Why Water Lettuce Turns Yellow and What to Do About It


A friend and I went to visit a water garden the other day. Everything looked great, except for the water lettuce, which seemed to have turned yellow and were looking rather sickly. Since I was also planning on planting water lettuce, I thought of doing some research to find out why and how this could happen, and how to fix it.

Why does water lettuce turn yellow and what can one do about it? Water lettuce can turn yellow and subsequently rot if there is a lack of nutrients for the plant in the pond/ garden, or due to excess sun. Yellowing can be fixed by taking out the plants and letting them soak in a fertilizer solution.

Water lettuce is generally an easy enough plant to grow, and is hence almost always a part of every aquatic garden or pond, and is even at home in aquariums if grown properly. Water lettuce can grow prolifically, almost like a weed, in outdoor gardens and ponds, if allowed to overrun, and can choke the rest of the plants in the pond. When cared for and moderated properly, water lettuce can make a lovely addition to the home pond or garden, and is known to provide shelter to any small fish in the pond.

However, water lettuce can also turn yellow due to a few factors and this can lead to it decaying and causing harm to the rest of the garden too. In most cases, the lettuce just yellows and may not affect the life of the plant or the health of the pond, but will definitely ruin the beauty of the garden. Thankfully, the situation is not beyond solutions and can be rectified with time and appropriate care.

Benefits of water lettuce

Water lettuce is actually considered a weed in many parts of the world, and growth of the same is not encouraged in these places. In natural lakes, canals and waterways, water lettuce has often overpopulated and created obstruction of passage, hindering boats and other water transport. However, that does not mean the plant has no uses and is not aesthetically pleasing. Here are some benefits of water lettuce in the backyard pond, before we move on to discussing why water lettuce turns yellow and what can be done-

  • Water lettuce controls the spread of algae in the water. Algae are generally a common problem for those with backyard ponds or water gardens, and most times one has to resort to pumps and aerators to try and fix it. Water lettuce is an excellent addition to the pond for removal of algae and control of algal bloom.
  • Water lettuce has a tendency of absorbing nutrients from the water it is growing in. While this also means that the other plants will need to be fertilized and grown with additional care, the positive of this is that excess nutrients are taken in by the water lettuce, and a balance is maintained in the pond ecosystem.
  • Water lettuce roots and leaves are an attractive and safe home for frogs and small fish that may live in the pond. The leaves provide shelter to these creatures, and the roots are a great spawning ground.
  • Water lettuce is also rather pleasing to look at when it is maintained well and trimmed regularly. The green foliage and the wide leaves of water lettuce provide great aesthetic value to the pond or garden, and are a treat for the beholder.
  • This plant is also a decent oxygenator. While ideally anyone with a home pond or water garden would have an aerator fixed for oxygenating, a little natural help is never amiss, and water lettuce provides just that.

Causes for yellowing of water lettuce and possible solutions

Water lettuce, particularly the variety grown in a pond or outdoors garden, demonstrates growth and health subject to certain conditions, be it weather or the presence of fish in the pond. Here are a few reasons because of which water lettuce might be turning yellow-

  • One of the major reasons for water lettuce turning yellow is too much exposure to sunlight, or harsh sunlight. While water lettuce generally needs warmth and a bit of sun to grow well, too much or too harsh sunlight can scorch the leaves, take away the moisture and turn the lettuce yellow.

If your water garden or pond is under direct and harsh sunlight, consider providing shade in the form of taller floating plants like lilies. Moving the pond or garden might be a rather extreme step and may need a lot of time, so the alternative is to move the water lettuce plants away from the brighter sunlight and towards cooler parts of the pond.

  • Strong artificial lighting can also be a reason for lettuce turning yellow, if not getting completely scorched. As natural sunlight may not always be available for home water gardens and ponds, many people prefer to provide the garden with artificial light. However, sometimes this light may be too intense and can harm the water lettuce if exposed for too long.

It is a good idea to use LED lights if you want to use artificial lighting for your water lettuce, as this type of lighting is not likely to generate excess heat. Try a combination of lighting, especially if your water lettuce is being grown indoors.

  • Another reason water lettuce turns yellow is because the plant is lacking nutrients. In such a situation, the leaves can turn yellow, and although there may not be a massive impact on the plant’s health, lacking nutrients is not an ideal growth condition and should hence be addressed swiftly. One can tell if the water lettuce is yellowing due to lack of nutrition, if no prior nutrient tablets and supplements were being added to the substrate of the lettuce.

If the water lettuce plants are few in number or are small, you can just take them out of their pond or garden gently, and repot them temporarily in nutrient mixes such as liquid fertilizer and Miracle Grow. Only leave the water lettuce in the liquid fertilizer container for a few hours at a time, to avoid overdosing the plants, and do not fill the container to the brim.

If there are too many water lettuce plants to remove, you can go ahead and use a solution of potash in the entire pond or water garden to release nutrients into the water. Nutrients and fertilizers are also available in tablet form and can be easily administered to the water lettuce to restore its color and health.

  • Water lettuce has a tendency of spreading all over the pond or water surface and in the process, the various leaves and parts of the plant can suffocate other parts of the same by creating blockage. Thus, the blocked leaves can turn yellow and may even decay to some extent.

One solution to this is to simply weed out a few water lettuce leaves and perhaps an entire plant every couple of weeks. Weeding out the yellow parts will not only clean up the look of the pond, it will also prevent the growth of excess water lettuce and hence avoids clogging.

  • Water lettuce is a plant that grows well in warm climate. Water lettuce yellowing and often shriveling can be a direct result of incoming winter season and/or frost. While water lettuce is a considerably hardy plant that is actually sometimes hard to get rid of, frost and cold are weather conditions it cannot withstand by itself. Thus the leaves can turn yellow and the plant can wilt.

To protect the water lettuce from cold weather, what one can do is overwinter the plant before the first frost sets in, place it in a sunny area with water temperature no less than 10°C. Water lettuce must be removed from the pond of water garden as soon as temperature drops below 10 °C as then the plant will yellow and may die.

  • Sometimes, the reason for water lettuce turning yellow is the activity of the fish in the pond. Koi fish in particular, tend to nibble at the roots of the plant, which aren’t very strong to begin with. As the roots grow frayed, it becomes hard for the water lettuce to take in as many nutrients as it needs, and thus the leaves turn yellow.

Since koi in general are prone to biting and chewing through most types of plants and roots, goldfish are a better, less adventurous option and are equally aesthetically pleasing. Otherwise, you may have to section off the part of the pond that contains water lettuce and not let the koi near it.

  • Lack of moisture can be one of the causes for yellowing water lettuce. That might sound impossible, since water lettuce, as the name suggests, grows on the surface of water, so the concept of it lacking moisture may seem silly. However, if the climate around is arid and dry, it will become difficult for the water lettuce to retain moisture, and thus the leaves can turn yellow. In such cases, growing water lettuce outdoors may not be the best option. An aquarium or an indoor garden may be a better idea, but the growth of the water lettuce will have to be more controlled.
  • In a similar vein, when water lettuce starts to turn yellow and begins curling at the ends of the leaves, it is a sign of lack of water vapor, i.e. humidity, basically. In an outdoors garden, consider using a humidifier placed close to the location of the water lettuce. Indoors, this issue is less likely to occur. Just be sure not to place the humidifier too close to the lettuce or directly amongst it, as it could weigh the plant down as well as clog up the equipment.
  • The soil type could be wrong, and the missing nutrients could be turning the water lettuce yellow. The type of soil used to grow water lettuce is not a drastic game-changer for its growth, but it is important all the same. While bottom soil is not a necessity, the right kind of soil can provide the water lettuce with adequate nutrition and keep the leaves from turning yellow. Changing the soil mix to sand and moist loam will help fix yellow water lettuce and restore its color, and will also aid in keeping the plant healthy.
  • While water lettuce has a waxy coating on its leaves that can repel excess water, many backyard ponds have waterfalls and fountains pouring on them, which, with the constant splashing, can yellow the water lettuce leaves and cause rotting. Water lettuce should be kept away from direct sources of swift water movement, and if necessary, be shielded from these sources by placing it in netted baskets.

Care tips for water lettuce

Water lettuce is a generally easy plant to take care of, but there are several things to keep in mind before planting water lettuce and while caring for it.

  • It is important to be aware that water lettuce is illegal to grow in some countries and regions. Be sure to check online for regulations pertaining to these before you bring home saplings. Another thing to keep in mind before buying water lettuce is that one should never go for the large, fully grown plants. Those are the mother plants and in a few months, being the fast grower it is, young water lettuce will quickly attain that size as well.
  • Sapling water lettuce should never be put out directly under the exposure of the sun or in moving water. Always keep the saplings in containers when you bring them, and introduce them to the pond only when they have grown and adjusted a bit. Otherwise, the roots may not be strong enough and the plant could get swept away.
  • In ideal weather and growth conditions, water lettuce thrives to the point that it can multiply swiftly and cover the entire surface of your lake or water garden. Be careful and remember to trim or uproot extra water lettuce whenever necessary, since they grow very fast and can overrun and choke the entire pond within days. Keep an eye on the water lettuce growth and separate it from other plants in the pond or garden to keep them safe. It’s a good idea to trim when you feel like the height and density is too much, and to uproot them to avoid the repercussions of swift reproduction by the plant.
  • When disposing of excess water lettuce you uprooted or cut out from the pond, never throw it in natural bodies of water, as these parts will then grow and multiply there, and can choke the entire surface soon. Dispose of the parts separately and in your waste bin, or even better, use them for composting.
  • In an indoor aquarium or water garden, you will probably be changing the water from time to time. Certain types of water may not work so well for the water lettuce and other aquatic plants, so if you are changing the water type from, say, tap water, to soft water, take the water lettuce out and keep it in containers of the new water for a day or two, and then introduce them back to the garden. Changing the water suddenly will shock the plant as well as any other living beings in the ecosystem and can cause harm overall.
  • Water lettuce does very well even when grown crowded together, but drifting is not conducive for these plants. To keep them from drifting but still letting them float a bit, you can grow them in a cluster of rocks, or create a circular enclosure using a basket, hoop or fishing line.
  • It is important to remember that water lettuce is NOT edible, unlike actual common lettuce and watercress. Water lettuce deceptively looks a lot like the open leaves of cabbage, but must not be consumed in any way. If ingested by humans, it can cause painful burning sensations in the throat, mouth and tongue and can lead to inflammation, vomiting and diarrhea. Both humans and animals should stay away from eating water lettuce.
  • When growing water lettuce, one must remember to watch out for mosquito infestation. Water lettuce offers excellent breeding space for mosquitoes, and the pond can quickly become infested by larvae and adult mosquitoes if you are not careful.

Related Questions

What other plants are suitable to grow alongside water lettuce?

Certain floating aquatic plants are good complements to the water lettuce. You can safely grow duckweed, water horn fern, Indian fern, water moss and watercress. These plants are relatively low maintenance and are less threatened by growth of water lettuce alongside.

What are the different kinds of water lettuce?

Ruffled water lettuce and Jurassic water lettuce are the common kinds of water lettuce. Jurassic water lettuce has large, flared leaves and is best for large ponds, while the ruffled variety has leaves that are wavy but never grow too big, and is hence suited for small gardens and containers.

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