How to Plant Water Dropwort (Water Celery) in Wet Ground

Start from a bought plant, never from a wild one

Before anything else: this plant has close relatives that are among the most poisonous things growing in the temperate world. Hemlock water dropwort and its cousins live in exactly the same ditches and stream margins, carry the same divided parsley-like leaves and the same flat white flower heads, and a mouthful of the root has killed adults. There is no reliable field test a home grower can apply, and the confident-looking identification guides on the internet do not change that.

So the rule is absolute and it is the same rule commercial growers work to. You start from a plant or a seed packet bought from a nursery or seed company that sells it as an edible crop, you keep it in a bed or a pot you planted yourself, and you never harvest a leaf from a wild stand no matter how certain you feel. Everything else in this guide assumes you have done that.

If you inherit an unlabelled patch of divided-leaved greenery in a wet corner of a new garden, treat it as ornamental, not edible. Grow your own from a bought plant alongside it and eat only from the one you planted.

What the plant actually wants

Water dropwort is a marginal aquatic perennial. In the wild it grows at the edge of slow water with its crown at or just above the waterline and its roots permanently saturated, and that is the condition you are trying to copy. It does not want a well-drained vegetable bed that you water often; it wants ground that never dries, or an inch or two (3 to 5 cm) of standing water over the soil.

It takes full sun where summers are cool and the roots stay wet, but in hot regions it does better with sun in the morning and shade from mid afternoon. Leaves grown in hard sun with warm roots turn tough and strongly flavored; leaves grown in half shade with cold wet roots stay tender. It is hardy well into cold winters as a root and crown, and in mild regions it keeps producing leaf right through the cold months.

Decide the boundary before you plant

This plant spreads by stolons, horizontal stems that run out across the surface of wet mud and root at every node. One small plant covers a square yard in a season and keeps going. That is exactly what you want in a crop you cut every few weeks, and exactly what you do not want loose in a pond margin or a wet ditch that connects to open water. In several regions it is treated as an invasive wetland plant, so check what your local authority says before planting it in ground that drains to a natural watercourse.

The practical answer is a container of some kind, even in the ground: a bottomless bucket sunk to its rim, a pond basket, an old washing-up bowl with a couple of holes punched high on the side, or a bed edged with buried boards standing 4 inches (10 cm) proud of the soil. Stolons run over the surface rather than diving deep, so a low physical rim stops them where a buried barrier alone would not.

1. Pick the wettest spot you have The low corner that stays muddy after rain, the ground below an overflow, the shady side of a water butt. If nothing on your plot stays wet, plan on a pot standing in a tray instead of an open bed.
2. Sink a container or edge the bed A 12 inch (30 cm) bottomless bucket, a pond basket, or boards standing 4 inches (10 cm) above soil level. The rim is what stops the stolons, so it must sit proud of the surface, not flush with it.
3. Enrich and firm the soil Fork a couple of inches of well rotted compost or manure into the top 8 inches (20 cm), then tread it firm. Loose fluffy soil floats and slumps once it is flooded; firm heavy soil holds the stolons down where they can root.
4. Flood it and let it settle for a day Fill the area until water stands on the surface, leave it overnight, then top up. Planting into already saturated soil means the crowns never experience a dry hour.

Setting the plants in

Plant with the crown level with the soil surface or a fraction above it, never buried. A buried crown sitting under standing water rots at the collar in warm weather. Space plants about 8 inches (20 cm) apart in a container and 12 inches (30 cm) apart in an open wet bed; they will close the gaps within six to eight weeks and you are better off with a few strong plants than a crowded row.

Any length of stem with a node also works as a starting plant. Push the node into wet mud, weight it with a pebble so it cannot float away, and it will root in a week or two in warm weather. If you were given a bunch of rooted stems rather than a potted plant, this is the way to establish them: lay them flat, peg them down, and let them root along their length rather than trying to plant them upright.

1. Set the crown at surface level Make a shallow depression, spread the roots into it, and firm soil around them so the growing point sits just clear of the mud. Water covering the leaves for a few hours does no harm; water permanently covering the crown in summer does.
2. Peg down any loose stems Lay stems flat along the wet surface and hold each node down with a stone or a bent wire staple. Every pegged node becomes a separate plant.
3. Cut the plant back by half after planting Removing half the top growth at planting stops the plant losing water it cannot yet take up and pushes it into producing new shoots from the base. You lose two weeks and gain a much denser plant.
4. Keep the water topped up for the first month Check every second day in warm weather. Establishment is the only period when a dry day can actually kill a plant rather than just check it.

The first six weeks, and what to write down

Expect very little visible growth for the first fortnight, then a sudden change as the first stolons appear and start running. Do not harvest anything until stolons are running and the clump has thickened, which is usually six to eight weeks from planting in warm weather and longer in cool. Cutting before then leaves you with a thin patch that takes the rest of the season to recover.

Write down four things now, while they are easy: the date you planted, the source the plant came from, exactly where each plant went, and the date you first saw stolons running. The source matters most, because a year from now you want to be able to say without hesitation which patch is the one you bought and planted. The stolon date tells you next spring how long the plant needs before it will carry a first cut.

Label the planting permanently, not with a plastic tag that fades in a season. A patch of this plant that nobody can positively account for is a patch nobody should eat from.