Reblooming cup plant
I have a cup plant ( Silphium perfoliatum) and I would like to extend its bloom time. Would it benefit from deadheading? I know this will extend blooming in some perennials but I can’t find any info on the cup plant. The plant is thriving and covered in blooms and I want to give the pollinators more time. Thank you.
Cup plant (Silphium perfoliatum) is an excellent choice for pollinators. Unfortunately, like you, we could not find information on deadheading this particular species -- possibly because it is a wildflower and not very common as a landscape plant. Typically the bloom time of cup plants can extend from July to September or October. I would recommend trying some experiments. Deadhead a portion of your flowers and leave the rest for comparison. See if you get a second flush of flowers before the cold weather sets in. Another experiment, next year, would be to cut back a portion of your plants in late May and leave the rest unpruned. With this approach, you will get your normal flowering on some and likely delay the first flowers on the ones that were cut back. We would be interested to hear about your results!