Aquatic plants are robust and resilient. However, they do need seasonal care. Spring is the time for thinning any plants that have grown too thick. If your plants have infringed on one another, spring is also the time to space them out again. In the summer and fall, fertilize as necessary and remove dead foliage as it appears. You can replant them quickly in the spring. If you experience cold winters, fully submerge your hardy plants, and discard your floaters. Tropical aquatic plants can spend the winter indoors.