Gardeners around Halifax have one job before the sun goes down tonight. Environment Canada issued a frost advisory for all of mainland Nova Scotia at 10:56 a.m. Saturday, warning that conditions favour frost developing overnight, with lows between zero and plus 5 by early Sunday morning.

The coldest readings are expected in low-lying areas. That means a garden in a hollow or a low corner of the yard can frost over even when the city’s forecast sits a few degrees higher. The Weather Network has Halifax at a low of 5 tonight, feeling like 2.

It’s early for this. Based on Environment Canada climate normals from the Citadel weather station, the Old Farmer’s Almanac puts Halifax’s average first fall frost on Oct. 20, so tonight comes about 10 days ahead of the usual date.

Environment Canada’s advice is short: take steps to protect cold-sensitive plants, trees and crops, and cover plants, especially in frost-prone spots. Anything in a pot or hanging basket can simply come inside for the night.

For plants that stay in the ground, the gardening researchers behind Garden Professors suggest a loose bed sheet or similar light fabric rather than plastic. Keep the cover off the leaves, because foliage pressed against a cold cover can freeze anyway. A few stakes or a simple frame over a vegetable bed will hold the sheet up.

The covers should come off Sunday morning once it starts to warm up. Sun on a covered plant can build heat quickly enough to damage new growth.

The chill doesn’t stick around. Saturday tops out near 12 under sunny skies with northwest winds around 44 km/h, Sunday reaches 13 with a mix of sun and cloud, and Thanksgiving Monday climbs to 16, with a chance of a few showers in the morning.

The advisory covers tonight into early Sunday. Environment Canada posts any changes on its public alerts page.