Water Lettuce: a Low Maintenance Floating Plant

 This gardening post will be a different because we’re going soilless and into the water! This is the water lettuce, your quintessential pond plant.

The pistia is also known as water cabbage, water lettuce, nile cabbage, or shell flower. It is a plant that floats freely on the surface of the water, but unlike lily pads that grow flat with the surface, these grow rosettes above the surface. These grow as a beautiful lush green radial, that can grow quite big (leaves grow 2-15 cms). Beneath is a bushy root system akin to thin hairs: perfect to take in nutrients from the water. This is a warning right at the beginning that this is considered an invasive species in many places due to how quickly it reproduces.

Low maintenance

As with all water plants, you just need to make sure that you put it in water. Water lettuce grows best in bright direct light. What this means is you have to choose a good place to put your tub or pond, and you’re set. In my case, I have it in a 5 inch deep plastic container, and the only maintenance I do for the plants is making sure to refill the water. A single plant will grow big if there are enough nutrients in the water (you can put in a hardy fish to provide that organic matter). To compare this with other plants, you never run the risk of root rot or overwatering.

Multiplies like crazy

The distinguishing characteristic of water lettuce is its ability to multiply. It does so asexually: from a mother plant, you’ll see a stem extending out, from which another rosette will start to form. One key thing about water lettuce is that as opposed to submerged plants, the leaves, in other words the sites for photosynthesis, are above water. Physics tells us that the intensity of light diminishes as you go further down the surface, which is sometimes why submerged plants can be slow growers. Water lettuce can get all the sun it wants, and this makes it grow like crazy. 

To tackle how it is an invasive species, all you actually need is one plant, and you can expect that it will cover every surface of your pond or tub after some time. Lilies for example, are constrained by its root system, planted in soil at the bottom of your pond. The water lettuce has no such restrictions. With a good source of nutrients, it spreads even quicker. To be fair, it’s very easy to just take them out (they’re used as fertilizer and at times as feeds), but you can expect that if you’ve left at least one, it will seek to cover the surface again.

It is a really good water filter

In general, any fast growing plant will be a great filter (see the pothos for example). The water lettuce is no exceptions. It’s root system is thick, and when it’s at its maximum size, it will continue to take nutrients to both maintain itself and to multiply. You can expect that it will take in most minerals in your water.

Great and destructive addition to ponds and aquariums

Given all this about the water lettuce, it can be both very good and very bad for your ponds and aquariums. Really quickly, indoor aquariums will need a bright light. In any case, it can do good for fish because it is a great water filter (taking out nitrates that are toxic to fish). Second, it provides a great hiding place for fish. You’ll see fish will be less stressed with submerged plants, and in this case the root system is plenty for small fish (hence how it is great if for the reproduction of some fish). My betta loves resting in its roots. Lastly, as a floating plant, it blocks the sunlight and is absolutely amazing and killing at preventing algal blooms.

And these same characteristics can make it really bad for aquariums and ponds. Its prevention of algal blooms also means that it is bad when you mean to put submerged plants. Submerged plants will get no light. Lastly, because water lettuce will want to cover the surface of your pond or aquarium, it actually decreases the interface between water and air, effectively reducing oxygen that your fish may need. Hobbyists will often cordon off part of the water surface with a net to keep it clear of these plants.

What It’s Not

First the obvious that this is not a terrestrial plant, and that it’s an aquatic plant. Second, this is not a  submerged aquatic plant: it will not root at the bottom (note how I don’t even need a really deep tub to grow these). This is not a plant that is constrained by a root system in one part of the bottom of the plant: it will seek to cover the whole surface of your pond. As a guide to the other aquatic plants, note fully submerged ones, and those that are emergent (those that have root systems in the soil at the bottom that shoot leaves emerging out of the water).


■■■□ A great beginning plant that falls short of perfect due to how it can be invasive

For the most part this is an idiot-proof plant that will just keep on multiplying. I find the lush green almost like a water lawn: it can be quite beautiful. Just note the obligatory warning that it can be invasive.

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