The same species behaves differently by cultivar group, so the planner resolves size, timing and support against the group rather than the species.
Globe Eggplant (Standard / American) — bush, spacing in row 60 cm24 in, mature height 75–120 cm30–47 in, mature spread 60–75 cm24–30 in, days to maturity 80–100
Italian Eggplant (Oval) — bush, spacing in row 55 cm22 in, mature height 60–90 cm24–35 in, mature spread 55–60 cm22–24 in, days to maturity 70–90
Asian Eggplant (Long / Slender) — bush, spacing in row 45 cm18 in, mature height 60–90 cm24–35 in, mature spread 45–55 cm18–22 in, days to maturity 60–80
Patio Eggplant (Dwarf) — bush, spacing in row 40 cm16 in, mature height 30–60 cm12–24 in, mature spread 40–45 cm16–18 in, days to maturity 50–70
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.
ph range — estimated
sowing depth — estimated
standard: mature height — estimated
standard: mature spread — estimated
standard: days to maturity — estimated
italian: mature height — estimated
italian: mature spread — estimated
italian: days to maturity — estimated
asian: mature height — estimated
asian: mature spread — estimated
asian: days to maturity — estimated
dwarf: mature height — estimated
dwarf: mature spread — estimated
dwarf: days to maturity — estimated
Rules that apply to Eggplant
Promising
Do not plant nightshades in ground that held nightshades within 3 years.
costly if ignored → warn
Mechanism: Alternaria solani (early blight) and Septoria lycopersici overwinter on tomato debris and solanaceous weeds; a 2-3 year break plus debris removal starves this inoculum. Fusarium has a very narrow host range, so rotating away from the host is effective. Verticillium is the exception: microsclerotia persist ~10 years and it infects 300+ host families, so a garden-scale rotation does not control it.
Evidence: confirmed against 5 sources in the research-based literature.
the 5 sources
Clemson HGIC, 'Tomato Diseases & Disorders', hgic.clemson.edu/factsheet/tomato-diseases-disorders (read 2026-07-11): 'tomatoes and related vegetables, such as potatoes, peppers, and eggplants, should not be planted on the same land more than once in three years.'
NC State Extension, 'Septoria Leaf Spot of Tomato', content.ces.ncsu.edu/septoria-leaf-spot-of-tomato (read 2026-07-11): 'The fungus is known to overwinter on infected tomato debris and solanaceous weed hosts'; 'Rotate away from tomato for 2 or more years.'
NC State Extension, 'Verticillium Wilt of Tomato and Eggplant', content.ces.ncsu.edu/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.'
Plant nightshades in different ground, or wait until 3 years have passed since this ground last held them. Clear and remove the old debris either way — the inoculum overwinters on it.
Do not plant a juglone-sensitive species within the root zone of Juglans. The sensitive list is the hazard's own, and it is wider than the nightshades - it also carries apple and cabbage.
fatal if ignored → block
Mechanism: Juglans roots exude hydrojuglone, oxidized to juglone, a respiration inhibitor. nightshades are highly sensitive: wilt and death.
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
UW-Madison / Wisconsin Horticulture (Joy, Hudelson & Jull, rev. 2024-02-28), 'Black Walnut Toxicity', hort.extension.wisc.edu/articles/black-walnut-toxicity (read 2026-07-13): 'Vegetables such as tomato, potato, eggplant and pepper ... are particularly sensitive to juglone'; 'The toxic effects of a mature black walnut tree can extend 50 to 80 feet from the trunk of the tree, with the greatest toxicity occurring within the tree's dripline.'
Iowa State Univ. Extension & Outreach, Yard and Garden FAQ, 'What plants are sensitive to the juglone produced by black walnuts?', yardandgarden.extension.iastate.edu (read 2026-07-13): juglone-sensitive plants include 'members of the tomato family (tomato, potato, eggplant, pepper).'
remedy
Plant it outside the walnut's root zone — the whole drip line and beyond. There is no soil treatment for juglone.
A specialist pest or pathogen finds and builds on a continuous single-family host patch more readily than one broken by non-host families.
suboptimal if ignored → advise
Mechanism: Resource concentration - a specialist locates and holds its host more efficiently at higher host density and continuity, so an unbroken run of one family across adjacent beds is an easier target than the same family separated by a non-host (associational resistance).
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
Root 1973, 'Organization of a plant-arthropod association in simple and diverse habitats: the fauna of collards (Brassica oleracea)', Ecological Monographs 43:95-124 (abstract read by the maintainer 2026-08-21): proposes 'the resource concentration hypothesis, which states that herbivores are more likely to find and remain on hosts that are growing in dense or nearly pure stands; that the most specialized species frequently attain higher relative densities in simple environments.' This is another rule here's claim and mechanism verbatim.
Elmstrom, Andow & Barclay 1988, 'Flea beetle movement in a broccoli monoculture and diculture', Environmental Entomology 17(2):299-305 (read by the maintainer 2026-08-21): the empirical test on a brassica specialist (the flea beetle Phyllotreta cruciferae) - immigration ~1.3x faster into monocultures than into dicultures, emigration ~2x faster from dicultures - reported as 'strong, direct support for the hypothesis that host plants are harder to find and easier to lose in vegetationally diverse habitats than in monocultures.'
remedy
Where one family fills adjacent beds in a single season, breaking the run with a non-host family between them lengthens the distance the specialist must travel to the next host. Disclosed, never docked: a continuous single-family block can be the right call anyway - a wind-pollinated crop like corn sets better massed - so the app names the trade-off and leaves the choice to the gardener.
Cold-hardy annuals can be sown or transplanted before the last spring frost — hardy crops about three weeks before, half-hardy about two weeks before. Tender crops wait for the frost itself.
suboptimal if ignored → advise
Mechanism: Cold hardiness. Hardy crops tolerate hard frost and half-hardy crops tolerate light frost, so they can occupy the ground weeks before frost-tender crops are allowed in. The offset is measured from the last spring frost.
Evidence: confirmed against 4 sources in the research-based literature.
the 4 sources
University of Illinois Extension, 'Time Your Vegetable Plantings by Cold Hardiness' (2018-03-26), extension.illinois.edu/blogs/ilriverhort/2018-03-26-time-your-vegetable-plantings-cold-hardiness: very hardy vegetables 'withstand freezing temperatures and hard frosts without injury' (planted earliest in spring); frost-tolerant vegetables 'can withstand light frosts, but not freezing temperatures' (planted a couple of weeks later). LLM-summarised from a read of the page; it establishes the CATEGORIES but states no week offsets.
Colorado State Univ. Extension, GardenNotes #720, 'Vegetable Planting Guide', extension.colostate.edu/resource/vegetable-planting-guide (read 2026-07-25): hardy vegetables go in 'As early as 2-4 weeks before the date of the average last spring frost'; semi-hardy 'As early as 0-2 weeks before the date of the average last spring frost'; tender from seed 'around the date of the average last spring frost'; very tender 'Typically 2+ weeks after'. This is the source that states the offsets in weeks.
Where this rule sits in that range: hardy at 3 weeks is mid-range of CSU's 2-4. Half-hardy at 2 weeks is the EARLIEST EDGE of CSU's 0-2 - the most aggressive planting CSU sanctions, not the middle of it. The rule is inside published guidance at both ends, but it leans early on the half-hardy side and a gardener following it in a cold spring is taking that boundary.
Do not import an offset from another publication's hardiness scheme without checking the category names: CSU has no 'very hardy' tier, so a '4-6 weeks before frost' figure written against a four-tier scheme does not describe CSU's 'hardy'. Categories are not comparable across sources.
Long-season warm crops are started indoors several weeks before the last frost and set out after it — tomato and tomatillo about six weeks ahead, pepper and eggplant about eight. Basil, six.
suboptimal if ignored → advise
Mechanism: A frost-tender crop with a long days-to-maturity cannot mature if it is only direct-sown after the last frost — the frost-free window is too short. A head start under cover buys the weeks the season lacks; the seedling is set out only once frost has passed — the transplant date is still frost-gated.
Evidence: confirmed against 2 sources in the research-based literature.
the 2 sources
University of Minnesota Extension, 'Starting seeds indoors', extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors: seed-starting chart gives tomato '5-6 weeks' and pepper and eggplant '9 weeks' before the outdoor planting date (warm crops set out after the last frost). Read 2026-07-19 (LLM-summarised); read by the maintainer 2026-07-25, which is the read that promoted this rule. Note what the corpus's per-crop values do with the sources: tomato 6 sits at the top of Minnesota's '5-6 weeks' and inside Illinois's '6-8'; pepper and eggplant 8 sit BELOW Minnesota's '9 weeks' and at the top of Illinois's '6-8'. They are a reconciliation of two published ranges, not a figure either source prints.
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.
