By Penny Pawl, U. C. Master Gardener of Napa County

I can feel spring in the air, so it is time to think about which unique, beautiful plants I can add to my garden. As I peruse all the new garden and seed catalogs, I need to remember not to choose any invasive plants.

Many plants in American gardens and natural landscapes have come from another country. Over time, they have really made themselves at home. If you plant them, some of these imports will take over and crowd out native plants.

In Napa Valley, volunteers have had to remove Spanish broom from a local park. Spanish broom has bright yellow flowers and can take over a landscape in a few years.  

Many plants become invasive because nothing keeps them in check. The wild mustard in Napa Valley is a good example. It is beautiful but an opportunist, and here it has found perfect growing conditions.

My neighbor planted a beautiful grass with small seedpods. In a short time, the grass was coming up all over their yard. Then it moved to mine. It was easy to pull, but when a seed went up their dog's nose, they pulled the grass out.

A fellow Napa County Master Gardener had a beautiful wisteria. I love this plant and admired hers which was growing on both sides of her 100-year-old house. The vine had grown under one side of the house and come up on the other. No wonder it is on the invasive-plant list.

When my husband and I were new home owners, he planted a weeping willow. He sited it many feet from our well and our home, but its roots advanced quickly toward us. It had to go.

Another neighbor had a beautiful stand of giant bamboo in front of the home. It even bloomed one year and looked wonderful. But then it spread under the house's foundation. Bamboo has a life of it' own and is extremely invasive. In Hawaii, it is everywhere but it is not a native.

One of the most invasive plants is the wild oat (Avena fatua L.). I hand weeded an area of my yard overrun by this plant. It took time but I vanquished it. The following year it did not return, but in two years, there it was again.

I also fell in love with Santa Barbara daisy (Erigeron karvinskianus), also known as fleabane. It comes from Mexico and down the coast of South America. I planted a few small plants that very quickly took over the beds. It had to go. There are natives in the same family that are not such thugs.

The California Invasive Plant Council maintains a list of the most invasive plants in California (http://www.cal-ipc.org/ ). Although nurseries still sell them, these plants threaten natives by competing for water and nutrients. These plants include big periwinkle, English ivy, giant reed, iceplant, onion grass, pampas grass, red sesbania, Russian olive and tree of heaven. Scotch broom and French broom have pretty flowers but they cause changes in the soil and shade out natives. And they produce many seeds that birds move around.

Most of these plants were imported in the 1800s for landscape gardens. The plants decided they liked it here and have moved to many areas where they are not wanted.

If you don't know what to plant, pick a California native. Natives have evolved to thrive in our soil and climate without producing rampant growth. Because they are adapted to California, most do not need much water to survive.