What's Parsley? How to Grow It Before It Turns Bitter

Parsley is a hardy biennial, and NC State adds that it is usually grown as an annual.

Wisconsin places it in the carrot family, Apiaceae, alongside carrot, celery and cilantro. Those two facts explain why a parsley plant that returns in spring disappoints.

In its first year the plant does what you want.

Wisconsin gives the rosette of leafy stems as 12 to 18 inches tall, and it keeps producing for as long as you keep cutting. That is the parsley anyone means when they say parsley.

The second year is a different plant. It stretches to 2 or 3 feet and produces greenish-yellow flowers in compound umbels, followed by small ridged seeds.

Illinois is blunt about what happens to the part you eat, saying the leaves become very tough and bitter.

Illinois recommends starting new plants each season for that reason, which makes a parsley bed a yearly sowing rather than a permanent planting.

There is one reason to leave a bolting plant standing. It is still a swallowtail host while the caterpillars are feeding, so a plant the kitchen has finished with can stay useful in the bed.

Two types sit side by side on every herb bench.

Illinois Extension describes moss-curled parsley as finely cut and tightly curled, and names its job as garnish.

Flat-leaf it calls the preferred parsley for cooking, because it has more flavor.

Both are Petroselinum crispum and both are grown in exactly the same way. The choice is about what the leaves are for rather than about how much work either one takes.

Wisconsin adds a second reason to prefer the flat type, saying flat-leaved types may overwinter better than curly leaf types. That only matters if a fall sowing is being carried through, which is covered further down.

If there is only room for one plant, the sources point at flat-leaf.

Curly is worth growing when the look of a plate matters.

The other essential kitchen herbs take the same conditions and sit beside either one.

Most failures with this plant happen before a single leaf shows.

NC State says it is easier to grow from seedlings because the germination period is long.

Wisconsin puts a figure on that, saying seeds may take several weeks to germinate, especially in cool, wet soils.

Both sources reach the same preparation. Illinois suggests soaking the seeds in water overnight before planting because parsley is slow to germinate, and Wisconsin says soaking overnight helps to enhance germination.

Soil warmth matters here. Wisconsin's note that germination is slowest in cool, wet soils is the case against an early outdoor sowing into cold ground.

Illinois suggests that radish trick precisely because radish germinates quickly. The radishes come and go long before the parsley needs the space.

None of this is required. NC State's own advice is that seedlings are easier, and the seed-raising guide covers the longer route for anyone who wants it.

Soil is where this plant asks for more than the woody herbs do, not less. Wisconsin says to place plants in relatively fertile soil, and adds that this is more so than for other herbs, which are usually best in unfertile ground.

NC State lists clay, loam and sand as all tolerated. The pH band is wide, running from acid below 6.0 to neutral between 6.0 and 8.0, and the light requirement is full sun of six or more hours.

Moisture is where it parts company with rosemary and thyme. NC State pairs good drainage with moist, which is a narrower target than either word manages on its own, and it is the pairing rather than either half that a bed has to deliver.

That combination is easiest to hit in a bed with organic matter through it, or in a pot with a mix that drains freely and gets watered often. A dry parsley plant stalls, and a waterlogged one rots.

Spacing is the part most people skip, and the two sources bracket it rather than agreeing exactly. Anywhere from 6 to 12 inches gives a clump wide enough to cut from all season.

Illinois sets the start point loosely, saying parsley can be cut any time after it has become large enough.

Wisconsin gives two methods.

Pinch off sprigs as needed, or cut the entire plant where larger quantities are wanted.

Where you cut matters more than when.

Take whole stems from the outside of the clump, close to the base, and leave the young growth at the center alone. That center is where the next flush comes from.

Picking leaves off the top instead leaves a plant full of bare stalks.

Cutting the whole plant is a real option rather than a last resort, and it is what Wisconsin describes when a larger quantity is wanted, such as a batch for drying.

Storage is unusually forgiving. Wisconsin says both the leaves and the roots retain their flavor when dried, which is not true of most soft herbs, and Illinois adds that potting a plant in the fall for indoor use works if it is discarded in the spring.

Sometimes, and Wisconsin is careful about the word. A fall sowing may sometimes be successfully overwintered for harvest in early spring, which is worth trying where the winter is not severe.

The catch follows from the biennial habit.

A plant that overwinters is already into its second year, and Wisconsin says the leaf flavor is not as good in the second season.

An early crop of mediocre parsley is still earlier than anything sown in spring, so whether that is a good trade depends on what it is for.

Type choice tilts the odds. Wisconsin says flat-leaved types may overwinter better than curly leaf types, which is one more reason to grow the flat one if only one is going in.

A boldly striped caterpillar on parsley is not a pest to be dealt with. Both NC State and Wisconsin list parsley as a larval host plant for the black swallowtail, Papilio polyxenes.

The caterpillar has a common name of its own, the parsleyworm, which NC State lists among parsley's insects. It is green, banded in black and spotted with orange, and nothing else on a parsley plant looks like it.

That changes the decision. A plant can spare a few leaves, and moving the caterpillar to a spare plant costs less than losing the butterfly, which is why parsley turns up on butterfly garden lists.

The insects that actually cost you a crop are far less obvious than the caterpillar. Dill sits in the same family and shares the swallowtail and the aphids, which is worth knowing if the two are grown together.

Two diseases are named across the sources. NC State gives septoria leaf spot and stem rot, and Wisconsin singles out Septoria apiicola as the most common, both of which build up in crowded, wet foliage rather than arriving out of nowhere.

Spacing is the response to most of that list. A plant given its 6 to 12 inches dries between waterings and sees fewer of all of them.

Parsley is toxic to dogs, cats and horses, according to the ASPCA. Its record names furanocoumarins as the toxic principle and photosensitization, meaning sunburn or dermatitis, as the effect, and adds that large amounts are needed to cause it.

Photosensitization is a reaction to sunlight. The furanocoumarins make skin burn more easily in the sun, and NC State does not list contact dermatitis for parsley, so the problem follows eating a large amount rather than brushing past or handling the plant.

In practice the case to avoid is a pot within reach of an animal that grazes it. For a suspected large ingestion, the ASPCA's advice is to call a veterinarian or its Animal Poison Control Center.

A second safety point has nothing to do with the garden plant. Montana State University Extension notes that poison hemlock, which is also called poison parsley, belongs to the same family, and that the most recent human deaths from it came from mistaking it for edible members of the carrot family. Parsley for eating comes from a bed sown or planted on purpose, never from a wild plant that looks like it.