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

Planting zone for 97758 — Riley, OR

ZIP code 97758 (Riley, Harney County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is June 11 and the first fall frost September 28.

Where ZIP 97758 is

Outlined: the ZIP code area · 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.

Zone6a−10 to −5 °F

Coldest night−23.3 to −20.6 °C

Last frostJun 11

First frostSep 28

2012 zone6b

Was 6b on the 2012 map — half a zone colder now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Riley, OR…

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 in Riley, OR

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostJune 11median — 50% chance of a later frost

Safe for tender plantsJune 28only 10% chance of frost after

First fall frostSeptember 28median — 10% chance by Sep 3

Growing season107 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 24 and returns around October 13.

From the NOAA station Squaw Butte-Northern Great Bas, OR — 4 miles away, elevation 4,659 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 97758

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 30 – May 14

SpinachSow outdoors · Apr 30 – May 21

Broccoli, cabbageStart indoors · Apr 2 – Apr 16

Broccoli, cabbageTransplant · May 21 – Jun 4

Onion setsPlant outdoors · May 14 – May 28

PotatoesPlant outdoors · May 21 – Jun 4

LettuceSow outdoors · May 14 – May 28

Carrots, beetsSow outdoors · May 21 – Jun 4

TomatoesStart indoors · Apr 16 – Apr 30

TomatoesTransplant · Jun 18 – Jul 2

Peppers, eggplantStart indoors · Apr 2 – Apr 16

Peppers, eggplantTransplant · Jun 25 – Jul 9

BeansSow outdoors · Jun 18 – Jul 2

Sweet cornSow outdoors · Jun 18 – Jul 2

Cucumbers, squashSow outdoors · Jun 18 – Jul 2

Fall lettuce, spinachSow outdoors · Aug 3 – Aug 17

GarlicPlant cloves · Sep 14 – Oct 19

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Jun 11) and first fall frost (Sep 28) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 97758 came on Mar 27 — 18 days earlier than the 1991–2020 average (Apr 14).

average
Apr 142026
Mar 27

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 6a in Oregon

607 plants native to the lower 48 states, recorded in Oregon, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. Each links to its USDA PLANTS profile.

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Riley, OR.

Soil in Riley, OR

The soil mapped at the center of ZIP 97758 is Actem — cobbly loam, well drained.

TextureCobbly loama good balance for most vegetables

pH7.0neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter1.5%low — add compost

Hydrologic groupDwater soaks in very slowly

Farmland classFarmland of statewide importanceUSDA classification

Map unit: Actem cobbly loam, 2 to 20 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 97758; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Riley, OR

Summer high84 °Faverage high, July

Winter low20 °Faverage low, December

Hot days22days a year at 90 °F or more

Freezing nights180nights a year at 32 °F or less

Growing degree days1,836base 50 °F — the season’s usable heat

Longest day15 h 25 mindaylight on June 21

Shortest day8 h 57 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation11.9 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Squaw Butte-Northern Great Bas, OR (4 mi away); precipitation: Squaw Butte-Northern Great Bas, OR (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

Christmas Valley, OR · 40 mi

977516a

Paulina, OR · 47 mi

976406b

Summer Lake, OR · 50 mi

977526a

Post, OR · 52 mi

978206b

Canyon City, OR · 56 mi

977546b

Prineville, OR · 60 mi

Oregon planting zones →

Questions about 97758

What planting zone is ZIP code 97758?

ZIP code 97758 (Riley, OR) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in Riley, OR?

The median last spring frost (32 °F) near 97758 is June 11; after June 28 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Squaw Butte-Northern Great Bas station.

When is the first frost in Riley, OR?

The median first fall frost near 97758 is September 28, giving a median frost-free growing season of 107 days.

When should I plant tomatoes in 97758?

Start tomato seeds indoors around Apr 16 – Apr 30 and set transplants outside around Jun 18 – Jul 2, one to three weeks after the median last frost.

How much rain and snow does 97758 get?

About 11.9 inches of precipitation a year (NOAA 1991–2020 normals, Squaw Butte-Northern Great Bas station).

How hot do summers get in Riley, OR?

The average high peaks at 84 °F in July, with about 22 days a year at 90 °F or more.

What kind of soil does 97758 have?

The USDA soil survey maps Actem at the center of ZIP 97758: cobbly loam, well drained, pH about 7.0 (neutral).

Did spring come early in Riley, OR in 2026?

Spring leaf-out near 97758 came on Mar 27 in 2026, 18 days earlier than the 1991–2020 average (Apr 14), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Riley, OR?

Long-day onions: the longest day near 97758 is 15 h 25 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 97758 change?

Yes. The 2012 USDA map put 97758 in zone 6b; the 2023 map puts it in zone 6a. The newer map uses 1991–2020 data and more weather stations.