What kills ferns? I have several types and they enjoy RoundUp. Does not even cause the ferns to wilt. These ferns have taken over about 300 square feet of my back yard. Shaded with large trees, on a down slop so they get plenty of moisture. And extremely invasive. Other than digging up the large, hard bases, there must be some chemical that works. Thanks.
Montgomery County Maryland ferns
We need to know what variety of fern you have.
Most ferns are native. Some are rampant growers. (The term invasive is usually reserved for non-native plants.) Usually glyphosate will kill or at least slow down ferns, but they have a big root system and therefore can often bounce back. You could try applying glyphosate twice with an interval of about 3 weeks. Apply in early fall, even late August. This is usually effective on the most hard-to-kill weeds.
Please keep in mind that ferns have two big pluses: deer don't eat them, and they provide good erosion control on slopes. If you plan to eliminate these ferns, another plant that's deer-proof must be able to quickly fill in the area. Otherwise, truly non-native invasive plants will ultimately move in. (And, please don't plant English ivy--it's extremely invasive!)
However, as mentioned above, it would be helpful for us to know what kind of fern you are dealing with. We may be able to provide more targeted tips. Please send us a digital photo attached to a reply.