Concerning the "dwarf" sagittaria, Sagittaria subulata. The common name "Dwarf" may be somewhat misleading. The plant will normally attain 10-15cm (4-6 inches) in height; planted very close together, the leaves will be much taller, up to 60cm (24 inches) according to Kasselmann (2003) and others, some of whom also mention age and light as factors affecting the plant's height. I had this plant easily attaining 12-15 inches when thickly planted under moderate light. I would not trim such plants. If you do want a very similar but much smaller plant, the chain sword plants like Helanthium tenellum will work. The growth habits of both can be influenced by conditions in the aquarium such as light, nutrients, and in the case of Sagittaria in particular the density of the planting. In my aquarium containing both species, they appeared identical with the only difference being the greater height of S. subulata.
Stem plants like the Ludwigia will grow relatively rapidly toward the light. This often results in good colourful growth at the growing tips closest to the light, but the lower leaves may yellow and die off, depending upon the light intensity at that level. They can then be uprooted, cut off, and the growing tips planted. Let the growth rate decide how often.
