The flora at Lake Hornborga is extremely varied. This is due to the fact that the conditions for vegetation are so different that many species can benefit:
- from dry meadows to deep water
- from poor mossy areas to soil rich in lime
- from uncultivated soil to grazing land and meadows
West of the lake, there are large mossy areas where the flora is limited. It is far richer on the eastern side, where the landscape is coloured white by flowering cherry trees in the spring.
Grazing cows keep the vegetation short and prevent the shores becoming overgrown with bushes and trees. Where the land consists of lime-rich fields, primarily in the north and north west, there are a number of wild orchids (such as the early marsh orchid and epipactis palustris), but otherwise the flora in the water meadows is normal. Access to the water meadows - and the whole of the lake area - is largely prohibited between 20 March and 15 July.
In the shallow water, it is possible to find wild plants such as water polygonum, nodding bur marigold, water violet, bulrushes, water dock and water hemlock. Yellow flags change the colour of some of the shores of the lake during the early summer. Many of these species produce a large number of seeds which give the ducks plenty of food.
Most of the plants here are under the surface of the water. In addition to providing food for some birds, they are also the homes of a large number of insects, which then become food for the birds. The stoneworts (Characeae) are important, as they supply the water with life-giving oxygen. Lake Hornborga is the lake in Sweden with the largest number of species of stoneworts - nine in all! The whorled leaf water milfoil and different species of pondweed are common and, together with the stoneworts, they form "meadows" under the surface of the water.Above the surface of the water, the most prominent plants are rushes and reeds. Sea club rush, blue reeds (scirpus lacustris) and twig rushes are less common.