Gadenin日本語Get the appThe second-year flower stem is the whole plan
Parsley is a biennial. In its first season it builds a rosette of leaves and a fat taproot full of stored sugar. It then needs a cold winter to switch state. In its second spring it spends everything it stored on a flower stem two to three feet (60 to 90 cm) tall, sets seed and dies.
So a parsley plant that suddenly throws up a thick, hollow, fast-growing stem in its second spring is not stressed, sick or badly watered. It is doing what a biennial does. No amount of cutting the stem out will turn it back into a leaf plant: the crown has already committed, and any regrowth you get is thin, sparse and strongly bitter.
This single fact explains most of the disappointment gardeners have with parsley. They nurse a good plant through a whole year, feel pleased with themselves in late winter, and then lose it in spring exactly when they expected the reward. The answer is not better care. It is sowing again.
Treat parsley as an annual you happen to be able to over-winter. Sow a fresh batch every year and regard any leaves you take off the second-year plants before they bolt as a bonus.
Cold is the trigger, and young plants can be fooled
The switch from leaf to flower is set off by vernalization: a stretch of weeks at roughly 40 to 50F (4 to 10C). A normal winter does this. The trap is that a cold spell in spring can do it too, if the plant is already big enough to respond.
Parsley becomes sensitive to cold once the stem base is about pencil thickness. A seedling below that size ignores a cold snap. A well-grown transplant that goes out in early spring, sits through two weeks of nights near 40F (4C) and then warms up will often bolt in early summer, in what should have been its first productive season. That is premature bolting, and it is entirely avoidable.
The other common cause is a late-summer sowing that grew too fast. Plants that reach a good size before winter arrive at spring large and fully vernalized, and bolt in early spring rather than giving you the long spring picking you wanted. Sowing that batch a few weeks later, so the plants go into winter small, buys you months of extra leaf.
How to avoid losing a season to bolting
Nothing here stops a genuine second-year plant flowering, and nothing should. The aim is to make sure you always have plants at the right stage, and that none of them bolts before its time.
- Wait for settled warmth before planting out Plant out or direct sow once nights are reliably above 45F (7C). Gaining two weeks in spring is not worth risking a plant that bolts in early summer.
- Sow twice a year, every year One sowing in spring for summer and autumn picking, one in late summer for winter and early spring. Overlapping batches mean a bolting plant never leaves you without parsley.
- Keep the late-summer batch small going into winter Aim for plants with four to six true leaves at the first frost, not full-size rosettes. Small plants come through winter and then grow rather than flower.
- Row cover a cold snap, do not fight it later If a hard week is forecast over young spring plants, cover them. Ten minutes of row cover is the whole cure; once the plant has been vernalized there is no undoing it.
- Keep the plants growing steadily Drought, then rain, then drought again pushes any stressed plant toward flowering earlier. Even watering and a nitrogen-leaning feed keep the rosette in leaf mode.
What to do once a plant has bolted
The leaves on a bolting plant turn coarse and noticeably bitter within a week or two, and the plant stops making usable new ones. There is no point keeping it in the bed for the leaves, but there are two good reasons to keep it a little longer.
| Option | What you do | What you get |
|---|---|---|
| Pull it now | Lift the whole plant, root and all, and re-sow the space | Room for the next batch, and no bitter leaves tempting you |
| Let it flower | Leave the umbels for three to four weeks | Flat white-green flowers that hoverflies, lacewings and parasitic wasps work heavily |
| Save the seed | Cut whole heads once the seed has gone tan and dry, and finish drying indoors | Plenty of seed, though it is short-lived and worth using within two years |
| Use the stems | Cut the young stalks before the flowers open | Strong stock and soup flavoring, where bitterness does not matter |
Parsley crosses readily and self-sows freely once you let a plant seed. Volunteer seedlings the following spring are useful, but pull the ones sitting in last year's row so the three-year rotation still means something.
Flat leaf and curled bolt the same way
There is no meaningful difference in bolting behavior between the flat-leaved and curled sorts. Both are biennial, both respond to the same cold trigger, and both go bitter once the stem rises. Flat-leaved types tend to grow taller and produce a more obvious stem earlier, so bolting is simply easier to spot in them, while a curled plant can be halfway to flowering before the change is visible in the middle of the rosette.
The one practical difference is in the warning sign. On curled parsley, watch for new leaves emerging with longer stalks and flatter, less crinkled blades. That flattening of the newest growth is the plant changing state, and it usually shows a week or two before the stem itself is obvious.
The dates that make next year easier
Write down the date each batch bolts, and next to it the date that batch was sown. Two seasons of those pairs tell you precisely how late you have to make the summer sowing in your climate to get an unbolted spring crop, which is knowledge no general guide can give you.
It is also worth noting any spring cold snap after planting out, with the low temperature if you have it. When a batch bolts early in what should be its first summer, that note is almost always the explanation, and it stops you blaming the seed or the soil.