Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 00978 — St Just, PR

ZIP code 00978 (St Just, Trujillo Alto County) is in USDA zone 13a: the coldest winter night averages 60 to 65 °F.

Where ZIP 00978 is

tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone13a60 to 65 °F

Coldest night15.6 to 18.3 °C

Last frostrare

First frostrare

2012 zone—

The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 13a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for St Just, PR…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates

Frost is rare or absent here: St Just, PR is in zone 13a, where the coldest night of a typical winter stays above freezing. Cool-season vegetables grow best from fall through spring; summer heat, not frost, is the limit.

Soil in St Just, PR

The soil mapped at the center of ZIP 00978 is Vega Alta — clay loam, well drained. Much of the area is built over (urban land); this is the natural soil underneath.

TextureClay loamholds water and nutrients; slow to drain and warm up

pH5.4strongly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter3.6%moderate

Hydrologic groupCwater soaks in slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Urban land-Vega Alta complex, 2 to 12 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 00978; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in St Just, PR

Longest day13 h 14 mindaylight on June 21

Shortest day11 h 01 mindaylight on December 21

Onions to growShort-daysummer days stay under about 14 h 20 min, so long-day varieties won’t bulb

Daylight is calculated from latitude.

Nearby ZIP codes

1 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

Trujillo Alto, PR · 3 mi

Puerto Rico planting zones →

Questions about 00978

What planting zone is ZIP code 00978?

ZIP code 00978 (St Just, PR) is in USDA hardiness zone 13a on the 2023 map: the coldest night of an average winter reaches 60 to 65 °F (15.6 to 18.3 °C).

What kind of soil does 00978 have?

The USDA soil survey maps Vega Alta at the center of ZIP 00978: clay loam, well drained, pH about 5.4 (strongly acidic).

What kind of onions grow in St Just, PR?

Short-day onions: the longest day near 00978 is 13 h 14 min, so summer days stay under about 14 h 20 min, so long-day varieties won’t bulb.