The same species behaves differently by cultivar group, so the planner resolves size, timing and support against the group rather than the species.
Standard Plum — tree, mature height 300–500 cm118–197 in, mature spread 250–450 cm98–177 in
Dwarf Plum — tree, mature height 240–370 cm94–146 in, mature spread 240–370 cm94–146 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
mature spread — estimated
dwarf rootstock: mature height — estimated
dwarf rootstock: mature spread — estimated
ph range — estimated
Rules that apply to Plum
Promising
Do not establish Verticillium-susceptible perennials (raspberries, strawberries, stone fruit) in ground that recently hosted Verticillium dahliae — either nightshades, or a logged planting of a Verticillium host (strawberry, raspberry or other bramble, or stone fruit).
costly if ignored → warn
Mechanism: Verticillium dahliae persists in soil as microsclerotia and infects a wide host range spanning nightshades and rose family. There is no in-ground cure once a susceptible perennial is planted, so it can wilt and die from inoculum an earlier host left behind — and because the reservoir family may differ from the victim's, the same-family rotation intervals miss it.
Evidence: confirmed against 3 sources in the research-based literature.
the 3 sources
Penn State Extension, 'Bramble Disease - Verticillium Wilt' (Kathy Demchak), extension.psu.edu/bramble-disease-verticillium-wilt (read 2026-07-12): 'Verticillium wilt is caused by two common soilborne fungi (Verticillium dahliae and Verticillium albo-atrum) that have a wide host range'; 'To minimize disease, choose a planting site with no known history of this problem. Avoid land recently planted with tomatoes, potatoes, eggplants, peppers, strawberries, raspberries, or stone fruits'; 'There are no effective fungicides for management once the plants are in the ground'; 'The number of years required to eliminate verticillium, especially the resting spores from the soil, is unknown.'
UMass Extension, New England Small Fruit Management Guide, 'Brambles - Diseases', ag.umass.edu/fruit/ne-small-fruit-management-guide/brambles/diseases (read 2026-07-12): 'Verticillium attacks a wide range of plants, including potatoes, tomatoes, peppers, eggplant and strawberries. It overwinters in the soil and on plant debris. Do not plant [raspberries following these crops].'; 'Non-host crops such as corn or wheat can help eliminate the fungus if grown for at least 2 years before planting raspberries.'
Host range / persistence corroborated by the source already cited on another rule here: NC State Extension, 'Verticillium Wilt of Tomato and Eggplant' (read 2026-07-11): 'The pathogen can survive in the soil without a host for up to 10 years in the form of structures called microsclerotia'; 'affects more than 300 host families.'
remedy
Site the perennial on ground with no recent nightshades, or choose one that is not Verticillium-susceptible. Extension advises growing a non-host — corn or a small grain — for at least two years first, without claiming that clears the soil. Once the perennial is planted there is no in-ground cure.
Do not establish Verticillium-susceptible perennials where the season log records that a Verticillium host (strawberry, raspberry or other bramble, or stone fruit) previously grew — a reservoir the coarse prior-nightshades family signal structurally misses.
costly if ignored → warn
Mechanism: The same reservoir as the family-level rule — Verticillium dahliae persisting in soil as microsclerotia — but recognised precisely instead of coarsely. The family-level rule fires on a prior nightshades family, which is all a manual history checkbox can express; this rule fires on the logged planting's own species carrying the verticillium_host marker, so a prior rose family host (strawberry, raspberry, stone fruit) counts while a non-host rose family like apple correctly does not — precision the family signal cannot give.
Evidence: confirmed against 3 sources in the research-based literature.
the 3 sources
Penn State Extension, 'Bramble Disease - Verticillium Wilt' (Kathy Demchak), extension.psu.edu/bramble-disease-verticillium-wilt (read 2026-07-12): 'To minimize disease, choose a planting site with no known history of this problem. Avoid land recently planted with tomatoes, potatoes, eggplants, peppers, strawberries, raspberries, or stone fruits'; 'There are no effective fungicides for management once the plants are in the ground.'
UMass Extension, New England Small Fruit Management Guide, 'Brambles - Diseases', ag.umass.edu/fruit/ne-small-fruit-management-guide/brambles/diseases (read 2026-07-12): 'Verticillium attacks a wide range of plants, including potatoes, tomatoes, peppers, eggplant and strawberries.'; 'Non-host crops such as corn or wheat can help eliminate the fungus if grown for at least 2 years before planting raspberries.'
Host range / persistence corroborated by NC State Extension, 'Verticillium Wilt of Tomato and Eggplant' (read 2026-07-11): microsclerotia survive 'up to 10 years' and the pathogen 'affects more than 300 host families.'
remedy
Site the perennial where the log shows no previous Verticillium host, or choose one that is not susceptible. Extension advises growing a non-host — corn or a small grain — for at least two years first, without claiming that clears the soil. Once the perennial is planted there is no in-ground cure.
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.
Every stone fruit shares brown rot, and it overwinters on the tree: strip the mummies and prune the cankers before bud break, and keep fallen fruit picked up.
suboptimal if ignored → advise
Mechanism: Monilinia fructicola overwinters in mummified fruit left on the tree or the ground and in twig cankers; at bloom its spores blow and splash to blossoms, and infected fruit sheds spores that spread to other fruit on the same tree and to neighbouring trees, wild Prunus included.
Evidence: confirmed against 3 sources in the research-based literature.
the 3 sources
Penn State Extension, 'Stone Fruit Disease - Brown Rot', extension.psu.edu/stone-fruit-disease-brown-rot (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Brown rot is caused by the fungus Monilinia fructicola. It affects peaches, apricots, nectarines, plums, and cherries'; 'The fungus overwinters in mummies and cankers formed the previous season. The mummies persist in the trees or on the ground over winter'; 'Upon wetting, the spores are forcibly ejected into the air to be blown by the wind to blossoms'; 'Removing all rotted fruit after harvest helps to reduce the amount of fungus overwintering in orchards. In addition, remove dead or cankered wood when pruning.'
UMN Extension, 'Brown rot of stone fruit', extension.umn.edu/plant-diseases/brown-rot-stone-fruit (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Brown rot fungi overwinter in shriveled fruit, infected twigs and branches'; 'Infected fruit produce many fluffy, tan-to-gray spores that can easily spread to other fruit on the same tree and other trees'; 'Before bud break in early spring, remove all shriveled fruit that is still on the trees'; 'Cut out all branches with cankers and remove all twigs that have died from brown rot in February or March.'
Wisconsin Horticulture Extension, 'Brown Rot', hort.extension.wisc.edu/articles/brown-rot (fetched in-container 2026-09-02; read by the maintainer 2026-09-02): 'Brown rot is a destructive fungal disease of trees and shrubs in the genus Prunus, which includes peaches, plum, cherries, apricots and nectarines'; 'These fungi may be introduced into a garden via airborne spores produced on nearby wild or volunteer Prunus trees and shrubs. Insects such as sap beetles, vinegar flies and honeybees can also transport spores.'
remedy
Before bud break, remove every shriveled fruit still on the tree and cut out cankered twigs. Pick up fallen fruit through the summer, thin so fruit do not touch, and prune for air. Remove wild or volunteer Prunus nearby.
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 107 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.
