When to Start Seeds for Overwintered Flowers | Guide to Overwintering Flowers

Guide to Overwintering Flowers

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1. Overwintering flowers: an introduction
2. Picking crops to overwinter
3. Timing your seed starting
   • Your target transplant date
   • Seeding Dates
   • Learn More

Planning overwintered plantings can be tricky, and the timing feels backward: for many overwintering varieties you start seed in the middle of the summer harvest rush (July and August in Zones 5a–5b).

Identify Your Target Transplanting Date

A newly planted overwinter flower trial in one of our tunnels, photographed in late October.

In our trials, overwinter flowers go in at about the same time as fall bulbs and garlic, which makes a handy seasonal reminder when planning.

Your location sets the light and temperature you get, so it determines your timeline. Note two seasonal dates for your area: the last day of the year with 10 hours of daylight and typical date of the first hard freeze (below 28°F / -2.2°C), after which nights regularly drop below freezing. Shorter days and falling temperatures work together until plant growth stops.

At roughly 44°N latitude, days drop below 10 hours in early November, so in our Zone 5 trials we aim to transplant overwinter tunnel crops between about October 7 and 15. That gives seedlings around 4 weeks to root in and get established before winter.

To find your transplant window:

1. Look up your last 10-hour day and your average first hard freeze date with an app or website.
2. Count back roughly 4 weeks from the last 10-hour day. That is your transplant window.
3. Compare that window with your hard freeze date. If the window lands several weeks after freezing nights usually begin, move it earlier.