Bolting in overwintered vegetables:
If you’ve ever grown kale, broccoli, cabbage or any of the Brassica genus in your garden, and let them overwinter in a mild climate like our Pacific Northwest climate, you know what bolting looks like.
Northwest gardeners and market farmers often plant a variety of overwintering crops like kale, leeks, chicory, cabbage, chard and maybe even semi-cold hardy crops like lettuce. In an average Pacific Northwest winter, most of these vegetables can produce into December and then come through the winter and produce into the early spring.
Growers of overwintering vegetables, generally plant transplants into the field in August and harvest from late September through December. Things often start tasting better after some light frosts in October/November, but then start getting weird after a few hard freezes. Leaves dry out in kale, lettuce leaves start de-laminating (it looks like the plant equivalent of a peeling sunburn), and most crops pause their growth.
Some winters are harsher than others and damage to plants may be more or less, but either way, plants generally stop growing all together by December. This is due to the lack of enough daylight, as well as the low winter temperatures. Things will then stay relatively dormant (depending on the conditions) until late January or early February.
Sometime in February there is enough sunlight to power the plant’s growth again. Things may not grow much at this point, but if temperatures get above 45-50 degrees, plants will certainly grow.
Unfortunately, as soon as plants begin to growing again, the move into a generative (aka reproductive) state. This means they want to go to seed, bolt, flower, make babies, spread their seed, etc.
This is a slow process, at first. You may not even know the plants are starting to bolt but once the temperatures climb a bit more, and days lengthen, the middle of the plant begins elongating rapidly.
This main stem elongation is why they call it “bolting”. The plant’s natural tendency is to send its central stalk as high as it can, make a flower, attract pollinators with it tall showy flowers, and then spread it’s seed as far and wide as possible, which is made more effective by its greater height.
Nearly all modern overwintering vegetables bolt. However not all species do it at the same time, and not all varieties of each species do it at the same time. In our mild Northwest spring, the first crops start bolting in our unheated greenhouse in early February. By early March, many of the outdoor crops are showing signs of bolting as well. And by the end of April nearly all the crops have flowered.
Food after bolting:
The kale is bolting but that doesn't mean its too late to enjoy it. You can continue to pick leaves off a kale plant even if it has started to bud out, and most other leafy crops too, but once they’ve moved into full flowering and start developing seed, the leaf production pretty much stops.
The flavors of the leaves often intensify, and not always in a positive way. In lettuce, the leaves get downright bitter. With leeks and root crops, you can usually still use them if they haven’t bolted entirely. Once they are developing a flower the root portion is, or will become, very woody.
You can also enjoy the flower sprouts from the kales and their Brassica relatives. These little flower buds, that are generally picked before breaking bloom, are exceptional. This seasonal delight is called “raab” or, may have other names like "kale florets".
These raabs are usually picked to include a decent amount of stem, as it is the tastiest part (think Broccolini or baby broccoli). Once the flowers start to open, the stems get fibrous and it’s no longer enjoyable to eat them.
If the stem snaps easily and cleanly it is most likely still tender. Keep the flowers picked off for a longer harvest period.
Quick raab recipe:
Drizzle with olive oil. Roast in oven like asparagus for 5-10 minutes at 450 degrees. Sprinkle salt to taste. Serve hot.
Another great spring food that is only available from the overwintering grower, are scapes, or whistles. These can be found on your bolted leeks, garlic, shallots or onions.
They are the unopened flower buds and can be snapped or cut from the plant. The actual flower part is usually not eaten, and the stem is considered the edible portion. These are Asparagus-like stalks that are mild in the flavors of whatever the plant they are picked from. Scapes are a nice springtime precursor to the garlic, leeks, or shallot bulbs which mature sometime later in the year.
One other crop that I have to mention is purple sprouting broccoli. It is essentially a crop designed to overwinter and produce really good flower buds in the spring.
Similar to the raab, it gets a little tough once the flowers fully open and start to develop seeds. Keep the flowers picked off for a longer harvest, just like any of it’s Brassica relatives.
So, why do plants bolt?
Most of these plants we’ve been talking about our called biennials. Which basically means, they don’t make seed in the first year.
Biennials need to go through a winter (or any cold period known as vernalization) in order to move from the vegetative stage to the reproductive stage.
Each species may need more or less time to vernalize, but it typically occurs in the range of 38-48 degrees. Sometimes if you plant too early in the spring you can have plants go to seed as well. This is because of the plants exposure to too much cold early in their life cycle.
How to Prevent Bolting:
If I could have a grower superpower, I would make plants not bolt. Until then, here's my advice:
Pick bolt resistant varieties! There are some varieties that are better than others. Some varieties have been bred by plant breeders to bolt later, or not bolt at all.
My Favorite Overwintering Varieties:
I haven’t found any leeks that have proven to be late bolting. This is something someone should be selecting for.
Lettuce and chicories:
All seem to bolt at similar rates, I wouldn’t recommend holding them overwinter at all unless you harvest before January for lettuce, or before March for chicories.
Superstar, January King.
Purple Sprouting Broccoli:
Market Farmer and Gardener. Vida, Oregon.