Duckweed is a tiny flowering plant that is found on the quiet waters of ponds across North America. Though it looks like a carpet atop the water, it is actually made up of thousands of these minuscule plants. These little beauties offer protection to aquatic creatures, plus are a favorite meal for ducks, turtles, koi, goldfish, and other aquatic life. Despite its outdoor habitats, you can try growing duckweed indoors for your fish tank, outdoor pond, or any other purpose you have in mind. All it takes is a bit of knowhow and some water to start growing duckweed indoors.
Duckweed grows best in a clear, plastic tray that’s at least 5 inches deep, though 12 to 14 inches is best to give you more room to work with. It should also be about 18 inches long and 12 inches wide to ensure the duckweed has the space it needs to reproduce. Clean the container with straight water rather than soap and chemicals to avoid leaving any residue on the inside of the container.
You can also grow duckweed right in your aquarium if you like. For this process, you’ll need to cover the outside of it with black contact paper. This helps prevent algae growth which will often outpace the duckweed. Adding a small pump is also a good idea to oxygenate the water, though it is best to use it at its lowest speed to avoid too much movement of the water. Be advised that if you have fish or other aquatic life in the tank, they may eat the duckweed, so if you’re trying to expand your supply, this isn’t the best method.
Common Duckweed isn’t picky about the water used, though it will die in saltwater. It grows best in uncontaminated pond water since it will already have the nutrients needed to feed the duckweed. If you don’t have access to pond water, you can use warm, dechlorinated warm water from a well or a rain barrel.
You can also use chlorinated tap water if you have no other option. Be sure to let it sit overnight to allow the chlorine and other chemicals to evaporate before adding the duckweed to the container. If you’re not using an air pump in the container, you may want to blow air into the water using a drinking straw. Do this every 10 minutes until the water is oxygenated.
Another thing to consider is the pH level of the water you’re using. Duckweed grows best in neutral water, so the pH level should be between 6.0 and 8.0, though 7.0 is best for thriving Duckweed.
No matter what type of water you use, it’s a good idea to add fertilizer to ensure that the Duckweed is getting all the nutrients it needs to survive. A balanced liquid fertilizer is best for Duckweed. This will contain equal parts nitrogen for leafy growth, phosphorus for healthy roots and shoots, and potassium to help with photosynthesis and to promote flowering.
Though there will be instructions included on how to use the fertilizer, these are designed for use in potted plants. For water-based plants like Duckweed, it needs to be diluted. For the best results, dilute the fertilizer you’ve chosen with about 5 times the recommended amount of water before adding it to your container.
Add the Duckweed
Once you have the container and water ready, you can add the duckweed. If you have a nearby pond, you can scoop some out and take it home with you to add it to your tank. Of course, you do need to make sure the water isn’t contaminated to avoid contaminating the container of water you’ve prepared. The Duckweed may not survive in this water, requiring you to start over again.
If it is contaminated, you’ll need to rinse the duckweed in warm water before adding it to your waiting container. You can also disinfect it using potassium permanganate. For this process, pour a teaspoon of the chemical into 12 gallons of water. Gently place the duckweed in the solution, let it sit for half a minute, and then remove it again. This will remove any bacteria and pests that may have come home with the plant.
You can also purchase Duckweed from a plant store in your area. This likely won’t require the cleaning process of the pond Duckweed, which makes it much easier to deal with and speeds up your preparations.
Duckweed is used to growing in brightly lit ponds, which is why it prefers full sun. It can also tolerate low light conditions if necessary but you may not get the growth you’re expecting. A warm, sunny location in your home that will provide it with at least 6 hours of direct light is best.
Duckweed is extremely adaptable and survives in the icy winters of the Northern United States, so it can handle the varying temperatures of the changing seasons in your home. It does have a preferred temperature range, though, so keeping the room temperature between 63 and 79 degrees Fahrenheit will ensure that the Duckweed in your home thrives. Outside of this range it will likely still survive, but you may notice slowed growth.
Duckweed grows extremely quickly, so you do need to prune it regularly to avoid total water coverage and reduce oxygenation. This is especially important if you have other aquatic plants or animals in the tank the Duckweed is located in since this floating plant will also block the sunlight from anything growing below the surface.
To thin out the Duckweed, you can use a small scoop or net to remove some of the tiny flowers from your container. You can then use the removed Duckweed in a few different ways. It can be added to your fish tank for a tasty aquatic treat. It can also be taken outside and placed in an outdoor water feature for a more natural look. You can even use the Duckweed as compost, adding it to your indoor or outdoor plants to provide them with some much-needed nutrients.
When harvesting the Duckweed, don’t take too much of it from the container. Higher concentrations of the plant reduce algae growth, keeping the water cleaner.
Growing Duckweed Indoors
Duckweed is an interesting plant, and growing on top of water is a unique challenge to those of us used to traditional container gardening. If you already have an aquarium it’s a great addition to it, and if not it’s still fun to grow. Let us know if you grow duckweed, and feel free to reach out to us with any questions you might have.