Canadian Gardening Terms — Glossary & Tools

The average spring date after which a killing frost is unlikely — the green light to set out tender crops. An average, not a guarantee.

The average fall date of the first killing frost — the deadline to harvest or protect tender crops before the season ends.

The average number of days between last spring and first fall frost — the window a crop must mature in.

Effectively the same as frost-free days — how long you can grow frost-sensitive crops outdoors in your city.

The date with a set probability of frost. Serious growers plant to the 10% date (~90% safe), not the average.

A running total of heat above a base temperature — a better predictor of crop timing and viability than the calendar.

Frost that forms on a clear, calm night as the ground radiates heat away — it can strike above the thermometer reading.

Using row covers, cloches, cold frames, and mulch to start earlier and harvest later than the open-ground season allows.

Canada’s 0–8 rating of what perennials/shrubs/trees survive winter — it weighs heat, snow, and wind, not just cold.

The American system, based on winter minimum only. A USDA number is NOT the same as a Canadian zone — don’t plant by US lists here.

A small pocket warmer or colder than its zone — a sheltered south wall, a frost-pocket low spot — that can shift what you can grow.

A warm Alberta wind that can raise winter temperatures 15–20 °C in hours — welcome, but its freeze-thaw swings stress plants.

A named, cultivated variety of a plant (e.g. ‘Limelight’ hydrangea). Hardiness varies by cultivar, so the name matters.

Cold tolerance: tender = frost kills it; half-hardy = takes a light frost; hardy = survives frost (and winter, if zone-matched).

Gradually acclimatizing indoor seedlings to sun, wind, and cool nights over ~7–10 days before transplanting, so they don’t shock.

Days from seeding (or transplant) to harvest. Match it against your frost-free days so the crop finishes before fall frost.

Direct sow = seed straight into the garden; transplant = start indoors and move out. Cold climates start heat-lovers indoors.

Sowing the same crop in staggered batches (or following one crop with another) for a continuous harvest instead of one glut.

When a cool-season crop (lettuce, spinach, cilantro) shoots up to flower and turns bitter in summer heat — sow early or in cooler windows.

A required cold period some plants need to trigger growth or flowering — why garlic is planted in fall to chill over winter.

pH is soil acidity/alkalinity (it governs nutrient uptake); an amendment (compost, lime, sulphur) adjusts soil to suit a crop.

A surface layer (bark, straw, leaves) that holds moisture, blocks weeds, moderates soil temperature, and protects crowns over winter.

Where a shrub sets flower buds — it decides pruning timing. Old wood: prune after bloom. New wood: prune in late winter.

Is a Canadian hardiness zone the same as a USDA zone?

No. Canada uses the NRCan system (0–8), which weighs summer heat, rainfall, snow, and wind — not just winter minimum temperature like the USDA system. The numbers don’t line up, so US “cold-hardy” plant lists can mislead you. Always use your NRCan zone.

What’s the difference between the last frost date and the frost-free season?

The last frost date is a single spring date (when it’s safe to plant tender crops); the frost-free season is the whole window between last spring and first fall frost — the number of days a crop has to mature.

Why won’t my hydrangea (or lilac) bloom after I prune it?

Almost always because it blooms on old wood and you pruned at the wrong time — cutting off the buds it already set. Old-wood shrubs are pruned right after they flower. The pruning calendar sorts every shrub into old-wood vs new-wood.