My attempts at growing lettuce this fall have been total failures.
Recommended DC fall planting dates for lettuce are mid-August through the end of September. Lettuce is a cool-season annual, taking about 30-45 days to mature, depending on the variety. So counting backwards from our average first frost date of November 3 (according to the most recent calculations), it's all good...at least, in theory.
The trouble is that lettuce prefers temperatures below 80F.
Washington, DC is a heat island: paved areas experience significantly hotter temperatures than the greenery of parks. Here is an excerpt from the linked Washington Post article above:
“In D.C., we were surprised by the clear boundary between green spaces and developed areas,” Vivek Shandas, a Portland State University professor who led the temperature collection effort and processed and mapped the data for NOAA, said in an email. “The National Arboretum and areas of Ivy City and Brentwood contain a difference of 10F within just a few city blocks.”
...and Carver/Langston, the sweltering NE neighborhood where I live that's just to the south of the Arboretum's oasis. It's no wonder that my first sowing of lettuce seeds on September 20 entirely failed...as did my second sowing, two weeks later on October 4. It has been another two weeks, so I am trying again for the third time on October 18.
Nope, this is not my lettuce. This lettuce is growing at Pomegranate Alley Community Garden in SE DC, which must have a cooler microclimate than in my garden. I'm only slightly jealous. Meanwhile, there's not much to see in my garden at the moment, but hopefully I will have something to show in a few more weeks.
It bothers me that parts of my garden have been unproductive for a month. I've been thinking a lot about Resilient Urban Gardening in the Time of Climate Change (that's my to-be-written book title, don't take it). I feel like I could have made a better choice instead of wasting space and time on lettuce that wasn't going to grow anyway.
Watching the kale and collards thrive in my garden all summer has gotten me thinking about the resilience of biennials. These are plants that tolerate a wider range of temperatures, surviving both the heat of summer and the cold of winter in their preferred climate. It's the "preferred climate" part that's the key, of course. For instance, only in Southern gardens could you expect to overwinter cauliflower, as it is killed by freezing temperatures.
But you know what? I think that's ok. Maybe I have space in my fall 2019 garden for veggies like cauliflower after all. They don't survive a hard freeze (less than 30F), but they do fine with fall nighttime lows of 40F to 50F. Meanwhile, they also survive the higher than 80F temperatures that we should probably come to expect in September and early October in DC. With some careful planning, I can plant a succession. Fall-only veggies can be interplanted with winter-hardy veggies. That way, after the fall-onlys are harvested and eaten, the winter-hardys will have more space to grow and mature.
In order to make this work next year, I will choose fall-only varieties that mature in 60 days or less. That way, late-August or early-September planted veggies will have enough time to mature to a harvestable size before the November 3 average first frost date. This could include 'Early Snowball' cauliflower, 'Green Goliath' broccoli, 'Ryokuho' Chinese broccoli, and 'Early Green' yu choy sum. Next fall, I will interplant these fall-onlys with cold-hardys like kale, collards, Chinese mustard, rutabagas, turnips, tatsoi, leeks, and perennial arugula for a resilient and abundantly-productive garden.
As for the lettuce, I'll save it for the early spring, as that's when my past experience has shown it to be the most successful anyway.