Your growing season is not fixed. With a few layers of protection, most gardeners can add 4–8 weeks on each end — and in mild-winter climates, harvest straight through.
The protection ladder (each layer buys roughly 2–4°F... and degrees are weeks):
Row cover (floating fabric) — the workhorse. Lightweight fabric laid directly over plants buys 2–4°F of frost protection and doubles as insect barrier. Heavyweight versions buy 6–8°F. Cost: ~$15 for a 50-foot roll, reusable for years.
Low tunnels — row cover or clear plastic over wire hoops. Easy to vent on warm days (plastic tunnels can hit 90°F inside on a sunny 50°F day — vent or cook your crop).
Cold frames — a bottomless box with a clear lid, facing south. Essentially a suitcase-sized greenhouse for hardening off seedlings and overwintering greens.
Deep mulch + harvest-in-place — carrots, leeks, and parsnips hold in the ground under a foot of straw well past hard frost. Dig as needed; cold storage without a root cellar.
Match the crop to the tactic: Protection extends the season for crops that can already ALMOST handle it. Spinach, kale, mâche, and carrots under a low tunnel will feed you in December in zone 6. A tomato under the same tunnel is still dead by Thanksgiving — frost-tender crops end at frost, full stop.
The spring side: Pre-warm soil with clear plastic for two weeks before your last frost, and you can plant cool-season crops 3–4 weeks early into soil that's actually ready. Wall-o-water style cloches let zone gamblers set out tomatoes 2–3 weeks early with real protection.
Watch your frost dates: All of this math anchors to your first and last frost dates — the ones on your plan header. Protection shifts your effective dates; it doesn't repeal them.
Quick wins: Buy one roll of medium-weight row cover this fall. Throw it over your greens bed the night before the first frost warning, and eat salads a month longer than your neighbors.