It’s our instinct to plant beautiful host plants next to our house. In reality, it is best to plant them 20′ and more away from the foundation. If your house is on a slope, plant host plants uphill, not downhill.
Too often people end up with an insect that is causing problems, such as termites, roaches, or ants. When the house and/or foundation is treated, the insecticide can travel laterally though the soil 15′ and more. The insecticide will then be absorbed by the host plant’s roots and the plant will become deadly to our caterpillars.
If we plant downhill, a good rain or irrigation will wash the insecticide down the slope to the roots of host plants, causing them to become deadly to caterpillars.
When we had termites in our walls, we caught it in time. Our foundation now must be treated every year but our house did not need to be tented. Each time, ant beds within 15′ of the house are soon covered with a thick layer of dead ants. Two months after treatment, I mistakenly used cudweed growing next to the house to feed American Lady caterpillars. Every one died.
Because we live in north Florida with sandy soil, we are able to have our house treated in late fall, after butterflies quit laying eggs. By spring, when butterflies begin laying eggs again, the insecticide is washed away. In the north or where soil has a good deal of clay or loam, this may not be an option. We no longer plant host plants near our house, even though we changed treatment time to late fall. It just isn’t safe enough for butterflies.