Gardening glossary
Microclimate
Every garden contains several microclimates, and learning to read them is one of the highest-leverage skills a gardener can develop. A single property can simultaneously host a spot that's effectively Zone 8 (south-facing wall, paved patio reflecting heat) and a spot that's effectively Zone 6 (low-lying corner where cold air pools).
Common microclimate drivers:
- **Aspect.** A south-facing slope or wall in the Northern Hemisphere receives 20–30% more direct sun and can be 5–10°F warmer than a north-facing one. Reverse for the Southern Hemisphere. - **Thermal mass.** Brick walls, concrete patios, and stone paths absorb heat during the day and release it at night, raising local minimum temperatures and reducing frost risk. - **Cold-air drainage.** Cold air is denser and flows downhill. A walled garden at the bottom of a slope often becomes a **frost pocket** where the last spring frost arrives 1–2 weeks later than at higher ground 50 meters away. - **Wind exposure.** Windy sites desiccate plants and effectively lower the temperature plants experience. Hedges and walls create lee zones that can extend the season noticeably. - **Proximity to water.** Large bodies of water moderate temperatures, suppressing late frosts in spring and extending the season in fall. - **Urban heat island.** City gardens average 2–5°F warmer than rural ones nearby — enough to push central London into a different RHS hardiness band from the surrounding Home Counties.
Practical implications:
- Push borderline-hardy plants (figs, citrus in pots, rosemary in cold zones) against a south-facing wall. - Plant tender crops on raised beds or higher ground rather than low corners. - Keep frost-sensitive seedlings out of obvious frost pockets even when the regional forecast looks safe.
I always tell Growli users to walk the garden at dawn after a cold night in early spring — you can literally see the frost outline where the microclimates draw their boundaries.