Just like other plants, aquatic plants need to be fertilized for them to be able to thrive in your water garden. And just like regular plants, there are several different ways you can fertilize the plants and products that you can use. The point is not the actual fertilizer that you use, but that you actually use fertilizer to feed the plants.
Enhanced for Performance
It used to be that people would simply mix compost and manure with the soil in order to give it the nutrients it would need. It didn't matter if you were planting aquatic, or non-aquatic plants. The process was much the same. Today, there are several different brands of specialized fertilizer made for aquatic plants. This fertilizer is made to greatly enhance the plants' health and performance.
Correct Light and pH Levels
Before you can add any type of fertilizer you will need to make sure that you have the correct light and pH levels for the plant to properly assimilate the nutrients. If the water does not have the correct combination of pH, and light, the fertilizer is not going to do any good. It will not be used. Check the water for pH levels between 6.5 and 7 for optimal nutrient digestion and that the plants get enough light for photosynthesis.
Rate of Application
The rate at which you apply your fertilizer is going to depend greatly on the type of soil, plant size, pot size and water temperature. When the water temperature is below 70 degrees you will want to apply fertilizer at least every 4 weeks. The colder water temps will slow the rate of growth and the plants need to take in more food. Moderately warm temperatures of 70 to 80 degrees will require a more rapid rate of every three weeks. Warm, tropical water gardens of over 80 degrees should be fertilized once every 2 weeks.
Liquid or Table Substrate Fertilizers
Fertilizers are available as a liquid form that you can place directly on the plant, as a substrate fertilizer that can be mixed in the soil or used in tablet form. These fertilizers contain all of the macro nutrients that the plants needs. A liquid-type fertilizer will need to be added to the plant on a frequent basis. You need to lift the potted plant out of the water and spray down the plant according to directions. Tablet, or substrate fertilizer, will last for a longer period of time. Both are sound fertilizer options and will help the gardener keep a healthy aquatic plant.
Apply When Plants Need It
While there are certain guidelines for fertilizing plants, there will be times of the year when they need an extra boost because of the weather, water and pot conditions. Besides at the beginning of the season, or when plants are repotted after being divided, you should also look for signs of distress.
It is during these times that the plant is telling you that it needs a little more food in order to become healthy again. Once the flowers begin to blossom, when it has been unusually hot or if it has been wet for a long time with little sun, the plant will show signs of being distressed. Add some slow time-release fertilizer to the substrate, near the root system.