Robert K. Watrous

landscape architecture

Milford, New Jersey


Invasive Alien Plants

I use the plants that will thrive in the region and at a particular site. Plantings often have to be appropriate for their aesthetics, deer resistance, and the microclimate at the planting site. We all should also be screening our selection of plants to do no harm. I prefer to use native plants but am not a purist. I try to moderate between the needs of the client and the needs of nature. There are invasive exotic plants I will not plant.

Some invasive plants such as the running bamboos spread aggressively by underground runners. Others such as Forsythia spread by branch rooting. These plants while aggressive are not as dangerous to the environment as those spread by seed because animals can spread the seed well beyond the confines of the garden, allowing the spread to establish in areas miles from the source plant. Once out of Pandora’s box these plants are nearly impossible to put back in. They then compete with the native landscapes often overwhelming the native plants and thus destroying the habitat for the animals that depended on the native plants.

Good sources online for invasive exotics AND native plants are:

  • The Bowman's Hill Wildflower Preserve at

  • The USDA site for Invasive and Noxious Weeds
    Unfortunately you'll notice there is no listing for New Jersey invasive plants. That's because New Jersey is one of only four States that has yet to come up with an official list of invasive or noxious plants. They have been working on it for years. Perhaps it will happen soon.

  • The Center for Invasive Species and Ecosystem Health lists US eastern region plants

  • The US Arboretum website for Invasive Plants

  • The USDA site for Plants lists invasive species
    A shortcoming of this list is the focus on only plants that are problematic to farming. This means plants like Barberry that are a problem to wild areas but not farm fields which are regularly dug up are ignored. This is slowly changing.

The following list is copied from an article in the Native Plant Society of New Jersey entitled "Invasive Plant Species" by Hubert Ling. Plants highlighted in blue are commonly available at nurseries or already exist in many gardens and often are distributed by gardeners. Most of the plants in this list are ones I will not use:

Category 1, Strongly Invasive and Widespread

Herbaceous Dicots:

  • Achillea millefolium, Yarrow
  • Alliaria petiolata, Garlic Mustard
  • Artemisia vulgaris, Mugwort
  • Cichorium intybus, Chickory
  • Coronilla varia, Crown Vetch
  • Daucus carota, Wild Carrot
  • Glechoma hederacea, Gill-Over-The -Ground
  • Hesperis matronalis, Dane's Rocket
  • Lythrum salicaria, Purple Loosestrife
  • Malva moschata, Musk Mallow
  • Meliotus alba, White Sweet Clover
  • Plantago lanceolata, English Plantain
  • Polygonium cuspidatam, Japanese Knotweed
  • Rumex crispus, Curly Dock
  • Trifolium pratense, Red Clover
  • T. repens, White Clover


  • Allium vineale, Field Garlic
  • Arundinaria, Bambusa, Any Hardy Bamboo

    While Bamboo can spread aggressively by runners it is often containable and is rarely spread by seed

  • Dendrocalamus, Bamboo
  • Cynodon dactylon, Bermuda Grass
  • Dactylis glomerata, Orchard Grass
  • Digitaria sanguinalis, Crab Grass
  • Echinochloa crusgalli, Barnyard Grass
  • Euonymus alatus, Winged Euonymus
  • Euonymus alatus compacta, Compact Winged Euonymus
  • Hemercallus fulva, Day Lily
  • Microstegium vimineum, Japanese Stilt Grass
  • Miscanthus grass
  • Phragmites australis, Common Reed

Vines and Woody Plants

  • Acer platanoides, Norway Maple
  • Alianthus altissima, Tree of Heaven
  • Berberis thunbergii, Japanese Barberry
  • Celastrus orbiculatus, Asian Bittersweet
  • Elaeaghus angustifolia, Russian Olive
  • E. umbellata, Autumn Olive
  • Hedera helix, English Ivy
  • Lingustrum vulgare , common privet
  • Lonicera japonic, Japanese Honeysuckle
  • Rhamnus cartharticus, Buckthorn
  • R. frangula, Alder Buckthorn
  • Rosa multiflora, Multiflora Rose

Category 2, Invasive But Not As Widespread (Yet)

Herbaceous Dicots:

  • Ajuga reptans, Common Bugleweed
  • Centaurea maculosa, Spotted Knapweed
  • Chelidonium majus, Celandine
  • Chrysanthemum leucanthemum, Ox-Eye Daisy
  • Dianthus armeria, Depford Pink
  • Galinsoga ciliata, Galinsoga
  • Lamium purpureum, Purple Dead Nettle
  • Linaria vulgaris, Butter-and-Eggs
  • Lysimachia nummularia, Moneywort
  • Matricaria matricariodes, Pineapple Weed
  • Mentha spicata, Spearment
  • Polygonum persicaria, Lady's-Thumb
  • Portulaca oleracea, Purslane
  • Ranunculus acris, Common Buttercup
  • R. bulbosus, Bulbous Buttercup
  • R. ficaria, Lesser Celandine
  • R. repens, Creeping Buttercup
  • Rumex acetosella, Sheep's Sorrel
  • Rumex obtusifolius, Broad Dock
  • Verbascum thapsus, Common Mullein
  • V. blattaria, Moth Mullein


  • Commelina communis, Day Flower

Vines and Woody Plants:

  • Albizia julibrissin, Mimosa
  • Prunus avium, Crab Cherry
  • Wisteria frutescens, Wisteria
  • W. floribunda, Wisteria