Last Frost Date Richmond Hill — April 28 (Zone 6b)

Richmond Hill's last spring frost date is April 28 for the central core — Zone 6b. This is the historical 50th-percentile average from Environment and Climate Change Canada climate normals (1991–2020). South Richmond Hill (Mill Pond area, Lake Wilcox south, Yonge/Highway 7 corridor) runs 2–3 days earlier (April 25–28). North Richmond Hill on the Oak Ridges Moraine (Oak Ridges, Jefferson, north Bayview) runs 3–5 days later (May 1–5) because the moraine sits at significantly higher elevation (300 m vs 200 m for south Richmond Hill). The full historical range spans April 12 (earliest) to May 12 (latest).

Wait until May 5–15 to transplant tomatoes, peppers, basil, beans, and squash in central and south Richmond Hill. Oak Ridges Moraine neighbourhoods (Oak Ridges, Jefferson, north Bayview Hill) should wait until May 10–20 due to elevation. Cool-season crops (lettuce, peas, brassicas) can be direct sown from late March. Victoria Day weekend (third Monday of May) is the safe-transplant deadline across the GTA. The growing season is approximately 180 days in central Richmond Hill and 170 days on the Oak Ridges Moraine.

Richmond Hill neighbourhoods vary by elevation and position on the Oak Ridges Moraine. Mill Pond (south, central core): April 25–28. Yonge/Highway 7 corridor: April 26–29. Bayview Hill (south): April 26–29. Lake Wilcox area: April 27–30. Central Bayview / Bayview Glen: April 28–May 1. Jefferson (Oak Ridges Moraine): May 1–5. Oak Ridges (north on moraine): May 2–6. North Bayview Hill: May 1–5. The Oak Ridges Moraine elevation effect adds roughly 5–7 days to last-frost dates compared to lower-elevation south Richmond Hill.

Richmond Hill is officially Zone 6b for the central and south parts under the Canadian Plant Hardiness Zone system. The Oak Ridges Moraine portion (north Richmond Hill) sits in the cooler end of Zone 6b approaching Zone 6a at higher elevations. Rural areas immediately north of Richmond Hill (King City, Aurora) are Zone 6a. A Zone 6 plant will reliably overwinter anywhere in Richmond Hill; Zone 7 plants survive most years in south Richmond Hill protected spots but die in severe polar-vortex winters.

The Oak Ridges Moraine is a 160 km long ridge of glacial sediment running east-west across the GTA, rising to about 300 m elevation through north Richmond Hill, Oak Ridges, and Jefferson neighbourhoods. The elevation difference vs central Richmond Hill (~200 m) translates to roughly 2–3°C cooler night temperatures in spring, producing 5–7 days of later last-frost dates and slightly later autumn first frost. Oak Ridges and Jefferson essentially have a different microclimate than south Richmond Hill despite being only 5–7 km apart. The moraine also produces more reliable snow cover in winter, which protects perennial plants from polar-vortex temperature extremes.

Late frost in Richmond Hill can drop to -3°C in worst cases. Floating row cover (Reemay, Agribon) over transplants protects to about -3°C. Cloches or inverted pots over individual seedlings. Heavy mulch around transplants. Plant tender crops in the warmest spot — south-facing fence, against a heat-radiating brick wall. Don't transplant tender crops if nights below 3°C are forecast through May 12. Available at Sheridan Nurseries Richmond Hill, Plant World, Home Depot, Canadian Tire.