August is harvest month in Zone 5 — tomatoes, peppers, corn and squash all peak now — and it is also the last serious sowing month for fall crops. The average first frost of Oct 1–15 is only about eight weeks away, so August sowings must be fast-maturing.
What August means in Zone 5
Zone 5 winters are genuinely cold, with average annual minimum temperatures of -20 to -10°F, and the growing season is short and precious. Every week counts, so May gardeners work fast once the last frost passes. The frost-free season lasts about five months, from early May into early October. The average last spring frost falls in the Apr 15–May 1 range and the average first autumn frost in the Oct 1–15 range — USDA zone averages, not exact dates, so check your local extension service before planting tender crops outside. Our planting calendar by ZIP turns them into a month-by-month plan.
Zone 5's frost-free season runs roughly from early May into early October, and August sits right at the pivot: summer crops are giving their biggest yields while the fall garden gets its final plantings. Spinach (40–50 days), radishes (25–40 days) and lettuce (45–60 days) sown in early August will be ready before the first frost, but anything slower than about 60 days is now too late to sow outdoors.
August task list
- Harvest daily — August abundance turns to waste fast. 2. Sow fast fall crops in the first two weeks of August. 3. Preserve the glut: freeze beans and corn, can tomatoes, dry herbs. 4. Keep watering deeply; August heat dries soil fast. 5. Order garlic and spring bulbs now. 6. Start a compost pile with spent summer plants (not diseased ones).
What to start indoors now
Indoor starting winds down in August, but a few jobs remain. Start lettuce and spinach indoors in trays if your garden soil is too hot and dry for good germination, then transplant the seedlings out when they have two true leaves. Start herbs like parsley and chives indoors for windowsill growing through winter. And start planning — order garlic now for September planting, since the best varieties sell out early. Use clean pots and fresh seed-starting mix, give seedlings strong light, and keep the soil moist but never waterlogged. Work out exact sowing dates with the seed-starting calculator.
What to direct-sow outdoors
Direct sow fast fall crops in early August: spinach, radishes, lettuce, arugula (30–45 days), turnips (40–60 days) and mustard greens (40–50 days). Sow a last round of cilantro and dill. These cool-season crops actually prefer August's shortening days to July's heat. Keep the seed bed moist until germination — a board or burlap over the row holds moisture and shades the soil. Prepare the bed first — fork it over, remove weeds, rake it level — then sow thinly, water gently, and thin seedlings to the spacing in the table below.
What to transplant now
Transplant the fall brassicas started indoors in June and July — broccoli, cabbage and kale — into their final spots in early August if they are not already out. Water deeply at transplanting and mulch well. This is the last transplanting window for fall crops in Zone 5; anything set out after mid-August will struggle to mature before the Oct 1–15 first frost. Harden seedlings off for a week first, plant on a cloudy day or in the evening, water them in well, and mulch around — but not against — the stems.
What to harvest this month
August is the biggest harvest month of the Zone 5 year. Tomatoes (60–85 days) are in full production, sweet corn (60–90 days) is ready when the silks turn brown, peppers (60–90 days) are colouring, and zucchini, cucumbers and green beans need picking every day or two. Start harvesting onions when their tops fall over, and cure them in a dry, airy place for two weeks before storing. Harvest in the morning, when plants are cool and crisp, and pick little and often — regular picking keeps most vegetables producing.
Frost protection in Zone 5
The average first frost of Oct 1–15 is close enough to plan around: count backwards from it to decide what can still be sown. A crop needing 40 days sown on August 20 finishes around September 29 — just in time. Frost cloth and row cover bought now will extend the fall harvest by weeks, protecting lettuce and spinach through the first light frosts. Tender crops like tomatoes and peppers will be killed by the first hard frost, so have a plan to pick green tomatoes and bring peppers in. When a cold night is forecast, water the soil in the afternoon, cover tender plants with frost cloth before sunset, and remove the covers in the morning. The Harvest Date Calculator can help you time plantings around your frost dates.
Planting data for August in Zone 5
All figures below are broad published ranges from standard horticultural references, not exact figures — they vary by variety, climate and soil.
| Crop | Action this month | Days to maturity | Notes |
|---|---|---|---|
| Spinach | Direct sow for fall | 40–50 | Sow early August; prefers cool soil |
| Radishes | Direct sow | 25–40 | Fastest fall crop; ready in a month |
| Tomatoes | Peak harvest | 60–85 | Pick ripe; pick green before frost |
| Sweet corn | Harvest | 60–90 | Ready when silks turn brown |
| Arugula | Direct sow | 30–45 | Sow in shade; harvest young leaves |
| Onions | Harvest + cure | 90–120 | Cure 2 weeks in dry, airy spot |
Browse the full planting calendar hub for every Zone 5 month, and see the neighbouring months in this zone:
Frequently asked questions
What can I plant in August in Zone 5?
Fast fall crops only: spinach, radishes, lettuce, arugula, turnips and mustard greens sown in early August. Anything needing more than about 60 days is too late to sow outdoors in Zone 5.
When is the first frost in Zone 5?
The average first autumn frost falls between Oct 1 and Oct 15. These are USDA zone averages, not exact dates — check your local extension service and the forecast as autumn approaches.
What should I harvest in August in Zone 5?
Tomatoes, sweet corn, peppers, zucchini, cucumbers, green beans and onions. Harvest daily — in August, a zucchini or cucumber left an extra day can double in size.
How do I preserve the August glut?
Freeze blanched beans and corn, can or freeze tomatoes, dry herbs by hanging them in bunches, and cure onions and winter squash for storage. Process produce the day you pick it for the best quality.
Is August too late to plant garlic in Zone 5?
Yes — garlic is planted in late September or October in Zone 5. Order your seed garlic in August, since the best varieties sell out, and plant it a few weeks before the ground freezes.