Use only those that are free of harmful pesticides. Spilanthes oleracea is also called para cress. Another species, Spilanthes acmella, is also known as the toothache plant and it is called salad cress. I have white, fuzzy worms on my plants. There are lots of lemons on it but some of the leaves are yellow.
Citrus naturally drop leaves during the year, particularly when putting on new growth.
But sometimes too much water can cause leaves to yellow. Citrus demand good drainage, so improve that in your container if water does not flow rapidly through the soil. You'll want to keep the soil evenly moist, but not overdo it. If you're seeing wilting and yellowing leaves, your plant is getting too little moisture. Salt buildup also can cause leaves to yellow.