The below list is based on 30 years of experience and informal trial and error. We hope you can benefit from our knowledge!
JAN - Too cold for good establishment, risk of death in prolonged freezing weather in first week after planting. Not recommended.
FEB - Can be planted if weather above freezing. Plants fully hardy. Establishment time 3-4 weeks. Recommended for those wanting early flowering, or specific varieties that establish well so early in the season. Minimal aftercare (watering) required at this time of the year.
MAR - Great time to plant. Establishment time 2-3 weeks, minimal aftercare (watering) required at this time of the year.
APR - Best time to plant. Establishment time 2 weeks. Keep watered in hot dry weather.
MAY - Great time to plant. Establishment time 10-14 days. Keep watered in hot dry weather.
JUN - Good time to plant if you can be attentive to watering, and weed competition, during establishment (10-14 days).
JUL/AUG - Still possible to plant if you can be attentive to watering, and weed competition, during establishment (10-14 days). Wildflowers are trimmed before sale at this time of the year. You cannot plant big flowering plants, they wilt. Cutting them back stimulates a second flush this year, and more rapid establishment.
SEP - Good time to plant if you can be attentive to watering, and weed competition, during establishment (10-14 days).
OCT - Possibly joint-best time to plant, as your wildflowers can root and develop over the subsequent Autumn and Winter, ready to grow away the following year. Minimal aftercare (watering) is required when in Autumn. It's usually damp which is great for roots. Establishment 2-3 weeks.
NOV - Most varieties can be planted right up to mid November. Indeed, Autumn planting usually gives slightly better first-year flowering from the following Spring.
DEC - Often too cold for good establishment, risk of death in freezing weather in year 1, so not recommended.