Farmers and their crops sometimes have different goals in mind. Even for highly domesticated crops, the primary biological imperative is still to reproduce, and thus to produce seeds. This is great when the seed is the crop (corn, peas, beans), not a problem when it’s part of the crop (tomatoes, peppers, squash), of no concern when the crop reproduces vegetatively (potatoes, Jerusalem artichokes), but a problem for many leafy or root crops (greens, radishes). When the latter start going to seed, the process is called bolting, and it can radically alter the flavor and.or texture of the edible portion of the plant. Above are four recent photos of leafy crops bolting, from left to right: collards, kale, sorrel, and cilantro. In all four, the bolting process starts with the plant’s central stem becoming elongated, with leaves starting to branch from a rising stalk rather than from a central cluster at ground level; the kale is shown in early stages of this. Eventually the stalk shoots past the lower leaves, as in the collards and cilantro, and puts on flowers, as seen in the sorrel photo, which are then pollinated to produce seeds.This can be very pretty, but agriculturally problematic when bolting occurs ahead of schedule.
Once this process takes hold, the flavor of the leaves tends to become much stronger and generally less edible, and some roots become woody and less appetizing. As a rule of thumb bolting ruins the plant as an edible crop, though we’ve found that sorrel is pretty resistant to negative effects (the leaves from the plant above still taste good), and spinach can be salvaged if harvested promptly at first sign of bolting. Radishes become nastily strong and tough once bolting takes hold, lettuce becomes very bitter, and cilantro loses its appeal. A bolting cilantro plant, if left to flower and set seed, has another culinary life in front of it as coriander (we save our own coriander seed; very tasty). Farmers need to be aware of bolting and the conditions that lead to it, if nothing else to try to salvage a crop before it’s ruined whether or not it’s quite ready.
Crops tend to bolt in response to temperature, though other stresses can lead to bolting as well (root disturbance, for example). Lettuce, radishes, and cilantro will bolt in the season that they’re planted. Other crops, such as beets and carrots, won’t bolt until they’ve been through a significant cold spell (winter); these biennials rarely bolt prematurely and bolting isn’t a problem if they’re harvested in the year they were planted (though their flavor can still be adversely affected by heat). Leafy crops that we overwinter, such as spinach, sorrel, collards, and kale, will often put on a nice flush of spring leafy growth with the increasing sunlight of spring if the temperatures don’t heat up too fast, though the fact that they’ve been though the winter means that they’re biologically ready to set seed when it does warm up. So in a very early, warm spring like that of 2012, bolting is a very real danger even in early March for crops which might normally make it well into April here in Missouri. Bolting can also be triggered by strong warm/cold/warm cycles which trick plants into thinking they’ve gone through a full year of seasons.
The photos above are all of crops we’d overwintered from 2011 with hopes of including in spring CSA distributions, but the rapid warmup has led them all to bolt so quickly that we had little to no meaningful harvest from them. There is little to be done; we’ve spread shade cloth over some of our spinach to possibly forestall this process. So far the spinach is behaving. However, it’s difficult to fight the onslaught of temperatures up to 30 degrees over average this early in the season. In an average spring, we’d probably have gotten at least one good harvest from the crops in the photos.
Bolting is a fact of life in farming, but it’s a good reminder that there are always balances to any given weather conditions. This early spring is helping get many crops off to an early start, but it’s also ruining some existing ones, and may yet cause problems for just-planted crops like radishes which will be extra spicy and potentially bolt more quickly if the heat continues.