When lettuce, spinach, and arugula start producing flowers, you can usually consider them done for the season.
Flower stalk formation is known as bolting, and the process changes both the flavor and texture of the leaves. I like to think of bolting as a plant’s last-ditch effort at survival, in the same way that a dying tree will set an extra-heavy seed crop.
Bolting occurs in response to temperature and/or lengthening days. Sometimes this happens very early when we experience above-average temperatures in the region. Temperatures this spring, however, have been mild, and many gardeners would think it to be quite favorable for lettuce and spinach growth.
“I’ve always thought of spinach as seeding in response to heat,” says Dan Nagengast, owner of Seeds from Italy and rural Lawrence resident. Nagengast, and his wife, Lynn Byczynski, grow many of the varieties of the seeds they sell for their own consumption.
Although Nagengast says he got a couple of cuttings from the spinach before it started producing its fuzzy, white flowers, the arugula and lettuce began to bolt after just one cutting. Other gardeners and producers in the area have reported similar experiences.
So what is going on this year?
Like Nagengast, I associated bolting as a response to high temperatures. Turns out that extended periods of cool weather can also cause cool-season crops to bolt. Cool-temperature responses are more often associated with planting too early in the spring, but this year’s mild temperatures are all the same to plants.
Besides the leafy greens, radishes, turnips and mustards are also prone to bolting in extended cool periods. For these crops, the flowers may be enjoyed on salads even though the rest of the vegetable becomes less desirable during flower stalk formation. The flowers have a little spice to them, just as the radishes and turnips if harvested after bolting.
A few other vegetables sometimes bolt: broccoli, cauliflower, kale, and collards produce flower stalks if transplants are mature enough when set out. Biennials like carrots and beets can have their life cycle shortened from two years to one if they experience cold temperatures for an extended period.
I recently talked to a grower whose Brussels sprouts (another biennial) were producing flowers instead of the vegetative growth he hoped for when he planted them extra early.
To prevent cool-season crops from bolting, avoid planting too early or too late in the spring. I wish I could be more definitive, but March and April still provide the general window for spring crops. Cool-season crops can also be planted in the fall with very little chance of bolting.
Once leafy greens and other cool-season crops begin to bolt, you can enjoy their flowers for a few weeks, try the flowers or move them to the compost pile. Maybe the past-prime plants will open up some space for sweet potatoes or another summer crop.