In my book, this is a weed, just because it is appearing everywhere in my garden, and grows rapidly to over 4 ft. To fight it better, I would like to find out its species. Can you help me?
Zone 7.
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Sign up to join this communityIt's an Erigeron of some type, possibly Daisy Fleabane (Erigeron annuus). As you can guess from the species name, that plant's an annual - and it seeds heavily like many other annuals. It's a common weed in the upper Midwest.
There are many other species - they can be annual, biennial or perennial. There's an extensive list on this site: https://en.wikipedia.org/wiki/Erigeron. Another way to figure out which species it may be is to look at wildflower lists specific to your area of the country, then research each erigeron species listed.
If you want to control it, it's probably easiest to just hand-pull it (they don't spread by root that I know of). Using a shovel or fork can help, of course, but you shouldn't need to dig very deeply. This is best done after a rain unless you have heavy clay. If you want to enjoy the flowers first, do not let them go to seed! and then pull them. Be aware that the plant sets seed while still in bloom.
This plant is easy to kill, so no need for herbicides.
If the flowers have seedheads, I would not compost them unless your compost heap gets very hot. They'll be sure to sprout next year, otherwise.