The best time to get rid of unwanted plants is while the left side of the moon is lit. At this time most plants are concentrating on their flowers and seeds, weeds that normally won't budge when pulled, come out easily. Seed heads allow to mature now will surely drop their seed during the next moon phase. It is also the time to prune to discourage growth. How can I use this to my advantage?
Well let's look at the lowly comfrey plant. It is a perennial who self sows readily, although valueable in it's own right can quickly overtake a garden space. You are best to catch the little seedlings before they develop much of a root. Once established they are very hard to get rid of. I cut my flowers off 3 times a year.
They are a wonderful plant for attracting bees to the garden. Comfrey is used as a medicinal herb. It also speeds up decomposition in the compost. I use it to mulch, or smother, weeds around other plants too.