruitful tree will not set a normal crop of fruits when pollinated by its own pollen or by pollen of another tree of the same variety'; 'Self-unfruitful trees require pollination by pollen from a tree of a different variety'; 'A tree of a self un- fruitful variety should have a pollinator tree planted within 300 feet'; 'European-type plums will not cross pollinate most Japanese type plums'; 'Honey bees are the most important means of transferring pollen between blossoms.'
Iowa State Univ. Extension, 'Pollination Requirements for Tree and Small Fruits', yardandgarden.extension.iastate.edu/how-to/pollination-requirements-tree-and-small-fruits (read 2026-08-22): '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'; 'Apples are considered self-unfruitful. Most apple varieties will set a small crop with their own pollen. For maximum production, however, plant at least two different varieties with overlapping bloom periods to ensure cross-pollination and fruit set'; 'Most flowering crabapples will pollinate nearby apple trees if they bloom at the same time'; 'Most European pears are self-unfruitful. Plant at least two different cultivars for maximum fruit production'; 'European plums are partially to entirely self-fruitful'; 'European plums will not pollinate hybrid plums and vice versa'; 'Tart (also called sour or pie) cherries are self-fruitful'; 'Most peach cultivars are self-fruitful.'
Penn State Extension, 'Pollination Requirements for Various Fruits and Nuts', extension.psu.edu/pollination-requirements-for-various-fruits-and-nuts (read 2026-08-22): 'Apple: Cross-pollination is always needed to produce adequate fruit crop'; 'Pear: A few varieties are self-fruitful, but a pollinizer will improve the crop'; 'Plum: A wide diversity occurs in the plums. About half of the varieties are self-fruitful and half are not. To be on the safe side, pollinizers should be provided'; 'Red tart: The commercial varieties are self-fruitful'; 'Peach: All commercial varieties, except J. H. Hale, are self-fruitful.'
remedy
Check the pollination requirement before buying. For apple and pear, plant two different cultivars with overlapping bloom - early- and late-blooming cultivars may miss each other, and for apple a flowering crabapple that blooms at the same time also serves. For European plum, pair with a second European plum cultivar, not a Japanese or hybrid plum. Site partner trees close together - within 50 to 100 feet where you can, within 300 feet at most. A peach or sour cherry needs no partner.
Another 108 rules in the corpus apply by situation rather than by species — rotation intervals, frost windows, sun, spacing and soil. Read the full evidence page.
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.
