Sites above the water level are much more endangered by invading weeds than the floating zones. Ruderals, such as Ranunculus sceleratus, Alopecurus aequalis, Epilobium spp., Bidens spp. and Juncus spp., are the most common weeds in the wetland zone of newly established plantings, and should be removed before fruiting. This is possible with weed control about four to six times a year during the first two years (establishment maintenance) until the planted species have reached a high percentage ground-cover. In oligotrophic wetland zones, the above mentioned weeds will develop slowly and only to a small size, so that weed control two or three times a year will be enough. More dangerous than short-lived weeds are competitors, especially Calamagrostis spp. and other invasive grasses. They have to be removed together with their rhizomes. If discovered too late, only a treatment with the herbicide Glyphosate will be successful. It must be painted directly on to the weed leaves but must not be allowed to come into contact with the desired plants.
This intensive weed-control maintenance is only practical on small plantings. On large urban plantings, development should be directed by mowing in early spring or late autumn, and removing the cuttings. Tall forb communities do not have to be mown each year, but a regular cycle creates tidy looking plantings. The cut material should be removed so that the sites become impoverished in nutrients. There should also be an occasional control of invasive competitor weeds. Bog and fen vegetation is best mown in autumn (October to November) to remove as many nutrients as possible.
Newly established carrs should be mown in spring each year or each second year until the tree canopies begin to shade the soil lightly. Later, only one or two cuts are enough to remove overaggressive forbs and grasses. Trees can be coppiced every 15 to 25 years to prevent them from becoming senile and to protect them from wind damage. Weeds of zones 4 and 5 are algae, and, in smaller ponds, some invasive submerged plants, in particular Elodea canadensis. This rampantly growing plant should be substituted by
Ceratophyllum species. Water-plant specialists recommend smothering Elodea populations by covering them up with large amounts of Ceratophyllum (Wachter 1996).
