After dunes are replanted the plants can be fertilized (overfertilized sea oats may develop fungus, however) -- and care should be taken that non- sand trapping plants such as St. Augustine grass do not encroach into the dune areas. (The DNR cautions against planting anything other than sand- trapping grasses and vines seaward of the control line. Lawn grasses do not help preserve dunes.) The dunes should also be mulched and watered, [Ralph Clark] said. The best mulch for dune restoration is the seaweed that often clutters up the beaches. Seaweed spread through dunes would provide vital nutrients - - potassium, nitrogen and phosphorus, Clark said.