Sacrificial Planting - Marigolds
(Adelaide, SA, Australia)
A few months ago I planted an alternating border of Sage and Marigolds on two borders of a 1m by 1.5m Leafy greens Garden Bed. The intent was to have an attractive border with some culinary uses.
Within a few days the Marigolds were being eaten, not too badly at first so I decided to use the Marigolds as Sacrificial Plants.
This appeared to work well at first. The Sage, Spinach, Nasturtium and Silverbeet were all unaffected. At first.
Two weeks after initial plantings of Marigolds almost all of them on the long border were consumed to the ground, the next evening the rest of the Marigolds were consumed to the ground. The next evening all the other plants(including the Sage) were badly damaged by the pests.
I went out with a torch and bug guide the next night and found some Cutworms and an unknown winged pest plus a very large number of Slugs and Snails. I picked as many of the cutworms and Slugs/Snails as I could and disposed of them. I then spread slug bait around to finish them of.
I observed that there were no slugs and snails visible elsewhere in the Garden, were normally there would be a small number. It appears that what happened was twofold;
One - the Marigolds attracted pests from further away than would normally be an issue for the Garden Bed in question.
Two - the slugs and snails being well feed increased in size faster than normal and with that came the predictable increase in diet.
I have concluded (backed up with subsequent Google Search's) that when Sacrificial Planting is necessary, to know the pests likely to be encountered and their numbers/growth rates. Using that one can then plant the appropriate number of Sacrificial Plants. Bearing in mind it would be easy to breed up a large number of the relevant pests to the detriment of the garden.