In the Garden:
Northern California Coastal & Inland Valleys
Scotch broom is as invasive as it is beautiful. It's like a friendly dog that bites.
Friend or Foe?
One man's junk is another man's treasure, or so it seems. This phrase holds true in the garden, as well, because invasive plants would never have taken hold if somebody at some point in time didn't think they were a good idea.
Take, for example, the noble eucalyptus tree. Native to Australia, fast growing and perfectly suited to our alkaline soil and arid climate, eucalyptus were planted by the thousands in the early part of the 1900s. Their deep roots held unstable soil on hillsides, the dense canopy provided shade, and the trees are not unattractive in appearance. However, the soil under eucalyptus trees is inhospitable to any other species of plant -- nice for weed control but tough to landscape. Personally, I rather like eucalyptus trees, but the California Native Plant Society has declared war.
Stanford University removed thousands of these trees from their campus, and Angel Island State Park was a battleground during the 1990s. Millions of dollars were spent to remove the eucalyptus, which had been planted by the military when the island was owned by the federal government. Now, only 15 years later, the trees are once again established and thriving. Unfortunately, funding for large eradication programs disappeared with the end of the dot-com boom.
The problem with an import such as the eucalyptus is that they are too successful. Slow-growing native species can't compete with an aggressive foreigner and slowly are choked out of their own territory.
Pampas grass (Cortaderia jubata) is just plain scary. Native to Argentina, pampas grass was imported for its lovely, plumed flowers and fast-growing habit and was planted extensively in the 1950s and 60s. It is now out of control, and plants can easily grow to over 20 feet tall and 13 feet around. Plants from gallon containers can grow up to 8 feet in one single season.
I'm thinking that pretty soon the coast of California will be nothing but pampas grass, and any gardener who has ever tried to remove it from their property will understand just what a menace it can be. Pampas grass bites back when tampered with. The leaves have sharp sawtooth edges that cut deeply. I have used chain saws, non-selective herbicides, shovels, and I even tried to pull it out of the ground with a truck and chain, only to have it reappear with the next rainfall. Not only is it impossible to kill, it self sows freely. Many nurseries no longer carry the plant.
My favorite invasive plant is Scotch broom (Cytisus scoparius). It is impervious to wind and poor or rocky soil and needs little or no water, and the dense green foliage is covered from February through August with abundant, fragrant, sweet pea-like yellow flowers that hold well in floral arrangements. It is abundant along freeways and hillsides, growing with no care at all, just like a weed. No wonder it was imported from Europe. However, Scotch broom self sows like the devil and now entire hillsides are covered.
A few years ago, Mexican evening primrose (Onethera) was touted as being the new "wonder" ground cover. Beautiful light pink flowers held above short, running stems seemed like the answer to a landscaper's prayer. Unfortunately, it was soon evident that the plant was difficult to control and caused a skin rash similar to poison oak in some people. It's now on the "don't" list of landscape plants.
With the disappearance of state funding to control invasive plants, the burden falls on volunteer groups, such as the California Native Plant Society and San Bruno Mountain Watch (http://www.mountainwatch.org). These groups of concerned citizens form battle lines to grub out invasives while they are small, or locate private funds to eradicate established populations.
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