Is It Too Late to Plant Fall Greens? How to Find Your Last Sowing Date

When is it too late to plant fall greens? In most US zones, your greens need to reach near-harvest size before the days drop below about 10 hours of light. To find your date, count back from your first frost using the days to maturity on the seed packet. A cold frame or row cover buys you some extra time in the cold, but no extra daylight.

I learned this the slow way. One October I sowed a whole bed of spinach right on time by the frost date, and it sat there the size of a thumbnail until March.

The real deadline is daylightcount back from your frost date

A gardener on Reddit put it plainly: "Plants respond to the shortening days." Extension services agree. Nebraska Extension says plant growth largely ceases once daylight falls below 10 hours a day, and Illinois Extension notes that even greenhouse crops grow very little in that stretch without added light. Growers call it the Persephone period, a term Johnny's Selected Seeds credits to Eliot Coleman. Cold slows your greens down, and short days stop them.

You can look up the date your town drops under 10 hours on the U.S. Naval Observatory daylight table. In Lincoln, Nebraska, it runs from about November 11 to January 31. Near Chicago it starts around November 9. N.C. State Extension suggests overwintering crops reach at least 75% of maturity by then.

How to work out your last sowing date

Count backward from your first frost date:

1. Start with the days to maturity on the seed packet.
2. Add 10 to 14 days for what Nebraska Extension calls the "fall factor," because plants grow slower in shorter, cooler days. Add another 10 to 14 days as a cushion if the crop is frost-sensitive.
3. Count that many days back from your first frost date.

If that date already passed, switch to a faster crop or sow under cover.

Finding your frost dateunder 10 hours, growth stops

I took my zone-by-zone table out of this post. USDA hardiness zones map winter lows, not frost dates, and I couldn't find a primary source that ties the two together closely enough to print. Your frost date depends on your town. Your county extension office or your local National Weather Service office publishes average first frost dates from weather station records. Use that date in the count above.

Fastest greens for a late start

• Mizuna and arugula grow fast. Check the packet, but they are among the quickest greens I sow.
• Mache handles cold better than almost anything I grow.
• Spinach sown late often overwinters and takes off in early spring.
• Lettuce works if you pick a cold-tolerant variety.
• Microgreens grow on a windowsill any month of the year.

Sowing late under cover

A cold frame or low tunnel keeps the soil warmer, so seeds sprout later into fall. It won't add daylight, though. Anything you sow late under cover grows slowly until the days lengthen again. I go deeper on this in Will a Cold Frame Work in Zone 6 or 7?.

Overwintering for an early spring harvest

Some of my best spinach comes from seed I sowed too late. The plants sit small all winter, then grow fast in late February. If you missed your window, sow anyway and treat it as your spring crop. My succession sowing plan shows how I spread sowings out.

Frequently asked questions

Can I still plant spinach in November?

Yes, but if your days already run under 10 hours it will likely stay small until spring. Sow it under a cold frame for protection, or treat it as an early spring crop.

What grows in a cold frame if I sow it now?

Spinach, mache, mizuna and arugula are your best bets. Expect slow growth until the days lengthen.

What is the Persephone period?

It is the stretch of winter when days run shorter than about 10 hours and most plants stop growing.

Do microgreens count as a winter crop?

They do for your kitchen. You grow them indoors on a windowsill or under a light, so the season doesn't matter.

Grow what you eat. Keep what you grow.