Days to germination: 8 to 12 days
Days to harvest: 50 to 60 days
Light requirements: Full sun and partial shade
Water requirements: Constant moisture
Soil: High in organic content
Container: Almost required
Though having some natural water in your yard can help, you don’t actually need a stream to grow watercress. But a large bucket, bin or even a kiddy pool could do the trick. While the plants do need a lot of water, they can still give you a harvest if grown in soil.
Since growing right in a stream is unlikely for most people, these instructions will be for anyone wanting to grow watercress in pots.
Watercress is a perennial that can survive the winters up to zone 5, though dealing with the water-filled containers can be awkward when the weather drops below freezing.
Delicate watercress leaves have a peppery flavor, and are usually eaten fresh and raw in salads or sandwiches. Cress has lots of vitamins A, K and C as well as calcium and iron. It’s a very healthy green. If you use it in cooked dishes, it will be much milder in flavor.
Starting from Seed
You can germinate your seeds indoors, but the fine roots make transplanting difficult. It’s easier to plant your seeds right into their final pots instead.
Before you do any planting, you need to prepare your “water garden” area. You’re going to need a large container for water, and smaller pots that fit inside it for the soil. A small pool is ideal, but a series of buckets can work just fine.
Choose pots that will fit inside the larger container, and fill them with potting soil mixed with some lime. Add extra stones to the bottom to make sure the soil won’t wash away through the drainage holes in the bottom. Now fill the larger container with water, and set the ones with soil inside.
The water level should not be higher than the tops of the inner pots. In fact, the water level can be quite low as long as the bases of the inside pots are always sitting in water. Even just a large tray would work but during the hot and dry months, it won’t likely hold enough water. You would end up having to refill the tray several times a day, which is not exactly ideal.
Set the whole thing up where your plants will get lots of sun, but partial shade during the hot afternoons.
Leave it long enough for the water to soak up through the drainage holes and saturate the soil. Once the soil is good and wet, plant your seeds to a depth of about an inch. The seeds should be spaced around 3 to 4 inches apart. A 12 inch pot can hold about 4 plants.
If you can’t find any watercress seeds, you may be able to start plants from fresh watercress that you get at the supermarket. Put a few sprigs of it in a glass of water, and leave it in a sunny spot. If you are lucky, the cut ends will sprout roots that you can transplant out into the same wet pots as described above.
As long as you never let your plants dry out, there should be little for you to do with your watercress plants until you want to start harvesting. Every 2 or 3 days, empty out the water from your “pond” and add fresh water. If you let the water sit for too long, it will stagnate and your plants will be stunted or even die. They need fresh water constantly.
After the growing season is over, watercress is surprisingly hardy during the winters. They can tolerate being frozen, though letting the water in your pool or bucket freeze can end up splitting the containers. Leave your entire growing set-up in place until you start to get hard freezes each night. Then drain out the larger pool, and leave the actual watercress pots somewhere sheltered.
Until the pots actually freeze for the winter, add extra water each day so they don’t dry out. Once frozen, they should be fine until spring. Once they start to thaw, add more water again until the frosts have passed and you can replace their “pool”.
As mentioned above, since most people do not have streams handy, this article reflects the techniques for growing watercress in containers.
Even if you do have natural water nearby, container growing is cleaner and you don’t have to worry about water-borne diseases contaminating your plants.
Pests and Diseases
Watercress is typically only bothered by 2 main insect pests: flea beetles and mustard beetles. Both of these small beetles can do a lot of damage to your plants by chewing on the leaves.
The easiest way to get rid of them is to dunk your entire pot of watercress underwater for about an hour. It won’t harm the plant (though some soil may wash away if you’re not careful), and the insects will either drown or be washed off the plants.
Some gardeners will plant a few extra radishes nearby to attract these same insects away from your watercress plants.
Harvest and Storage
You can pick the leaves of watercress for use, but make sure you don’t disturb the roots. Use a pair of scissor to cut the leaves and tender stems off, rather than pulling. Wait until the stems are about 6 inches long, then you can snip them off close to the soil level. Never take more than a third of any plant at one time.
Once your plants go to flower, the leaves will quickly lose their lovely flavor and get bitter. So your harvest period usually runs from spring into late summer, depending on your climate.
Watercress does not store for very long once picked. Wrap the pieces in a plastic bag, and keep in the fridge. It will start to wilt after just 2 or 3 days so make sure you do your harvesting right before you intend to you it. Unfortunately, due to the high water content in watercress, it will not freeze well enough for any long-term storage that way.