New Hampshire's most common invasive species

New Hampshire regulates invasive plants under state rule Agr 3800 — 35 species that are illegal to sell, transport, or propagate anywhere in the state. Most property owners have never seen the list, but a handful of species on it show up on a meaningful share of the overgrown parcels we walk: Japanese barberry, oriental bittersweet, buckthorn, autumn olive, multiflora rose, honeysuckle, burning bush, and Japanese knotweed. Every one of them is a specific plant with a specific consequence — not just "invasives," a category too vague to act on.

Why it's not just a cosmetic problem

Japanese barberry is the clearest example. Beyond crowding out native understory, dense barberry thickets hold significantly more blacklegged ticks than open ground — field research pairing barberry stands against cleared ground has found sharply higher tick counts, and higher infection rates, where barberry goes unmanaged. New Hampshire already has one of the highest Lyme disease rates in the country. A barberry thicket at the edge of a yard is a specific, checkable reason why — not a general "ticks live in brush" claim.

Oriental bittersweet is a woody vine that climbs and girdles — it thickens around a trunk or branch and slowly chokes off the tree's nutrient flow. On a property with mature trees worth keeping, an untreated bittersweet vine is an active, ongoing loss, not a static one.

Buckthorn, autumn olive, multiflora rose, and honeysuckle share a different problem: they leaf out earlier and hold leaves later than native trees and shrubs, shading out the native seedlings and spring wildflowers underneath before they get a chance. Left alone, a stand doesn't just stay the same — it prevents the forest under it from regenerating.

What mulching does — and where it isn't the whole answer

Mechanical mulching is a legitimate, effective first strike on nearly all of the species above. Cutting them back to grade knocks the stand down hard and lets light back in for native regrowth. The honest part, which most estimates skip: almost every one of these species tries to resprout from the stump, so a single pass is a strong start, not a guaranteed finish. A property with a serious infestation is usually a mulching pass this season and a shorter follow-up check next season — not a one-and-done job, and we'll say so on the site visit rather than after.

One species is a genuine exception: Japanese knotweed spreads from cut fragments of root and stem, so mowing or mulching straight through an active stand can spread it rather than control it. If we find knotweed on a walk, that gets flagged and scoped as its own conversation — not folded into a standard mulching pass.

Why we know the list

ELS mulches vegetation and stems up to six inches in diameter — that's the scope, stated the same way on every job. Knowing exactly what's growing inside that scope, on sight, is what turns a mulching job from "clear the brush" into an accurate read on the property: what's coming out, what's staying, and what it'll actually take to keep it that way.