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How to Raise Red Plants or Make Red Plants “Red”?

One of the biggest misunderstandings on the Internet about how to grow the red plants is to add fertilizer frequently or give them some red lights. Actually it is totally wrong. Raising red aquatic plants involves many aspects, including lighting, nutrients, pH level and even water temperature. This blog will explain these points one by one.

In the beginning, I want to briefly introduce why red plants are red compared to green aquatic plants? Let's talk about the general plant's green color first. As you may know, the green color is shown because the plants’ leaves and stems contain a large amount of chlorophyll, which is an important part of photosynthesis. While the red plants show red color because their leaves and stems contain a large amount of anthocyanins, such as rotala variants, alternanthera reineckii, Ludwigia super red.

So here comes another question, why do red plants have anthocyanins? What is that used for? Some studies found that, under the circumstance of strong light, the plants produce more anthocyanins to protect their chloroplasts by reflecting excessive light, because their chloroplasts are very important for their photosynthesis. On the other hand, they also absorb UV rays from the light to protect their DNA, because UV rays can damage the structure of DNA.

Strong Lighting

Based on the above two points, we can summarize that in order to make red plants more red, we need to raise them under a strong light that would “stimulate” them to produce more anthocyanins to become “Redder”. So what kind of light can be called “strong light” for red plants? We need to discuss it on four aspects - color spectrum, intensity, when to light and lighting duration time.

As mentioned above, anthocyanins absorb ultraviolet light to protect DNA from being destroyed. Therefore, when there is more blue and purple light in the spectrum, more anthocyanins will be produced and the leaves will turn red. Also, since red plants can reflect away red light, not absorb it, in order for them to produce the equivalent energy as green plants, they need to absorb more green, blue or purple lights from the spectrum. So if the spectrum of the light source contains more green, blue and purple lights, it will be more conducive to the color pigmentation of red plants.

Then what is the intensity requirement of the light? As we all know, the basis of plant growth is photosynthesis, what is photosynthesis? Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms' activities. Also, according to the energy conservation law, the first law of thermodynamics, it states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed. Therefore, if you want your plant to grow well, grow fast and grow strong, the prerequisite is sufficient light energy + enough raw materials (CO2 and other nutrients) to convert into sufficient chemical energy (Plants growth), especially red plants.

Then we need to talk about when you turn on the light every day. Generally speaking, it is better to match the biological clock of the plants. Because of the influence of natural light, the leaves generally open naturally at eight or nine in the morning. If the lights are not turned on at this time, less anthocyanins but more chlorophyll would be produced inside of the red plants, so new leaves would turn greenish. Therefore, try to turn on the light following the normal biological clock of the plant. The sooner the light is turned on, the more helpful it would be on the color pigmentation.

How long does the light need to be turned on? As mentioned earlier, red plants’s chlorophyll are easily covered by their anthocyanin, which means that little chlorophyll is available for photosynthesis. So they may need long time lighting to ensure adequate photosynthesis for their growth. The specific time depends on different water quality and how powerful your light is, but generally, it should not be less than five to six hours. Some people may even need to light ten to twelve hours a day. So do some simple tests to figure out the best duration time for your plants.

Controlled Fertilization

Iron is not necessary for the formation of anthocyanins but it is required for the formation of chlorophyll, though, for the green color, therefore it is wrong to add lots of iron fertilizer into the water in hopes that the plants would turn red.


As mentioned in other articles, with a limitation of the nitrogen and phosphate level, red plants look more reddish and vibrant. So you need to keep water lean in fertilizer (especially nitrogen). How to lower the nitrogen and phosphate level? You may increase the frequency of water change in a week (like 2-3 times of 10-20% water change) to dilute various material in water, or reduce the frequency of dosing the fertilizer.

CO2 Supplement

As mentioned above, red plants look red because they contain anthocyanins. While the production of anthocyanins depends on the "sugar" material (Glucose) in the plant; plants must be rich in sugar to produce more anthocyanins. The production of sugar requires a lot of "carbon elements". The source of carbon elements in aquatic plants is mainly from the carbon dioxide in the water, so we understand again that red aquatic plants need more carbon dioxide to produce sugars and then produce anthocyanins. Therefore, CO2 is a must for raising the red plants.


Lower Temperature

The red plants prefer to grow in the water with a slightly lower temperature. Why? Just like the leaves turn brown or red in the fall. Chlorophyll likes to be formed at high temperatures, slightly lower temperatures will reduce the formation of plants’ chlorophyll and contribute to the formation of anthocyanins which would turn the plants look reddish. Additionally, The lower the temperature in the water is, the better the light penetration will be. When the water temperature is slightly lower, it is more conducive for the light energy reaching the plants for growth and color pigmentation. The ideal water temperature for red plants is between 20-23ºC (68-73.4ºF).


PH Level

The PH level is often overlooked when we talk about how to raise red aquatic plants. Anthocyanins would turn red if the PH level surrounding it is under acidic conditions while it would turn blue or purple if the PH level surrounding it is alkaline conditions. Normally, with adding enough CO2 into the water, it is easier to reach the ideal PH level between 6.0-6.8 for the red plants. You may monitor the PH level by adjusting the amount of carbon dioxide you add into your tank.

In summary, strong lighting, controlled fertilization, CO2 supplements, slightly lower temperature and acidic PH level are top priorities for growing red plants under the water. Hope those tips may help you achieve your desired plants goals. Thank you.

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