Most herbs I grow prefer their soil somewhere between moist and well drained. Water Pepper is different.
Persicaria hydropiper is one of those plants that seems almost designed for a part of the garden where other edible plants aren't particularly happy. It likes wet soil, grows quickly, produces edible leaves and seeds, and has a strong peppery flavour that makes it quite different from the usual salad greens and herbs. Despite the name, water pepper isn't an aquatic plant. It likes consistently damp soil rather than having its roots permanently submerged.
It is also an annual, so you can grow it from seed, harvest the leaves through the growing season, allow it to flower and set seed, and start again the following year.
I became interested in water pepper because I like growing unusual edible plants. Sometimes I am looking for something particularly productive and familiar, sometimes something perennial, and sometimes I simply see a plant I haven't grown before and decide I need to find out what it is like. Water pepper was very much one of the latter.
What Is Water Pepper?
Water pepper is Persicaria hydropiper, although you may also find it listed under the older name Polygonum hydropiper. It is also known as smartweed or marshpepper knotweed.
It is an annual member of the Polygonaceae family and is associated with damp habitats, particularly places around waterways.
The plant itself is not especially remarkable to look at. It produces upright green stems and leaves, followed by small light pink to white flowers If you were simply walking past a patch of it, there is a good chance you wouldn't give it much thought.
The flavour is another matter.
The leaves have a strong, hot, peppery taste. The seeds are edible too and can be even more intense. This isn't a mild salad green. A little goes a surprisingly long way. That is probably the first thing I would tell anyone thinking about growing it.
Why Grow Water Pepper?
There are plenty of plants that are easier to find and probably more useful if you need a large quantity of vegetables for common recipes. That isn't really the point.
Water pepper is useful because it is different. For a start, it gives gardeners another edible option for wet ground. Most vegetable growing advice seems to begin with improving drainage. If your garden naturally has a damp patch, you may spend a lot of time trying to find plants that will tolerate it. Water pepper doesn't need convincing. It actually likes these damp places.
The other reason to grow it is the flavour. Water pepper has a proper kick. If you like peppery greens, mustard, horseradish or wasabi, it is an interesting plant to have available. And because it is an annual, you can start it from seed each year rather than having to maintain a permanent plant.
For me, though, there is another reason. I am curious about plants.
I like growing something unusual, watching how it behaves, saving the seed, and then growing it again. A plant doesn't have to be the biggest, most productive vegetable in the garden to be worth growing. Sometimes it is enough that it makes you wonder what will happen next.
How I Found Water Pepper
My first attempts to obtain water pepper were rather less successful than I would have liked. I had been hearing about Persicaria hydropiper for several years. It turns up occasionally in lists of unusual edible plants, but at the time I was looking it wasn't readily available as seed.
Eventually I came across some plants growing naturally beside a river. The plants were growing close to the water but weren't actually submerged. There were several sizeable clumps growing in damp ground beside the river. That immediately told me something useful.
Descriptions of plants can tell you that they like wet soil, but seeing a plant growing naturally tells you rather more. These plants weren't aquatic. They weren't sitting in the river. They were growing in damp ground alongside it.
I took two small cuttings. I was confident about the identification before I took cuttings, because I wasn't interested in experimenting with an unidentified wild plant. I was deliberately conservative about taking material from a wild population. There was no reason to remove a large piece of an established plant when a couple of small cuttings would give me enough material to grow my own. As it turned out, the cuttings were remarkably cooperative.
Growing Water Pepper From Cuttings
Water pepper is very easy to propagate vegetatively. The small cuttings rooted readily, and before long I had plants of my own.
This isn't necessarily something most gardeners will need to do, because growing from seed is a much more accessible way to obtain water pepper. But it did teach me something useful about the plant. It is not difficult to propagate.
A cutting is essentially a clone of the parent plant. If you find an individual plant with characteristics you particularly like, taking cuttings allows you to reproduce that particular plant. Growing from seed is different. Seedlings contain genetic variation, which means they aren't necessarily identical to their parent. For someone simply growing water pepper as a herb, that may not matter very much.
For someone who enjoys saving seed and experimenting with plants, it becomes much more interesting. I was interested in both approaches.
The first plants I grew came from cuttings, but eventually I allowed them to flower and set seed. That turned out to be considerably more interesting.
Does Water Pepper Really Need Wet Soil?
This was something I wanted to find out for myself.
It is easy to read that a plant likes wet conditions and assume that it won't grow anywhere else. My experience was a little more complicated.
The water pepper growing in damp soil was clearly happiest. It grew vigorously and quickly became a substantial plant.
I also took a cutting and planted it in ordinary garden soil where conditions were considerably drier. It survived and grew. It just wasn't as impressive.
The plants in the wetter soil had much more vigorous growth, which wasn't surprising given the habitat where I had originally seen the plant growing.
There is a useful distinction here between a plant tolerating conditions and actually thriving in them. Water pepper seems to appreciate having plenty of water available.
So if you have a damp patch in your garden, a low lying area where moisture tends to linger, or another place where ordinary vegetables struggle because the soil stays wet, this is a plant worth considering. You don't need a pond, and you don't need to submerge it. Think wet soil rather than aquatic plant.
Growing Water Pepper From Seed
For most gardeners, seed is the obvious way to start with water pepper.
It can be sown directly into the garden in spring, at a shallow depth of around 5 mm. Germination can take roughly 10-20 days under suitable conditions.
As always, local conditions matter more than an exact number on a seed packet. Australian gardens vary enormously, so use the recommended sowing season as a guide and pay attention to what your own weather is doing.
The most important thing is moisture. Water pepper isn't a seed I would sow into dry soil and then hope for the best. Keep the seed-raising area consistently moist while the seeds are germinating.
At the same time, I wouldn't interpret "likes wet soil" as "turn the seed bed into a swamp". Seeds need moisture, but they also need oxygen. Permanently saturated seed-raising mix can cause its own problems.
If you already have a naturally damp section of garden, direct sowing makes a lot of sense. Once established, the plants can simply grow where they are needed rather than being transplanted repeatedly.
If your garden soil is very free draining, a container can also work well. Choose a reasonably large pot and a growing medium that holds moisture rather than one designed for drought-tolerant plants.
The basic idea is simple: keep it moist and don't let it dry out.
Growing Water Pepper In A Container
A container is also a useful option if your garden doesn't naturally have wet soil. You can control the moisture much more easily in a pot, and it means you can experiment with water pepper without having to redesign part of the garden.
I generally choose a container large enough to allow the plant to make a reasonable amount of growth and position it somewhere sunny. Smaller pots work and keep water pepper alive, but the plants won’t grow as large.
The combination water pepper seems to appreciate is essentially sunny and wet, rather than sunny and dry.
Don't treat it like a Mediterranean herb. That sounds obvious when you think about where the plant naturally grows, but it is surprisingly easy to put an unfamiliar herb into the same conditions as everything else in the herb garden. Water pepper has different requirements. Give it water.
Harvesting Water Pepper
Water pepper is an annual, and you can harvest the leaves while the plant is actively growing.
I found it easy to pinch out the growing tips to encourage branching. This also makes sense if you are harvesting the leaves regularly. Every time you remove a growing tip, you encourage the plant to produce more side shoots.
There is something satisfying about an edible plant that responds to being picked by producing more growth. You don't need enormous quantities of foliage. This is important because water pepper isn't a plant you are likely to eat by the bowlful. Its flavour is too strong for that. A few leaves can be enough to make a noticeable difference to a dish. If you are trying it for the first time, I would start with a small amount. You can always add more.
What Does Water Pepper Taste Like?
The name gives you a pretty good warning, it tastes hot and peppery. But I don't think that completely describes it. Some people compare the flavour with horseradish or wasabi. I can see why, but I find water pepper distinctive enough that I wouldn't simply describe it as a substitute for either.
There is a sharpness to it, followed by quite a strong almost numbing sensation. I find the flavour difficult to describe accurately, which is probably part of what makes it interesting.
The seeds are even more intense. I tasted some of the seeds from my plants and found them impressively hot. I liked them, but that probably tells you more about my taste in vegetables than it does about the taste of water pepper.
If you prefer mild greens, water pepper may not become your favourite plant. If you enjoy unusual flavours and hot herbs, however, it is worth trying. It is a very different heat to chillies, while difficult to describe it is also difficult to forget.
How To Use Water Pepper
The strong flavour means water pepper is best used in small quantities.
Young leaves can be used fresh, including in salads or as a garnish. The leaves and stems can also be cooked. I think it is most useful as a flavouring rather than as the main ingredient.
You could chop a few young leaves into a salad, use them where you might otherwise use a strongly flavoured herb, or experiment with them in cooked dishes. The young seedlings can also be used as a garnish if you find yourself with too many seedlings.
The seeds are edible too and have an intense peppery flavour. There is a practical problem with using them as a spice, though. You need quite a lot of seeds if you want enough to use regularly in cooking. My plants didn't produce a quantity that made me want to spend hours collecting and processing them for the kitchen.
For seed saving, however, I only need a small amount. That is a much easier target.
Letting Water Pepper Flower
Eventually the plant will stop concentrating on producing leaves and start producing flowers. If you are growing water pepper primarily for leaves, you may want to keep harvesting the growing tips for as long as possible, but you can't put off flowering forever. And why would you? Water pepper is an annual.
It grows, flowers, produces seed and dies. That isn't the plant failing. That is the plant doing exactly what an annual is supposed to do. I allowed some of my plants to flower and produce seed at the end of the season, partly because I wanted to see what would happen and partly because I wanted to have my own seed for another season.
Once the plants had completed their life cycle, I collected some of the seed. I also scatter some into the soil in the original pot and I left it alone to see if it would germinate when the time is right.
Saving Water Pepper Seed
The seed left scattered on the soil spent the colder months outside, experiencing whatever conditions the weather provided. When the weather warmed again, seedlings began appearing. The germination wasn't perfectly even.
Some seedlings appeared earlier than others, which wasn't particularly surprising given that the seed had spent months outdoors. I wasn't deliberately trying to cold-stratify the seed. The seed had simply experienced winter naturally.
This is one of the things I find interesting about saving seed. You sometimes get to observe the complete life cycle of a plant rather than simply following the instructions on a packet.
With the seed I collected and stored inside, I sow the seed in spring. These germinated more evenly, albeit slightly later than the seed left to overwinter in soil.
Growing The Next Generation
There is something satisfying about seeing seedlings emerge from seed you collected yourself. It also makes you look at the plants slightly differently.
When you buy a packet of seed, you tend to think of all the seeds as being essentially the same. Once you have saved seed from your own plants, you start thinking about variation.
Water pepper is open-pollinated, so seed-grown plants have the potential to differ from one another. Most gardeners don't need to do anything with that information. Grow the plants, harvest them and enjoy them.
But if you like experimenting, it opens up possibilities. Perhaps some plants will be more vigorous than others. Perhaps there will be differences in the amount of heat. Perhaps some will perform better in slightly drier conditions. I haven't grown enough water pepper plants to make any useful claims about these things, but I am seeing enough variation among my seedlings to make me wonder what might be possible if I grew a larger population and started selecting for particular characteristics.
This is one of the reasons I enjoy growing unusual plants from seed. There is always the possibility of discovering something slightly different.
Seed Or Cuttings?
Having grown water pepper by both methods, I think there is a place for each.
If you have access to a packet of seed, growing from seed is the obvious choice. It is straightforward and gives you the opportunity to grow plenty of plants from a small packet.
Once you already have an established plant, cuttings can be a quick way of producing more.
There is also an important genetic difference between the two methods. A cutting is essentially a clone of the parent plant. Seedlings are not necessarily identical to their parent.
For a gardener who simply wants some water pepper to eat, that distinction probably isn't particularly important. For someone who enjoys saving seed, selecting plants, or experimenting with unusual vegetables, growing from seed is much more interesting.
I would use cuttings if I wanted to reproduce a particular plant, but I would choose seed if I wanted to see what the next generation produced.
Water Pepper And Other Persicarias
Water pepper is part of a much larger group of plants, and once you start looking at Persicaria, you quickly discover there are quite a few species.
Some are cultivated as edible plants. Some are ornamentals. Some are plants most gardeners know as weeds. Several species can look quite similar, particularly if you aren't familiar with them. This is one reason I was careful about identifying the plants I originally found before eating them.
I wouldn't recommend finding a plant that looks vaguely like water pepper and deciding to taste it. With unfamiliar edible plants, correct identification matters.
Growing from a known source of seed is considerably simpler. You know what you planted, and you can observe the plant through its entire life cycle. That is one of the advantages of growing unusual edible plants deliberately rather than relying on something you happen to find growing in the wild.
A Damp Corner Can Be Productive
One of the things I like most about water pepper is that it makes me think differently about garden conditions.
We tend to divide plants into categories. Plants that like full sun. Plants that like shade. Plants that need good drainage. Plants that tolerate wet soil. Then we try to make our gardens suit the plants.
Sometimes it is easier to do the opposite.
Look at the conditions you already have and find plants that suit them. If you have a damp patch where the soil stays wet, water pepper may be a better choice than trying to grow something that wants a dry, well-drained bed. This is something I have increasingly come to appreciate about unusual vegetables. They don't necessarily need to compete with the familiar crops. They can fill gaps.
A plant that isn't particularly useful in an ordinary vegetable garden can suddenly become very useful when you have an unusual growing condition. Water pepper is a good example.
Is Water Pepper Worth Growing?
I think it is.
Not because it is going to replace all the other vegetables in your garden. It won't.
Water pepper is too strongly flavoured to become an everyday salad green for most people (including myself), and if your garden is dry, there are plenty of plants better suited to your conditions.
But if you like unusual vegetables, it is an interesting plant that is sure to start conversations. If you have wet soil, it becomes even more interesting. It grows quickly, it can be harvested repeatedly, it can be grown from seed, and you can save seed at the end of the season. It is also easy to propagate from cuttings if you already have a plant.
And then there is the flavour. I like plants that give me something I can't easily substitute with another vegetable. Water pepper does that.
Would I Grow Water Pepper Again?
Yes.
The original reason I wanted to grow water pepper was simply curiosity. Once I had grown it, I found there was much more to it than simply having another unusual herb in the garden. It grows very well when given plenty of water. It is easy to propagate. It produces edible leaves with a strong and unusual flavour. It produces edible seed. And because it is an annual, you can save some of that seed and start again.
That last part is probably what interests me most now. I am always curious about what happens when plants are grown from seed over several generations. Even when I'm not deliberately breeding anything, there is something interesting about watching the variation that appears among seedlings.
With water pepper, I have only begun to scratch the surface. For someone looking for an unusual edible plant to grow from seed, particularly someone with a damp corner of the garden, I think it is well worth trying. Just remember that water pepper may like wet feet, but it certainly doesn't have a mild personality.
When eating this for the first time, try to remember - A little water pepper goes a surprisingly long way.
Article by Damien Beaumont
