When to plant wildflower seeds largely depends on the climate and rainfall patterns in your area as well as the type of seeds you are planting. In cool climates, planting wildflower seeds in spring or early summer is ideal since temperatures are warm enough for germination but not so hot that it’s difficult to keep seeded areas moist. Planting in summer is not recommended since it is difficult to keep seed beds continually moist for the first 4-6 weeks. The hot summer sun tends to dry the soil out too quickly.
Wildflower seeds can also be planted in fall in cool climates. Dormant fall wildflower plantings should be late enough so that seeds do not germinate until spring. These must be done when air and soil temperatures are too low for germination, typically after several freezes but before there is snow cover. The seeds will lie “dormant” in the soil until spring when warmer temperatures and moisture are available. Soil expansion and contraction during the winter can also improve seed-soil contact. Perennials can also be sown in early fall provided that there are at least 10-12 weeks of growing time before the plants go dormant for the winter. This amount of time generally allows enough root growth for plants to survive the winter.
Planting wildflower seeds in the fall is a fairly common practice in many regions of the U.S. It is appropriate in the following situations:
- When supplemental irrigation is not available but adequate rainfall is anticipated in the spring. This method works best when springtime precipitation is regular and consistent.
- When it is difficult to prepare soil in the springtime. For these areas, soil preparation, weed control, and seeding can be done whenever the soil is dry enough to work in fall. Many areas in the eastern U.S. tend to have wet springs, and fall site preparation and seeding can be advantageous there.
- Fall seeding can be the best time for seeding in milder climates where spring can be hot and dry. Seeding is typically done early to mid-fall when adequate rainfall is expected. This allows plants to grow large enough to overwinter. In very mild climates, winter is also a second growing season for flowers that prefer cooler weather.
- When wildflower seeds with high dormancy are being sown in cooler climates.
The presence of dormancy in wildflower seeds makes it difficult to get immediate germination when sown in spring, and the winterizing effects of freezing and thawing will help to break the dormancy in the seeds. Seed dormancy is the inability of viable seeds to germinate under favorable conditions. Seed dormancy is an evolved trait that allows a plant species to hedge its bets – it allows some seeds to survive conditions and seasons that are unfavorable for seedling growth. For instance, some seeds may germinate right away but will perish if there is a drought that season. The dormant seeds will be preserved for another season that hopefully will have more favorable growing conditions.