Young turnip and radish plants.
Credit Kathryn Simmons
We’re in cold-hardiness zone 7, and our average first frost date of October 14. This makes the first half of August our last chance to sow several vegetables and get crops from them before winter. In 2012 I wrote Last Chance Sowings. Depending on your climate zone, your dates might need to be earlier or later than ours. Fall vegetable growing provides fresh harvests, storage crops and possibly some crops to overwinter.
There are three categories of vegetable crops to consider planting at this time of year:
- Warm weather crops that die with frost.
- Cool weather crops that grow well in spring and fall, but don’t thrive in the summer.
- Cold-hardy crops to grow over winter and get off to a fast start in early spring.
Planning and timing are crucial – if germination fails, you may not get a second chance with that vegetable. The twin challenges of fall crops are sowing in hot weather, followed by keeping the crop happy in cold weather.
Warm weather crops
Don’t stop too soon! But don’t plant too late to have a reasonable chance of success. For crops to be harvested before killing frosts arrive, the formula to find the last sowing date for frost-tender crops is:
Number of days from outdoor planting to harvest (read the seed packet or catalog)
+ Number of days from seed to transplant if growing your own starts
+ Average number of days of harvest period
+ 14 days “Fall Factor” to allow for the slowing rate of growth as the weather cools
+ 14 days from your average first fall frost date (in case of an early frost)
= Days to count back from your average first fall frost date
For example, yellow squash takes 50 days from sowing to harvest, and our last planting is 8/5, a whole month later than we could risk without rowcover to throw over on chilly nights. Don’t worry that rowcover prevents pollination – you don’t need to get every flower pollinated, just keep the developing fruits growing. In many parts of the country, a frost or two will be followed by a few more weeks of warm weather, so getting past the first few frosts is worth the effort. (Unless you’ve reached the exhaustion point we call “Praying for a Killing Frost.”) It’s easy to get harvests for an extra month from mature plants you already have.
Cool weather spring and fall crops
Beets, carrots, chard, spinach, lettuce, scallions, peas, potatoes, Asian greens and other leafy brassicas, turnips, rutabagas and radishes all fall in this group. Fall gives you a second chance to enjoy these crops. The flavor of crops produced during warm sunny days and cool nights can be a delightful combination of sweetness and crunchy succulence.
We sowed 60% of our fall carrots last week, along with some “indicator beets,” and I ran overhead irrigation Wednesday, Thursday and Friday nights, on a third of the length each time. The indicator beets started to germinate on Sunday, and so yesterday (Monday) we flame-weeded the beds. Last night we got a little rain. Today there are hazy rows of green – germinated carrots! Maybe you’re wondering why we only sowed 60% of what we wanted. Well, we ran out of seed! Embarrassing and annoying, but oh well. More is on order, and it’s not too late to sow them, although they have less time to grow big. Every day counts in the fall!
The formula for calculating last sowing dates for frost-tender crops can be modified for hardier vegetables. For example, Early White Vienna Kohlrabi takes 58 days from sowing to harvest (line 1). You can direct sow, so line 2 = 0. You can harvest it all at once and store it in your cooler, so line 3 is 1 day. Assuming you don’t want to use rowcover for this, line 4 = 14. Line 5 = 14 also. That all adds up to 87 days. Kohlrabi is hardy to maybe 15°F. The temperature is not likely to drop to 15°F before the beginning of November here, so counting back 31 days in October, plus 30 in September, plus 31 in August – that’s 92 days already, more than enough. We could sow kohlrabi in early August and get a crop at the end of October.
We have made ourselves a chart for fall harvest crops so that we don’t have to calculate each time. It helps us ensure we don’t sow too late to get a decent harvest.
Sowing dates for crops with various days to maturity
We’ve sown two beds of beets, one of kale, some winter radish and fall radish. We’re behind on tilling and prepping beds, or we would have more. We’re experiencing the domino effect of getting late with one task, and then struggling to catch up as more and more tasks get behind-hand. We were late with our potato harvest. And therefore with our broccoli and cabbage transplanting (which uses that plot). Because we are transplanting older plants, we’re removing a couple of the older leaves from each one as we plant, to reduce transpiration losses. We’re late with tilling and bed prep, and therefore with planting. But we do still have hope. One of our mantras (learned from another farm) is “Prioritize planting during the planting season.” Here the planting season extends from early February to November outdoors.
We don’t sow spinach till September, so we’re not behind on that yet! Because spinach germinates so poorly in warm soil, we wait for temperatures to drop. This “summer” has been extremely cool, but we’re in no hurry to start spinach earlier than usual, because of all the other tasks. This year it would probably work. I saw fall dead nettle germinating on 8/4. That’s a phenology sign that the soil is cool enough for spinach.
I’ve been recording phenology data here since 2003. 8/4 is the earliest date I have for dead nettle, by a margin of 11 days! It has been as late as 9/1 (2004).
Cold-hardy crops to grow over winter
I covered this topic in detail in Growing for Market in September 2010, and in my slideshow Cold-hardy winter vegetables. The gist is “Before taking the plunge, know your climate, know your resources, know your market, know your crops, and when you don’t know, experiment on a small scale.” Useful information includes the winter-kill temperature of your desired crop. Choose hardy varieties, and be clear about whether you intend to harvest outdoors all winter (kale, spinach, leeks, parsnips, collards for us), or whether you want to have small crops going into winter so you can rest during the winter and be first out the gate in early spring, with crops waiting for you.