After a week or so of this preliminary drying move them to a warm, dry, dark area to finish curing. Curing takes about a month to complete. To finish the preservation process, coat the gourds with white shellac or polish them with a liquid wax. We know that black walnut trees produce a toxin that affects the growth of some other plants. Other ornamental plants also produce growth-reducing toxins.
Allelopathic influence goes deeper than simple competition for water and nutrients.
Actual chemical toxins secreted by one plant damage the structure and interfere with the growth of sensitive plants. If those sensitive plants are under stress or planted in heavy soils, as nearly all plants are in Montana, then the allelopathic effects will be more severe. Now, horticulture is a mixture of science and art. It is not pseudoscience, nor does it deal in the paranormal. The programs of the Montana State University Extension Service available to all people regardless of race, creed, color, sex, handicap or national origin.