During the growing season, marigolds will benefit from deadheading, which will remove old plant matter and keep your plants looking their best. To deadhead marigolds, simply pinch off old flowers above a set of new leaves or make a clean cut with gardening shears. Towards the end of the season, you may want to stop deadheading marigolds and allow a few flowers to go to seed and self-sow starts for next year’s garden.