Many on Long Island whose gardens were flooded by superstorm Sandy are wondering whether it’s safe to eat vegetables grown in soil contaminated by water that not only contained salt but might have transported chemicals, bacteria and other pathogens to their gardens. Others fear plants may not grow there at all.
Both concerns are valid, but the situation is not hopeless: In the months since the storm, any contaminants carried into the soil should have been diluted by rain and dissipated by sunlight and oxygen. If vegetation appears healthy, and soil doesn’t have an off odor and isn’t discolored, shiny or abnormal in any other way, it likely isn’t contaminated by chemicals.
Sodium, however, is invisible and absolutely must be leeched out with thorough, repeated watering. Gypsum will facilitate the movement of salts through soil, as it will bind to them and carry them out, but only if used in conjunction with deep watering. The Cornell Cooperative Extension recommends applying 46-138 pounds of gypsum per 1,000 square feet and then irrigating with about one inch of water every other day for 20 days. (To gauge how much water you’re applying, put a clean, empty tuna fish can out in the garden and run a sprinkler until an inch of water accumulates in the can.) Afterward, avoid using fertilizers that contain sodium (read labels) or manure. Compost is fine, and can help give plants a much-needed nutrient boost.
If you’re concerned about damage to evergreens, flush out salts as described above, and inspect trees and shrubs, evaluating for leafless and budless branches. If you suspect they are dead, cut a piece off and check if there’s fresh, green tissue within. If branch interiors are dry and brown, they are dead and should be selectively removed.
Deciduous trees, those that lose their leaves in autumn, typically display delayed symptoms of distress. Signs to look for: yellowing leaves, falling leaves, failure to leaf out, small leaf size, no leaves at the top of the tree and insect infestation (insects are opportunistic and tend to move in when a plant is injured or weak).