When to Plant Cornflowers in Wheaton, Illinois, United States

Step by step in Wheaton

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

15 Mar - 12 Apr

Six weeks before your last frost, under cover or on a windowsill.

Sow direct

5 Apr - 3 May

Three weeks before your last frost.

Plant out

12 Apr - 10 May

Two weeks before your last frost.

In flower

9-29 Jun

Sow in succession. A single sowing gives you a single glut. Sow a short row every 21 days through the window above and you get a steady supply instead.

Frost tolerance

Hardy

Damaged below

-10°C (14°F)

Days to flowering

65–85

Hardy to

Zone 2a–11a

Min soil temp

7°C (44.6°F)

Spacing

25 cm

Sowing depth

10 mm (0.4 in)

Sun

Full

Cornflowers through the year

Against the frost risk in Wheaton

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Cornflowers

Frost risk Start indoors Sow direct Plant out Harvest Today

Seasonal context

Rainfall and the growing season in Wheaton

May has the highest average precipitation (121 mm); January has the lowest (44 mm). Compare this pattern with the planting windows and your water supply.

Jan 44 mm

Feb 51 mm

Mar 63 mm

Apr 94 mm

May 121 mm

Jun 112 mm

Jul 100 mm

Aug 105 mm

Sep 87 mm

Oct 91 mm

Nov 58 mm

Dec 58 mm

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 Wheaton

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.

NASA POWER climate averages, 1995–2024
Month	Average low	Average high	Frost days
January	-9.8°C (14.4°F)	-1.5°C (29.3°F)	29.4
February	-8.2°C (17.3°F)	1.1°C (33.9°F)	26.6
March	-2.4°C (27.6°F)	7.7°C (45.9°F)	23.1
April	2.6°C (36.7°F)	14.5°C (58.1°F)	8.7
May	8.8°C (47.8°F)	20.7°C (69.3°F)	0.3
June	14.7°C (58.5°F)	26.3°C (79.3°F)	0.0
July	17.6°C (63.8°F)	28.7°C (83.6°F)	0.0
August	17.2°C (63°F)	28.3°C (83°F)	0.0
September	12.9°C (55.2°F)	24.7°C (76.4°F)	0.0
October	5.9°C (42.7°F)	17°C (62.6°F)	3.2
November	-0.7°C (30.7°F)	8.4°C (47.2°F)	18.0
December	-6.3°C (20.6°F)	1.4°C (34.5°F)	27.5

For cornflowers, 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 cornflowers for Wheaton

May is the wettest month in the rainfall grid, averaging about 121 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 cornflowers

Use the calendar to plan ahead, then check the conditions in your own garden.

Measure the soil at sowing depth. Aim for at least 7°C (44.6°F); the calendar estimates soil warmth from air temperatures and cannot measure your bed.
Frost tolerance does not make saturated or frozen soil suitable for planting. Wait until the bed can be worked without smearing or compacting it.
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.

Use the cooler season and manage self-seeding

Choose full sun or light shade with drainage. Too much shade can leave stems weak and leaning, while tall varieties may need support.

Avoid unnecessary fertilising: cornflowers tolerate relatively poor soil. Maintain moderate moisture while plants establish rather than leaving a new sowing to dry out.

Deadhead to limit self-seeding, or leave some seed heads where wildlife and natural reseeding are welcome. Check local planting guidance before allowing a non-native plant to spread.

Further reading: NC State Extension Plant Toolbox: cornflower . General crop guidance; local dates on this site are calculated separately. Source checked 18 September 2026 by Safe to Plant; this is not an expert review.

How the dates are calculated and their limits · Keep a growing record · Report a local discrepancy

Why these dates

Choose full sun or light shade with drainage. Too much shade can leave stems weak and leaning, while tall varieties may need support.

Check the named variety and local forecast before exposing young growth. The catalog cold-damage figure is a reference, not a guarantee: plant age, acclimatisation, wind and the duration of a freeze affect damage.

This calendar uses frost-relative offsets as a starting point. Cornflowers 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 Wheaton.

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.

Wheaton is zone 5b, within the crop's general range. This is an initial cold-hardiness check; cultivar, exposure, drainage and unusual winters can still change the outcome.

The median frost-free season here is 179 days, against 65 to 85 days to first flower for this crop counted from sowing. That margin is what decides whether a late sowing is worth attempting.

See every crop timed for Wheaton →

Nearby

Cornflowers in places close by

Naperville 10 km Schaumburg 19 km Bolingbrook 19 km Hoffman Estates 20 km Aurora 21 km Elgin 24 km

Also in Wheaton

Other flowers to time

Tulips very hardy Daffodils very hardy Dahlias tender Sunflowers tender Crocuses very hardy Peonies very hardy Calendulas hardy Hyacinths very hardy Sweet peas hardy Pansies very hardy Snowdrops very hardy Zinnias tender

Growing cornflowers in Wheaton

Can I grow cornflowers in Wheaton?

The calendar estimates a planting window, not a guarantee of success. May is the wettest month in the rainfall grid, averaging about 121 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 cornflowers in Wheaton?

Aim for 5 Apr - 3 May in an average year. If you would rather not gamble on the weather, wait until 21 Apr - 19 May - by then frost has finished in nine years out of ten.

When might cornflowers flower in Wheaton?

The estimated period is 9-29 Jun, based on 65 to 85 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 cornflowers tolerate?