Dahlias prefer soil that is not contaminated.
|In most cases, soil contamination is a concern when breaking ground for a new garden. If the proposed garden plot has a healthy stand of weeds, it is probably safe to proceed without a soil test. While some types of industrial pollution could be present, it is not a concern as long as ornamentals and not food plants are to be grown.
|If the proposed plot is bare or very sparsely populated with weeds or brush and prior knowledge does not provide a reason for the lack of fertility, a soil test is advised. Possible contamination types include: runoff from neighboring sites, industrial pollution, prior vegetative killer, prior over fertilization.
|If an established garden loses its fertility, contamination from over fertilization, misuse of pesticides, or excessive or contaminated soil amendments should be suspected. Unless the cause is known, a soil test is in order. The garden pictured below flourished until 1997 when supposedly good compost was added from a nearby pig slaughter house. The contamination was so high that the salt was visible on the surface and the liquid smoke aroma, though feint, was clearly recognizable.
What can be done about soil contamination?
- If a soil test indicates industrial pollution, call the EPA.
- If it is determined that runoff from a neighboring site is the cause, hire a lawyer. Otherwise you are on your own.
- If the soil test indicates the contaminate is water soluble, repeated flooding of the site may help — particularly if the contaminate is salt residue from fertilizers. If a second soil test indicates improvement, adding large amounts of composted humus will probably restore fertility quite rapidly.
- If the contaminate is not water soluble, a soil expert should be consulted.
- The final solution is to effectively replace the soil — build very high (at least 12″ of soil) raised beds with a plastic sheet barrier at the bottom. The barrier may not always be necessary, but moisture and its contaminates move from wet to dry through capillary action possibly contaminating the new soil.