Butterhead lettuce · Berwyn, Illinois, United States
When to plant butterhead lettuce in Berwyn
Main outdoor window
25 Mar - 8 Apr
A climate estimate. Check your soil, forecast and cultivar.
Timed from last spring frost
4 April
In Berwyn, on your chosen risk.
Ready to pick
1 May - 31 Oct
If you plant at the start of the window.
The average last frost. Half of all years are later than this.
Step by step in Berwyn
Download these planting dates (.ics)
Import into Apple Calendar, Google Calendar or Outlook. Dates use the selected risk level and are planning estimates, not frost alerts.
Each window is a planning range. Check the forecast, soil and cultivar before planting; a later date is not automatically safer in hot or wet conditions.
Start indoors
21 Feb - 7 Mar
Six weeks before your last frost, under cover or on a windowsill.
Sow for autumn
14 Aug - 4 Sep
Counting back 74 days from your first frost so the crop matures in time.
Sow direct
25 Mar - 8 Apr
Delayed by a soil-warming estimate derived from historical air temperatures. The frost-only date would be 14 Mar. Measure your soil before planting.
Sow direct
25 Mar - 8 Apr
Delayed by a soil-warming estimate derived from historical air temperatures. The frost-only date would be 21 Mar. Measure your soil before planting.
Harvest
1 May - 31 Oct
Butterhead lettuce through the year
Against the frost risk in Berwyn
Seasonal context
Rainfall and the growing season in Berwyn
May has the highest average precipitation (119 mm); January has the lowest (47 mm). Compare this pattern with the planting windows and your water supply.
During wetter months, check that beds and containers drain after heavy rain. During drier months, plan how you will keep seeds and new transplants watered. Monthly averages can hide long dry spells and intense storms; they do not show soil moisture, humidity or this week's weather.
Source: NASA POWER, corrected MERRA-2 precipitation, 2001–2020. Values are approximate monthly totals, including the water equivalent of snow, from the nearest 0.5° × 0.625° grid cell. This reference period differs from the temperature record. Rainfall provides context and does not change the calculated planting dates. Method and limitations.
Monthly growing conditions in Berwyn
Compare the planting window with the local temperature pattern. These are historical monthly averages, not this year's forecast or measured soil temperatures. Average frost days do not tell you whether a particular night will freeze.
| Month | Average low | Average high | Frost days |
|---|---|---|---|
| January | -4.9°C (23.2°F)23.2°F (-4.9°C) | -0.2°C (31.7°F)31.7°F (-0.2°C) | 25.7 |
| February | -4.5°C (24°F)24°F (-4.5°C) | 0.8°C (33.5°F)33.5°F (0.8°C) | 23.6 |
| March | -0.5°C (31°F)31°F (-0.5°C) | 5.1°C (41.2°F)41.2°F (5.1°C) | 16.9 |
| April | 3.8°C (38.8°F)38.8°F (3.8°C) | 10°C (50°F)50°F (10°C) | 2.7 |
| May | 8.8°C (47.8°F)47.8°F (8.8°C) | 15.2°C (59.3°F)59.3°F (15.2°C) | 0.0 |
| June | 15.1°C (59.1°F)59.1°F (15.1°C) | 21.1°C (70°F)70°F (21.1°C) | 0.0 |
| July | 19.6°C (67.3°F)67.3°F (19.6°C) | 24.9°C (76.8°F)76.8°F (24.9°C) | 0.0 |
| August | 20°C (68.1°F)68.1°F (20°C) | 25.1°C (77.1°F)77.1°F (25.1°C) | 0.0 |
| September | 16.4°C (61.5°F)61.5°F (16.4°C) | 22°C (71.6°F)71.6°F (22°C) | 0.0 |
| October | 9.9°C (49.7°F)49.7°F (9.9°C) | 15.6°C (60°F)60°F (15.6°C) | 0.0 |
| November | 3.4°C (38.2°F)38.2°F (3.4°C) | 8.5°C (47.3°F)47.3°F (8.5°C) | 5.5 |
| December | -1.8°C (28.9°F)28.9°F (-1.8°C) | 2.7°C (36.8°F)36.8°F (2.7°C) | 18.4 |
For butterhead lettuce, also check drainage, sunlight and cultivar requirements. See the rainfall context above; humidity, irrigation and local pest pressure are not calculated.
Local growing check
Before choosing butterhead lettuce for Berwyn
- May is the wettest month in the rainfall grid, averaging about 119 mm. Check how your own bed drains and plan watering around actual soil moisture; monthly rain totals are not an irrigation schedule.
The temperature and rainfall tables on this page show the underlying climate estimates. How these suitability checks work · Record what happens in your garden.
Before you plant butterhead lettuce
Use the calendar to plan ahead, then check the conditions in your own garden.
- Measure the soil at sowing depth. Aim for at least 4.5°C (40.1°F); the calendar estimates soil warmth from air temperatures and cannot measure your bed.
- Check the local overnight forecast before planting out. Delay planting or keep protection ready if frost is forecast, even after the historical last-frost date.
- Harden off plants raised indoors: gradually expose them to outdoor light, wind and temperature before their final move into the bed.
- Use the maturity range on your seed packet when choosing a variety. Cold, short days and transplant stress can make harvest later than the calendar estimate.
Protect the soft head from crowding and water stress
Leave enough room for the outer leaves and keep the root zone evenly moist. In hot conditions, compare a heat-suitable variety or cooler position; drought can bring bitterness and bolting.
Harvest the head gently and use it promptly, or take modest numbers of outer leaves while the centre continues to grow. Succession sowing is more useful than leaving mature soft heads indefinitely in the bed.
What to record this season
How many mature heads could you use before quality declined? Add the cultivar, sowing date and conditions to your growing record so you can compare next season.
Further reading: RHS lettuce growing guide . General crop guidance; local dates on this site are calculated separately. Source checked 19 September 2026 by Safe to Plant; this is not an expert review.
The RHS guide is written for UK growing conditions. Use its cultivation advice with local cultivar and seasonal guidance; its calendar months are not worldwide recommendations.
How the dates are calculated and their limits · Keep a growing record · Report a local discrepancy
Why these dates
Leave enough room for the outer leaves and keep the root zone evenly moist. In hot conditions, compare a heat-suitable variety or cooler position; drought can bring bitterness and bolting.
Protect tender growth from frost and wait for suitable growing warmth. The catalog cold-damage figure is a reference, not a guarantee: duration, wind, plant age and acclimatisation affect damage.
This calendar uses frost-relative offsets as a starting point. Butterhead lettuce are timed from 6 weeks before that frost for an indoor start, with planting out 2 weeks before it, and this page simply resolves those offsets against the frost date computed for Berwyn.
The calendar also applies a soil-warming estimate derived from historical air temperatures. Where that estimate is later than the frost-based date, it delays the window. Soil in your own garden can warm earlier or later; a thermometer at sowing depth is a better final check. Cold, wet conditions can slow germination and increase decay risk.
The median frost-free season here is 227 days, against 45 to 60 days to maturity for this crop counted from sowing. That margin is what decides whether a late sowing is worth attempting.
Also in Berwyn
Other vegetables to time
Growing butterhead lettuce in Berwyn
Can I grow butterhead lettuce in Berwyn?
The calendar estimates a planting window, not a guarantee of success. May is the wettest month in the rainfall grid, averaging about 119 mm. Check how your own bed drains and plan watering around actual soil moisture; monthly rain totals are not an irrigation schedule.
When should I plant butterhead lettuce in Berwyn?
Aim for 25 Mar - 8 Apr in an average year. If you would rather not gamble on the weather, wait until 3-17 Apr - by then frost has finished in nine years out of ten.
Can I plant butterhead lettuce earlier in Berwyn?
The historical frost estimate is 14 Mar. For Butterhead lettuce, an air-temperature model estimates soil warmth of about 4.5°C (40.1°F) around 25 Mar. This is not a soil measurement or a forecast. Check your bed at sowing depth; cold, wet conditions can slow growth and increase decay risk.
When might butterhead lettuce be ready to harvest in Berwyn?
The estimated period is 1 May - 31 Oct, based on 45 to 60 days from the modeled planting date. Cultivar, planting material and growing conditions can change this interval; check the plant as well as the calendar.
How much frost will butterhead lettuce tolerate?
Protect tender growth from frost and wait for suitable growing warmth. The catalog cold-damage figure is a reference, not a guarantee: duration, wind, plant age and acclimatisation affect damage.