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

Planting zone for Mill Valley, CA

Mill Valley, CA is in USDA zone 10a across its 2 ZIP codes.

Mill Valley on the zone map

Outlined: its 1 ZIP code areas · 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.

Zone10a30 to 35 °F

ZIP codes2

Last frostrare

First frostrare

Growing seasonall year

10a 2 ZIPs

Frost forecast — next 7 nights

live from the National Weather Service

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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

A 32 °F frost doesn't happen here in most winters. At the nearest station (NOAA station Kentfield, CA, elevation 144 ft) the median growing season is 334 days. When frost does come, it is a midwinter night or two; cover tender plants when a freeze is forecast.

Frost data: NOAA NCEI U.S. Climate Normals 1991–2020.

When spring arrived in 2026

In 2026, spring leaf-out near 94941 came on Jan 24 — 6 days earlier than the 1991–2020 average (Jan 30).

average
Jan 302026
Jan 24

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).

Soil in Mill Valley, CA

The soil mapped at the center of ZIP 94941 is Maymen — gravelly loam, somewhat excessively drained.

TextureGravelly loama good balance for most vegetables

pH5.5moderately acidic; most vegetables like 6.0–7.0

DrainageSomewhat excessively drainednatural drainage class

Organic matter0.75%low — add compost

Hydrologic groupDwater soaks in very slowly

Farmland classNot prime farmlandUSDA classification

Map unit: Maymen-Maymen variant gravelly loams, 30 to 75 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 94941; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Mill Valley, CA

Summer high83 °Faverage high, July

Winter low42 °Faverage low, January

Hot days27days a year at 90 °F or more

Freezing nights5nights a year at 32 °F or less

Growing degree days3,578base 50 °F — the season’s usable heat

Longest day14 h 48 mindaylight on June 21

Shortest day9 h 32 mindaylight on December 21

Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully

Precipitation36.2 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: Kentfield, CA (4 mi away); precipitation: Muir Woods, CA (2 mi away). Daylight is calculated from latitude.