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Gardening glossary

Growing season

Growing season is the most practical measurement of "how much gardening time do I have." For most temperate gardeners it's defined as the number of frost-free days — the gap between the last spring frost and the first fall frost. But the fuller definition also factors in soil temperature and average daily highs above the threshold a given crop actually needs to grow.

Typical frost-free season length:

- **USDA Zone 3** (northern Minnesota, central Alaska): 90–110 days - **USDA Zone 5** (Chicago, Denver, much of New England): 140–160 days - **USDA Zone 7** (Washington DC, Portland OR, most of England): 180–210 days - **USDA Zone 9** (central Florida, coastal California): 280+ days - **USDA Zone 10–11**: effectively year-round

Why it matters: every vegetable has a **days-to-maturity** number on the seed packet, and that number assumes the plant is in active growing conditions the whole time. A 90-day tomato variety in a 110-day Zone 4 garden gives you only 20 days of buffer — one cold spring or early frost wipes out the harvest. In the same garden, a 120-day variety like an heirloom beefsteak simply won't ripen outdoors without a tunnel.

Two adjustments I always recommend in the Growli app:

1. **Soil temperature, not just air.** Tomatoes need soil ≥ 60°F to actually root and grow, which is usually 2–3 weeks after the last frost. The "frost-free" window overstates the usable season for warm-season crops. 2. **Season extension.** Row cover, low tunnels, and cold frames can add 3–5 weeks on each end. A Zone 5 gardener with a polytunnel effectively gardens in Zone 6b conditions.

Cool-season crops (lettuce, spinach, peas, brassicas, garlic) ignore the conventional growing season and grow happily in shoulder weeks where warm-season crops would stall.

Where this comes up in our guides

Related terms

Frost date

A frost date is the average calendar date when air temperature at your location is expected to drop to 32°F (0°C). Gardeners use two: last spring frost and first fall frost, which together define the frost-free growing window.

Last frost

The last frost (or last spring frost) is the average date of the final freezing temperature of spring at your location. It is the anchor date for transplanting frost-tender crops — tomatoes, peppers, basil, beans, and squash — outdoors.

First frost

The first frost (or first fall frost) is the average date of the season's first freezing temperature in autumn. It ends the growing season for warm-weather crops and is the anchor date for planning final harvests, garlic planting, and cover-crop sowing.

Hardiness zone

A hardiness zone is a geographic band defined by average annual minimum winter temperature. The USDA system uses 13 zones in 10°F steps; in the UK, RHS H1–H7 ratings serve a similar purpose for perennials and shrubs.

Chill hours

Chill hours measure the cumulative time a fruit tree spends between roughly 32°F and 45°F (0–7°C) during winter dormancy. Deciduous fruit trees like apples, peaches, and cherries need a specific minimum to break dormancy and bloom normally in spring.