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.
Canadian Thistle Patch
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.
Runoff From Neighboring Farm
Salt Residue
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 on the right 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.
Contaminated by Soil Amendment
From Pig Slaughter House
Salt and Liquid Smoke Residue