Some plants that have been introduced into California grow a little too well. They have escaped gardens and spread into natural areas, choking out native vegetation and destroying wildlife habitat. Lots of manual labor and herbicides are used to remove these pests from the wild. Unfortunately they are continuously reintroduced by unwitting gardeners planting them in their gardens. As these plants have come from other areas of the world, they are without their normal biological controls; that is the herbivores that would normally eat them and insects, birds and small animals that would eat their seeds, lowering their germination rate. Here are a few plants that are exceptionally aggressive and should be avoided.
This fast-growing ground cover spreads rapidly and is very difficult to eradicate. Every node can grow roots and usually does so when it makes contact with soil. It blankets large areas smothering native vegetation. Try some friendlier choices instead. For an evergreen look and blue flowers, plant Carmel Mountain Lilac (Ceanothus 'Yankee Point'). For a tough no-nonsense ground cover, try Hayes iva (Iva hayesiana).
This aggressive grass makes large, dense clumps and its seeds can spread for miles. Removing it can be painful and very difficult. Its sharp, serrated leaves can easily slice open exposed flesh, and its strong roots make it almost impossible to remove without heavy machinery. A friendlier choice is Giant Rye (Elymus condensatus) or Bear Grass (Nolina bigelovii).
Another invasive grass, this one is also spreading rapidly into wild lands and choking out native vegetation. Because of its dry kindling- like form, it can increase the risk or wildfires. Some friendlier alternatives are the tidy silver bunch grass (Fetsuca idahoensis) or a large bunchgrass like deer grass (Muhlenbergia rigens).
Sometimes known as green wattle, golden wattle, or coastal wattle, these aggressive shrubs spread into waterways as well as dry land, forming dense clumps that overrun native vegetation. If a good coastal shrub or screen is what you are looking for, try Pacific Wax Myrtle (Myrica californica) or California Coffeeberry (Rhamnus californica) instead. If you want yellow flowers, try Nevin's Barberry (Mahonia nevinii).
This nasty groundcover was planted in many coastal areas for erosion control. It has since spread out of control, overrunning many very sensitive regions and killing almost every plant in its path. A few friendlier choices are the shiny green ground cover, California Wild Strawberry (Fragaria chiloensis) or a lovely silver ground cover, Watson's Saltbush (Atriplex watsonii). Both can grow in very close proximity to the ocean and can grow in beach sand.