Preparing Ponds and Aquatic Plants for Cold Winter Season
Q ... I am in the planning stage of getting my pond ready for the colder months, it is heated, so I am not overly concerned about my fish. However I have a lot of marginal plants around the edge of my pond and also have watercress and mimulus in my vegetable filter. Is there any way to protect them from harsh winter weather conditions such as frost?
Nick Smith, Brighton
A ... Most plants closely associated with the water die back in the winter for their own protection. A few trees and shrubs manage to stay fairly waterlogged and not suffer, like willows and dogwoods, but they do drop their leaves and stop moving moisture and air around the plant. In the same way, the perennial marginal plants and deep-water plants die back to their roots or tuberous root stores. These will remain in suspended animation until the first glimmers of spring. This applies to your watercress (Rorippa nasturtium-aquaticum or Nasturtium officianale) but it might struggle on with your mimulus right until the frost actually bites it back. This will be no problem to the watercress, it will be one of the first plants to get going again next season, following closely behind the marsh marigold which will already be organising itself for next spring. The mimulus, on the other hand, is a hardy annual, preferring not to risk even a root or tuber to the vagaries of the climate, but hopefully by the first frosts it will have set some seed in its basket or along the pool margins that will ensure its renaissance next year.
So that means the vegetable filter will have to hold it breath. Since the everything else in the world of the pond is going to be virtually on stop and certainly very, very slow, then there should not be too much to worry about.
The best thing you can do for them and the water garden in general is to cut back the rotting dead growth as you might with most of the marginal plants. Some gardeners, particularly with wildlife in mind prefer to leave the taller or grassy type plants standing to help with animal cover and providing a food source with the seed heads. Those seeds can be a mixed blessing though in some situations and from some plants. I like grassy plants for the movement they display in the wind and some of the more tame varieties like Carex Bowles Golden or Acorus gramineus Variegatus will provide colour all the year.